Time Machines: Scientific Explorations in Deep Time

T i m e Machines © 1998 Springer-Verlag New York, Inc. All rights reserved. No part of this publication may he repro...

Author: Peter D. Ward

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T i m e

Machines

© 1998 Springer-Verlag New York, Inc. All rights reserved. No part of this publication may he reproduced, stored in a retrieval system, or transmitted, in any form or hy any means, electronic, mechanical, photocopying, recording, or otherwise, without the ptior written permission of the puhlisher. Published in the United States by Copernicus, an imprint of Springer-Verlag New York, Inc. Copernicus Springer-Verlag New York, Inc. 175 Fifth Avenue New York, NY 10010 Ward, Peter Douglas, 1949Time machines / Peter Ward, p.

cm.

Includes bibliographical references and index. ISBN 0-387-98416-X (hardcover: alk. paper) 1. Paleontology. QE711.2.W37

I. Title.

1998

560—dc2I

98-18393 Ml'

Manufactured in the United States of America. Printed on acid-free paper. 9 8 7 6 5 4 3 2 1 ISBN 0-387-98416-X

SPIN 10659445

Contents Preface

vii

Introduction: Sucia Island PART

1

O N E :

F I N D I N G

TIME

J

Fossils and the Birth of the Geological Time Scale 2

Radiometric Clocks 3

PART

4 5

xi

Magnetic Clocks T W O :

33 45

PLACE

Baja British Columbia

71

73

Ancient Environments and the Level of the Sea

PART

T H R E E :

6

I N H A B I T A N T S

The Bite of a Mosasaur 7

Virtual Ammonites

127 147

8

The Ancestry of the Nautilus

9

Of Inoceramids and Isotopes

v

3

169 J 91

105 12 5

T I M E

PART

F O U R :

M A C H I N E S

THE

10

TIME

Cretaceous Park Afterword

223

References

225

Index

vi

231

M A C H I N E

207

2 0 5

Preface

In modern times, science has brought t h e p a s t — a n d so many of its creatures—back to life via intellectual inquiry, application of t h e scientific method, and some extraordinary technology t h a t has recently been developed. T h e wonder of t h e process is t h a t such a rich and vivid understanding of the deep past has b e e n generated from such scanty evidence: b r o k e n bones, lithified shells, fossil leaves, and e v e n simple layered rocks. T h e scientists w h o h a v e contributed to this work h a v e w o v e n rich tapestries of ancient times, and their weaving, w h i c h is an a d v e n t u r e in itself, is t h e subject of this book. It is as if true time m a c h i n e s existed, enabling us to retreat through time's mists into t h e past, to e x a m i n e the then-living as t h o u g h living still, to visit a n c i e n t worlds and reconstruct t h e lives their denizens led. vii

T I M E

M A C H I N E S

T h e past tantalizes us; it is part of our n a t u r e to seek clues about ancient times and our origins. Yet t h e past is far more t h a n just some m o m e n t in time. In our o w n lives, for instance, it is also place, people (and other living things), and history. Take t h e first day of school: t h e desks and posters, the windows and chalkboards, t h e people w h o left us there, the people we met. So, too, for paleontologists and archeologists is the deep past a convergence of time, place, i n h a b i t a n t s , and their history or biological interactions. To bring a dinosaur to life, you must journey back to a given time, the Mesozoic Era, t h e so-called A g e of Dinosaurs t h a t ended 65 million years ago. But o n c e there, you are in a place filled with life, and you must be able to understand t h a t a n c i e n t e n v i r o n m e n t and its a n c i e n t inhabitants. To reconstruct t h e past, it is necessary to study all of these dimensions. In paleontology we study t h e past in many ways. We use theory, computers, intricate laboratory e q u i p m e n t , and e v e n t h o u g h t experiments. Most commonly, however, to bring the past back to life, we use rocks. T h e rocks we look at are usually layered or sedimentary (as opposed, say, to lava). T h i s is t h e type of rock t h a t c o n t a i n s fossils, and it is fossils t h a t provide the key to the hoary vaults of time. S e d i m e n t a r y rocks thus c o n t a i n t h e best information we h a v e for studying t h e past—if only we c a n access t h a t information. A n y outcropping of fossil-bearing rock holds clues to its age, and thus to t h e age of t h e fossilized remains it harbors. T h e same rocks may

also

hold

clues

to their place

of origin, w h i c h m i g h t be very different from the place where they rest now. T h e surface of t h e e a r t h , after all, is n o t static but restless, its present position just a snapshot during n e v e r - e n d i n g voyages from and to. Rocks also can yield clues to t h e n a t u r e of t h e e n v i r o n m e n t s where they were formed: Did t h e materials of w h i c h they were composed " t u r n to stone," or lithify, on land, in a lake or sea, or in a desert? W a s t h e e n v i r o n m e n t warmer or colder, more saline or fresher, richer or poorer in oxygen or in carbon dioxide t h a n our e a r t h today? Most crucial of all, these same rocks usually contain our best clues to reconstructing t h e history of t h e a n c i e n t life (and d e a t h ) of living forms t h a t were present w h e n t h e rocks we are studying were taking shape. viii

P r e f a c e

No single scientific operation or approach extracts all this disparate information. Many scientific tools, techniques, a n d philosophies must be brought to bear. We might call these devices time machines. T h e y vary from a rock h a m m e r to a mass spectroscope. Many scientists spend their lives using these time m a c h i n e s to resurrect the past. T h e results c a n be spectacular, fueling t h e fascination of popular culture with dinosaurs, for example, or they can be more m u n d a n e . T h e r e are many ambiguities, however. T h e past no longer exists; it is really n o t h i n g but a m e m o r y — a memory of a loved o n e or an e a r t h long past, of personal happiness or sadness or of creatures long dead. A n d memories, as we all know, are often ephemeral. Two people w h o a t t e n d e d the same e v e n t , or lived t h r o u g h t h e same history, often h a v e q u i t e different m e m o r i e s of what transpired. Interpreting t h e fossil record can be like that. Different witnesses—or different time m a c h i n e s — o f t e n yield quite different accounts of what occurred. T h u s there are usually multiple versions to choose from reconstructing the past. Deciding which represents "the t r u t h " may be difficult. Yet ambiguity is a necessary—and n o t entirely u n w e l c o m e — a s p e c t of studying the deep past. It h a p p e n s ; people argue; t h e arguments are generally resolved, and scientific progress is usually ( t h o u g h n o t always) t h e result. Ambiguity is thus an acceptable by-product of using time m a c h i n e s to study the past, and it is o n e of t h e subjects of this book. It also greatly e n h a n c e s t h e wonder and fun of doing the types of science c o n c e r n e d with the study of t h e past. I wrote this book to show how t h e past is reconstructed by those of us w h o study geology and p a l e o n t o l o g y — h o w scientists in these fields use specific scientific techniques and instruments to resurrect a n c i e n t worlds. Part of that process involves decisions about w h i c h of many memories dredged from t h e past we should give most credence to. No single time m a c h i n e recreates an entire picture of t h e past; e a c h is like a single color or brushstroke, by itself often meaningless. Yet w h e n c o m b i n e d with others, each contributes to a c o m p r e h e n s i b l e — a n d often beautiful—portrait of t h e past. To show this process, 1 h a v e profiled a very specific "past" by looking at a particular time and place and at its i n h a b i t a n t s . Many others would do just ix

T I M E

M A C H I N E S

as well, of course. T h e destination of my time m a c h i n e was chosen simply for its familiarity a n d for t h e beauty of its time, its i n h a b i t a n t s , and its story. T h e time interval was b e t w e e n 80 and 65 million years ago, near the end of the Cretaceous Period, itself t h e last interval of t h e so-called Age of Dinosaurs. T h e place n o w exists in t h e region around Vancouver Island, most specifically a tiny island in W a s h i n g t o n state given t h e n a m e Sucia. T h e inhabitants are mostly dead: a m m o n i t e s , mosasaurs, clams, and snails; they also include t h e still-living nautilus. T h e i r story unfolds in t h e pages to follow. Finally, e v e n t h o u g h t h e picture we paint is composed of strokes of colors discovered by a variety of scientific m e t h o d s — t h e so-called time m a c h i n e s — l e t us again acknowledge t h a t t h e actual painting is always d o n e by us h u m a n s . T h e data blink u n c o m p r e h e n d i n g l y from t h e myriad machines. No life animates these results w i t h o u t a h u m a n touch. Interpretation of t h e data is the final step t h a t breathes life into t h e d e a d — t h e most fascin a t i n g part of t h e study of t h e deep past. T h e idea of a book describing h o w scientists interpret t h e past came from Jerry Lyons, my editor on two previous books. O v e r several lunches, he and I envisioned a book wherein each c h a p t e r dealt with o n e type of analytical technique or laboratory m a c h i n e that gives us a window into the past. Radiocarbon dating, functional analysis, paleoecological and other techniques— each would b e c o m e an i n d e p e n d e n t essay, for e a c h is o n e of t h e "time m a c h i n e s " from w h i c h this book derives its title. T h e wonderful o r n a t e creation of H. G. Wells's novel The Time Machine is t h e obvious source of t h a t title. Yet Wells's story was about the future. O u r a d v e n t u r e beckons us to travel in quite t h e opposite direction. Settle in, buckle your seat belt, and ease back t h e controls.

Introduction: Sucia

Island

A n y voyage of discovery into t h e past must begin at some site or dig where we find evidence of a n c i e n t times and lives. A pharaoh's t o m b , a mastodon's grave, a trilobite's s t r a t u m — a n y trip into t h e past begins in a m o d e r n reality that is usually dusty and cold. We w h o study t h e past h a v e given these places a multiplicity of names: An outcrop. A stratigraphic section. An exposure. A stratum or bed. All are n a m e s for t h e rocks themselves, t h e tombs holding so many secrets of long ago. Sites t h a t give access to t h e past are c o m m o n . All that we need are locales with well-exposed sedimentary or layered rock and, of course, a time m a c h i n e or t w o — t h e t e c h n i q u e or laboratory procedure that scientists use to discover t h e n a t u r e of an a n c i e n t time, place, i n h a b i t a n t , or

XI

T

I

M

E

M

A

C

H

I

N

E

5

history. T h e choice is thus which site to sample, which graveyard to loot, which bodies to e x h u m e — a n d which kind of time m a c h i n e to engage. I h a v e taken t h e liberty of picking o n e such graveyard as the doorway into time t h a t provides t h e structure of this book. T h i s particular portal takes us back to t h e Age of Dinosaurs, but at a locality that offers evidence of sea life, rather t h a n life on t h e land. It is positively writhing with Mesozoic-aged ghosts—from t h e time of the dinosaurs—and is as physically beautiful as any place I h a v e visited on earth: Sucia, a small island just south of British C o lumbia, where we can operate our time m a c h i n e s with unfettered a b a n d o n . All we h a v e to do is get there. T h e voyage starts c o n v e n t i o n a l l y e n o u g h . Pack the car, fill the tank, and head n o r t h out of Seattle on 1-5, past the satellite suburbs and parasitic strip malls engorging themselves on t h e city's flanks. Soon we pass through Everett, h o m e of pulp mills and aircraft carriers, and t h e n into a less populated countryside. After an hour we reach M o u n t Vernon, looking n o t h i n g like its more famous eastern namesake. N o w we leave the interstate for a highway t h a t shoots west across t h e flat, tulip-and daffodil-laden Skagit Valley, passing t h r o u g h fertile acreage. T h e dirt of these low fields finally gives way to harder outcrops. N e x t c o m e oil refineries, estuarine water and sloughs, and finally t h e literal littoral, the shore itself. We slowly pass t h r o u g h the t o w n of A n a c o r t e s , a mile of gas stations and last-chance eateries and t h e n travel four miles along a scenic coastal road to arrive at a ferry terminus, where the wide m o u t h s of great, squat, green and white Washingt o n S t a t e ferries are either engulfing or expectorating cars. T h e y are aimed n o r t h and west, toward t h e curiously n a m e d San Juan Island, a rocky promin e n c e seemingly floating on a placid inland sea. T h e ferry ride is unremarkable, but t h e scenery is spectacular whatever t h e season. T h e ferry snakes t h r o u g h t h e rocky islands, stopping here and there, heading ever n o r t h w a r d , at last arriving at Orcas Island, most populous of t h e S a n Juan group. O n c e again a road leads through bucolic countryside, twisting past farms and second- or third-growth scrub forest, with the most b r e a t h t a k i n g views given and immediately t a k e n away. Finally a thin lane turns off the country road, private this time, descending an unhurried XII

I n t r o d u c t i o n

slope until a long gravel beach of cobble and shingle beckons. But the real show is to the north, where many small islands sit silently like Dewey's fleet anchored in Manila Bay. N o w the choice of transportation becomes tricky and improvisational. It has to be a boat capable of crossing two miles of wind-whipped sea. A Zodiac works fine, but harder boats will do. Tide is a consideration, for the N o r t h Beach of Orcas Island experiences 15-foot tidal swings; sometimes you launch right off the drifted logs t h a t mark t h e highest part of t h e beach, and sometimes you must drag t h e boat across 100 feet of gravel and mud to reach the water. G e a r is stowed, a prayer and a pull and t h e m o t o r coughs, starts, belches gray noxious smoke and you point h e r n o r t h — e v e r northward this journey d i c t a t e s — t o the last bit of subaerial U n i t e d States territory bowing before the great expanse of C a n a d a . Kelp beds (and a few drifted logs) are our only c o n c e r n on t h e water. Sea birds keep us c o m p a n y as the long, low island approaches, its stone cliffs festooned with verdant arboreal b a n n e r s n o w looming large. Landing sites are no problem; the entire island is a S t a t e Park, and two splendid docks exist for t h e well-to-do yachters w h o call this place h o m e during t h e summer season. No ferry touches here, and there is no way to arrive o t h e r t h a n by private boat. T h e mooring facilities lie at the end of a large inlet appropriately called Fossil Bay. We glide in slowly, t h e flat water of this protected inner bay as green as the trees straining high overhead on either side. T h e r e is no escaping the cathedral-like presence of the stern rocks here. Vertical cliffs line the bay, tan in color on o n e side, greenish and dark on the other; these are serious rocks drenched in history—a graveyard. T h e bay seems to suck away sound and demands reverence. Dawn patrols of eagles are chased by gulls. O t h e r boaters t h r o n g this harbor in summer, but they seem e p h e m e r a l and are easily ignored, ghosts a m o n g t h e ghosts. A few park rangers t h i n k they run the place, yet even they leave with the warm weather. N o t t h a t this matters. On Sucia Island, it is even more suitable to travel back into time in winter t h a n in summer; it is far more lonely and deserted t h e n , as suits a graveyard. Mil

T I M E

M A C H I N E 5

T h e long w o o d e n planks of t h e island's piers give way to a path, and the tan rocks c a n n o w be seen to be massive sandstone, e t c h e d by the curious tracings t h a t are t h e hallmark of water m o v e m e n t — i n this case ancient water m o v e m e n t , for t h e rocks are fossilized sand dunes, incongruously frozen into rock in t h e middle of their a n c i e n t migrations. A b a n d o n e d quarries line the path, where great h u n k s of this speckled sand-dune rock were cut and carried away to b e c o m e part of so m a n y buildings erected in circa-1900 Seattle. T h e tan rocks, t h o u g h they are part of our story, are n o t the reason we h a v e made our long journey. S u c h rippled rocks left b e h i n d by a n c i e n t rivers are c o m m o n on our planet's surface, e v e n if they do date to the earliest epochs of t h e A g e of M a m m a l s , as these rocks on Sucia do. T h r o u g h scientific means t h a t are t h e subject of this book, they h a v e been shown to be a part of a n c i e n t N o r t h A m e r i c a , deposited h e r e 50 million years ago, soon after a great land mass crashed into this coastline from the southwest. This c o n t i n e n t a l collision was an a n c i e n t disaster, where an offshore island sailed in, m i l l e n n i u m by m i l l e n n i u m , like some slow ghost ship, and finally ran aground on this part of N o r t h A m e r i c a , welding itself to our c o n t i n e n t in the process. T h e t a n rocks are t h e first to h a v e formed after this a n c i e n t collision. T h e y are like a series of Band-Aids plastered over the scar marking the collision. C o n t i n u i n g our m a r c h inland, we walk across a grassy plain dotted by campgrounds. More rocky cliffs loom just ahead, these made up of the thick, dark green siltstone and shale t h a t form the o t h e r side of t h e eponymously n a m e d Fossil Bay. T h e first fossiliferous outcrops appear: blocky, rubbly, and dark. T h e y are olive-green sedimentary rocks but filled with pale, golfball- to footballsized h u n k s of limestone called concretions. H o w a fossil h u n t e r loves to see these round c o n c r e t i o n s bobbing in a sea of shale! Each formed around some e n t o m b e d nucleus t h a t , more often t h a n not, is a fossil. T h e first c o n c r e t i o n sits ripe for a whack. A test blow with a h a m m e r — t h e first of t h e m a n y blows of a long day—loosens t h e arms and tells a lithic tale; t h e silty matrix is hard, but the round concretions are harder still, small booby-trap grenades waiting to shoot rock fragments into t h e eyes of the unprepared amateur. T h e con\1V


cretions here on Sucia can be t h e hearers of wonderful treasure—they often c o n t a i n exquisitely preserved fossilized shells. T h i s place is unique in t h e state of W a s h i n g t o n : It is t h e o n e locality where anyone can immediately find a b u n d a n t , unmistakable fossil remains from the Mesozoic Era, the so-called Age of Dinosaurs. N o t dinosaurs t h e m selves, worse luck, for n o n e of these mighty icons h a v e been found on the island—yet. But o t h e r types of fossils from t h a t era are a b u n d a n t . Sucia readily yields t h e remains of long-dead creatures so different from a n y t h i n g inhabiting the oceans today t h a t they force us to confront t h e reality of extinction and the enormity of geological time. O u r prime locality, Fossil Bay, faces southeast, framing t h e e n o r m o u s peak of Mt. Baker t h a t presides over t h e t o w n of Bellingham on t h e distant mainland. T h e bay is a product of glaciers, w h i c h ran parallel to t h e bedding of these steeply tilted rocks. G r e a t boulders line its shore, boulders fallen from above, and everywhere t h e rocks are covered with a white patina of fossils, like white paint splattered by some unruly sky painter. T h e dark shale and concretions alike c o n t a i n these n u m e r o u s fossils. T h e y are white, or e v e n iridescent, and they call out like beacons. Most of the fossils c o m e from t h e shells of snails and clams of types long extinct. T h e most c o m m o n and noticeable are t h e inoceramids; they are large and concentrically ribbed. Also immediately visible are t h e knobby, triangular clam fossils called trigoniids. Both of these fossils whisper " n o t of your t i m e " as they fling back sunshine with their pearly luster. O t h e r fossils here look much like clams and snails found in our world today. But n o n e of these are the true treasures. Scattered a m o n g t h e smaller and more c o m m o n fossils are iridescent shells in the shape of arcane spirals or straight h o r n s , o r n a m e n t e d with a panoply of ribs and delicate, flower-like sutures. T h e s e are t h e ammonites, prizes of the Mesozoic conchologist. From inches to a foot across, they are nestled in their rocky sarcophagi, waiting for t h e precision blow that sets t h e m free. A few fossil nautiloids may be found as well, along with such rarer treasures as perfectly formed shark teeth. Lost shards from a lost world. Sucia Island, t h e last parcel of U n i t e d States territory jutting against the immensity of C a n a d a , is for us on this day a destination. But Sucia is also

T I M E

M A C H I N E S

but the start of a journey, b o t h geographically and temporally. It will become clear t h a t this island, these fossils, raise more questions t h a n they answer. A wider view will be needed if we are to find meaningful answers to questions about the age, e n v i r o n m e n t s , and i n h a b i t a n t s of this region's past. O t h e r sedimentary rocks must be e x a m i n e d and compared with those found on Sucia—rocks b o t h slightly younger and o l d e r — a n d for these we must travel o n c e more. To t h e n o r t h and west of Sucia lie o t h e r islands with rocks Mesozoic in origin. Like Sucia, they are packed with fossil shells, and in some cases they harbor fossil bones as well. On nearby Vancouver Island, a complete, fifty-foot skeleton of an a n c i e n t , sea-going reptile of the Plesiosaur family was recovered in the early 1990s. It was o n e of the largest and finest examples of these long-necked m a r i n e reptiles from the A g e of Dinosaurs ever recovered. A year later, t h e skull of a mosasaur, a n o t h e r type of gigantic m a r i n e reptile from t h e Mesozoic Era, was found on an adjoining island—a place called Hornby island that will l o o m large in our travels. All of these

T h e south coast ol Sucia Island.

xvi


places and their creatures will b e c o m e our intellectual territory, t h e d o m a i n we will explore with our time m a c h i n e s . A l o n g t h e shores of t h e Inland Sea b e t w e e n V a n c o u v e r and Victoria for 100 miles and more, a gigantic expanse of strata lies draped over islands and m o u n t a i n s , lining bays and rivers, ready to tell tales of t h e A g e of Dinosaurs if only the observer can u n e a r t h t h e information. T h i s suite of rocks, which includes those of Sucia and H o r n b y a n d a t h o u s a n d o t h e r localities, is all part of the N a n a i m o G r o u p , strata in aggregate almost t h r e e miles thick, named after a t o w n on Vancouver Island. T h e s e rocks merit our a t t e n t i o n for many reasons, n o t least for the pristine fossils they c o n t a i n and t h e glimpses of the past they afford. T h e N a n a i m o G r o u p shale that carpets this region is a r e m n a n t seabed of great antiquity, its muddy layers stacked o n e upon a n o t h e r in interminable fashion by the passing of ancient time, each older layer buried by new sediment that in the process covered the newly dead. Each successive sedimentary bed was compacted, flattened, and harrowed by worms and urchins, finally turning to hard rock and enclosing all of the collected shells from animals living in that long-ago place. But there are other rocks as well, rocks that originally formed in long-forgotten rivers on ancient beaches, or in lakes and swamps; the N a n a i m o G r o u p is the remains of 20 million years of earth history where the records of tumultuous changes in both the e n v i r o n m e n t and the life forms that inhabited it are inscribed. W h a t were the creatures t h a t lived in this a n c i e n t place really like? W h e r e did they live? If we could only go back to t h e time w h e n t h e gray sand and silt now frozen into stony c e m e n t were being d e p o s i t e d — w h e n t h e ceramic-like shards wrenched and p o u n d e d from t h e hard rock were n o t the relict of then but part of now. W h a t would t h a t ocean b o t t o m and those creatures look like? T h e only solution would be for s o m e o n e , s o m e h o w to build a time m a c h i n e and actually return in time to t h e Age of Dinosaurs. Impossible, of course. But there are time machines, of a sort, t h a t enable us to reconstruct a n c i e n t fossil c o m m u n i t i e s . T h e s e time m a c h i n e s c o m e from science. T h e y are t h e scientific m e t h o d itself, along with t h e many kinds of devices it has spawned: mass spectroscopes, CT scanners, magnetometers, XVll

T I M E

M A C H I N E S

D N A sequencers, microscopes of every stripe, ion beam microprobes, radioisotope geochemistry labs, P C R techniques, supercomputers and Silicon Graphics Indigos, and e v e n simple rock picks are t h e entryways into deep time. W i t h our m o d e r n m a c h i n e s t h e r e is a way to go back to a place such as a n c i e n t Sucia Island, long before it emerged from the sea to become an island of green trees and gray cliffs with t h e power to beguile a voyager willing to unleash t h e power of science to learn about t h e past.

Locations of Upper Cretaceous Nanaimo Group strata in the Vancouver island region. xviii


Many such time m a c h i n e s h a v e b e e n applied to the rocks and fossils of the Sucia Island region. Yet in t h a t regard Sucia and its environs are far from unique. T h e r e exists an immense scientific literature detailing t h e myriad studies carried out in countless localities around t h e globe, profiling a seemingly endless series of different "pasts," e a c h its o w n rich a n d complex world. T h e examples offered in this book are drawn from just o n e such place. T h e "past" of Sucia island is unique, but t h e way we h a v e c o m e to understand it is not. It is as t h o u g h the shopworn science fiction c o n c e p t of there being many parallel universes were indeed true, for t h e various time m a c h i n e s h a v e revealed countless and varied "past." T h e past, t h e n , seems to be m a d e of a series of slices like those of a CT scan, where no single study reveals t h e whole; for an entire picture to emerge, we need m a n y such slices, e a c h derived from its own type of time m a c h i n e .

O u r first day on Sucia has passed. We sit on a gravel beach at sunset looking west from our campsite, all around us water, some real, some turned to rock. In the nearby sea, t h e night creatures stir. T h e fish and invertebrates teeming in t h e productive Puget S o u n d waters are c h a n g i n g shifts, and in t h e fossil shale we can imagine a c h a n g i n g of the guard as well. A m m o n i t e s rise from cold graves; fossil nautiloids resume their scavenging; snails and clams dance o n c e more across muddy sediment. O u r campfire dances too, and nearby a stir-fry on t h e propane stove sends delicious aroma into t h e sky. Venus now outshines t h e waning sunset, and muscles t h a t ache from a day smashing fossils out of unwilling rock beg for a t t e n t i o n . W a r m darkness n o w surrounds us like a fleece. T h e last light now, t h e fire sends sparks to rival t h e S u m m e r Triangle overhead, and time slides smoothly along its two t r a c k s — o n e into t h e deep past, w h e n a m m o n i t e s swam the sea among Mesozoic saurians, a n d into t h e near past as well, w h e n we all first grew curious about t h e bestiary of t h e d e e p past. As sleep settles in, a last t h o u g h t lingers about t h e tasks to be faced on t h e c o m i n g day: the study of time itself, the first step in recreating a past.

XIX

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H o w old are t h e rocks o n Sucia Island? H o w m a n y years ago were the greenish sandstone and silts so rich in fossils not t h e stony outcrops we see today, but rather a vibrant, living seabed, h o m e to an entire bestiary of extinct organisms? H o w long ago did t h e long-necked, scaly sea reptiles and archaic shelled mollusks live their lives? H o w long ago? We c a n n o t bring back to life this world gone by until we k n o w its age. Finding t h e age of Sucia Island is our first task in this journey, just as it is usually t h e first scientific project u n d e r t a k e n as by every n e o p h y t e geologist. Geologists face t h e same central question in all of their studies: H o w old is the rock they are studying? For t h a t matter, how old is t h e earth? W h e n

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did a given m o u n t a i n c h a i n form, or an a n c i e n t sea? W h e n did a particularly interesting or i m p o r t a n t evolutionary e v e n t occur? T h e tools we need to take these first steps in reconstructing t h e past vary from t h e simplicity of a rock h a m m e r to t h e arcane electronics of an atom-separating mass spectrograph. H o w do you tell time in t h e present? You look at your watch or the clock on t h e wall. A n d if no clock was available? You listen to the radio or watch television and wait for some a n n o u n c e m e n t of t h e time. But say these avenues are cut off as well. N o w you must rely on far more basic and crude time keepers: sunrise and sunset. Perhaps you can estimate high n o o n . But the middle of the night on a cloudy evening? R e m o v e technology, and time becomes a very different—and difficult—quantity to pin down. W i t h o u t technology, time moves from t h e absolute to the relative— with no recourse to an external standard, one's ability to d e t e r m i n e time becomes a relative measure. Day follows night; midday follows morning; a grumbling s t o m a c h follows sleep. Time-keeping in such circumstances is very crude, just like trying to date a r a n d o m fossil found on a beach. You h a v e awakened in t h e middle of t h e night, wondering what time it is; you have found a fossil on t h e beach, wondering h o w old it is. W i t h o u t some c o n t e x tual information and with no technology available, you are lost. But even here t h e m e t a p h o r breaks d o w n . In t h e middle of the night you find your watch, and t h e riddle is solved. But with t h e fossil on t h e beach, there is no w a t c h t h a t will ever help you, no m a c h i n e t h a t will ever pin down this fossil's age in a n y t h i n g o t h e r t h a n great crude swaths of million-year, or even hundred-million-year intervals. No wonder the early geologists wrestled so determinedly with this problem. More t h a n any o t h e r field of science, geology is inexorably linked to t h e concepts of time. T h e science of geology has b e e n described as t h e science of telling time—establishing dates and sequences of earth events. Sooner or later any geological investigation moves from process to history, and thus to events t h a t occurred during t h e passage of some discrete time interval in t h e past. To a geologist, measuring time is almost a religion. In no other field of science has it been necessary to codify a time scale applicable only 4

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to, and usually k n o w n only to, specialists in t h a t field. T h e r e is no formalized biological time scale or chemical time scale, e v e n t h o u g h all processes described in these two great disciplines h a v e temporal c o m p o n e n t s . All other fields of study simply use t h e familiar intervals of time: seconds, minutes, hours, days, and so on. Geologists, on t h e o t h e r h a n d , talk about periods and epochs, eras and zones, stages and series—the vast subdivisions of w h a t is k n o w n as the geological time scale. Time is clearly indispensable to and intertwined with the study of geology. Perhaps this is why geologists seem a bit obsessed by time and its m e a s u r e m e n t and h a v e b e e n so since t h e birth of their science. Efforts to address t h e "time problem" in geology were historically spurred by two quite different motives. T h e first began as essentially a religious pursuit but later became t h e most pressing scientific, question of the late n i n e t e e n t h century. Learned m e n (mainly theologians) were curious about the age of the earth and h o w t h a t age was related to t h e myriad myths of the creation. T h e second prod was far more prosaic. Early geologists found that they could more easily find economically valuable minerals and fuels if they could understand t h e structure of t h e earth's surface. Very quickly, they realized they needed some way to date rocks. T h e r e has certainly been no lack of effort to answer these questions. Finding the age of t h e e a r t h was a quest long entrusted to theologians, w h o searched n o t in t h e crustal record of t h e e a r t h itself but a m o n g the sacred writings of h u m a n prophets. T h e i r answers varied b e t w e e n a few t h o u s a n d years and infinity. T h e H i n d u tradition weighed in at slightly less t h a n 2 billion years, whereas some Hebrew and C h r i s t i a n calculations yielded values of less t h a n 10,000 years. But as technology advanced, and t h e thirst n o t only for religious understanding but also for metals and fossil fuels increased, measurement grew more scientific. W i t h the onset of the Industrial R e v o l u t i o n , k n o w i n g the age of rocks became a necessary prerequisite to finding industrial minerals, such as coal, iron, and the o t h e r materials t h a t fueled and sustaining t h e great Western industrialization of the e i g h t e e n t h and n i n e t e e n t h centuries. It was in the mining regions where engineers, w h o needed a better system for organizing 5

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the chaotic piles of rock slung across t h e earth's surface, first grappled with scientific approaches to understanding t h e age of any r o c k — a n d the age of the earth. T h e y realized that if t h e various rock units could he dated by their relative ages, correlations a m o n g e v e n widely separated rocks could be established and, from this, some order recognized in t h e geological chaos that is t h e crust of t h e earth. But how could rocks be dated? T h e pioneering European geologists first believed that identifying a rock's type would give t h e m a strong clue to t h e age of t h e rock formation and t h a t o n e of t h e most powerful clues c a m e from t h e hardness of a given rock. Specific rock types were thus assumed to h a v e formed at characteristically different times, the softest rocks h a v i n g formed the most recently. T h i s crude type of dating was first used to understand t h e way m o u n t a i n s were formed. In t h e mid-1700s it was t h o u g h t t h a t t h e r e were three distinct types of m o u n t a i n s in Europe, each formed by a different type of rock and each created at a different time. A c c o r d i n g to this theory, t h e oldest were the Alps, which had interior cores composed of very hard, crystalline rocks (such as granite, schist, or basalt). T h e s e m o u n t a i n s were called Primitive. Sitting on the flanks of t h e Primitive m o u n t a i n s were younger Secondary m o u n t a i n s composed of layered sedimentary rocks such as limestone, often rich with fossils and intermediate in hardness. T h e youngest Tertiary m o u n t a i n s were composed of softer mudstones and sandstone also rich with fossils. T h e s e formed low hills rather t h a n true m o u n t a i n s . Rock type and hardness thus established m o u n t a i n type, and rock type also became a proxy for age. H o w wonderful it would h a v e b e e n for scientists if indeed t h e earth were so simply organized! Yet how disastrous for my profession! T h e r e would h a v e been no work for t h e legions of bickering geologists w h o , it turns out, h a v e had to do t h e real work of discerning t h e age of rocks. Study soon exposed t h e fallacy of these early n o t i o n s . It was discovered t h a t some of t h e very high m o u n t a i n s were composed of t h e softest sediments and t h a t very hard volcanic rock was sometimes found in very low m o u n t a i n s . By the early 1800s, it was understood that rock type was of little or no h e l p in establishing either t h e form or the age of a m o u n t a i n and that a rock's composition, or mineral c o n t e n t , is virtually i n d e p e n d e n t of age. 6

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Geologists were in despair until a way was found to tell t h e age of at least some types of fock: t h r o u g h t h e use of fossils. Odd things, fossils. Long k n o w n as curios, they b e c a m e the most cutting-edge scientific tools in t h e Europe of t h e Industrial Revolution, for it was discovered t h a t with fossils, t h e relative ages of geographically separated rock bodies could be deduced. M a n y of us recall being fascinated by fossils as children, but they are serious tools of paleontologists e v e n in our d a y — anachronisms still useful in this age of instrumental extravagance. S o m e of us have never put t h e m away with t h e o t h e r wonders of c h i l d h o o d .

T h e first time S t e p h e n Jay G o u l d has written of his paleontological e p i p h a n y w h e n he first encountered t h e A m e r i c a n Museum's colossal Tyrannosaurus rex skeleton. Mine was a more modest fossil discovery, m a d e on a seashore t h a t n o w exists in memory alone. In W a s h i n g t o n state t h e strongest weather, like t h e strongest light, comes from the south, t h e direction from w h i c h great w i n t e r storms arise. Beaches, created and m a i n t a i n e d by weather, thus take on t h e personality of the directions in w h i c h they face. S o u t h e r n b e a c h e s carry t h e largest wrack, the finest sand, t h e biggest boulders. W e s t e r n a n d eastern beaches are calmer, yet still p r o n e to v i o l e n c e . N o r t h e r n beaches are t h e rarest a n d , like t h e n o r t h e r n light and n o r t h e r n sea t h a t b a t h e t h e m , t h e most c o n stant. A long gravel heach claims the n o r t h e r n shoreline of Orcas Island. Looking n o r t h , there is only a view of largely or utterly deserted islands, mostly C a n a d i a n . O n e of these is Sucia Island, w h i c h from my family's vacation cabin on the n o r t h e r n shore of Orcas indeed looks like a low battleship. We children, brought up on patriotic World W a r II war movies, sank it innumerable times with imaginary torpedoes. It n e v e r moved. Easy shot. T h i s patticulat gravel beach was a biological paradise at low tide. Early morning was our favorite time for c h i l d h o o d b e a c h exploration, and we 7

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searched only for sea creatures b e n e a t h t h e cobbles and boulders of the intertidal. T h e rarest treasures were small eels living in the tide pools. Rocks were n o t a priority. Life was. But o n e rock caught my a t t e n t i o n , in these last years of President Eisenhower's rule, as I h e a v e d it over to unveil t h e c a c h e of scurrying beach crabs b e n e a t h . Football-sized, gray, and rounded, this particular rock was absolutely packed with clamshells. Finding clamshells was no revelation, for shells in no small n u m b e r littered t h e beach, but t h e r e was a major difference h a v e : T h i s rock was filled with shells turned to stone. A l t h o u g h some of the more far-fetched fairy tales of c h i l d h o o d dealt (in simpler terms) with such issues as lithification, I was by no m e a n s so unsophisticated. T h i s rock was clearly filled w i t h fossil shells, and with whoops and hollers I alerted the rest of my family. A week later, a local r o c k h o u n d confirmed this find as indeed being b o n a fide fossil material and e v e n put a n e w spin on t h e stony clamshells. N o t only were they fossils, but they were old—Mesozoic in age, he said. Mesozoic was a key word for an eight-year-old; Mesozoic was t h e time of the dinosaurs. I had found a rock with clams in it t h a t had sat on that beach since t h e time of t h e dinosaurs, or so 1 divined from all of this disparate information. Yet t h e b e a c h from w h i c h it c a m e had no rock o t h e r than' gravel and was n o t t h e source of this fossil. It had c o m e from t h e north, perhaps from Sucia, or m i g h t e v e n h a v e b e e n carried across t h e International Boundary during t h e Ice Ages 12,000 years ago w h e n t h e first C a n a d i a n s were eating the last of their woolly m a m m o t h s . T h e rockhound's lair was a place of wonder. He had a tumbling wheel, rock saws and polishing laps, and of course rocks of all sizes and shapes littering dusty shelves. But he was also a person of some learning, and he had t h e gift of patience in dealing with i m p a t i e n t youngsters. For my part, I had made a find. I basked in glory. I asked questions. A n d inevitably I asked the most c o m m o n question about rocks and fossils: H o w do you know how old this rock is? He had a very difficult time answering t h a t question in any sort of direct manner. He could only say t h a t t h e clams I had found were n o w extinct 8

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but had lived in t h e Mesozoic Era. H o w many years ago was that, I asked. Hundreds of millions, he s o m e w h a t uncertainly replied. "But h o w do you know? H a v e these rocks ever been put in some m a c h i n e t h a t tells theit age?" G o n e now was his confidence, and 1 knew he was on shaky scientific ground. He lost patience with me, and my father and I soon left. 1 had discovered many small truths t h a t day and o n e m u c h larger one: Divining the age of a rock can be very difficult. Years later, I would be asked the same question i n n u m e r a b l e times and, like t h e r o c k h o u n d of my youth, would never be able to give a short, satisfactory e x p l a n a t i o n . T h e r e is no short explanation. T h e r e is no magic box t h a t , w h e n placed over some dusty relict of our planet's tumultuous and seemingly ageless past, displays some shining number. It is not t h a t we do n o t h a v e m a c h i n e s t h a t give ages. It is just that such machines work only on a very small suite of rock types—and even t h e n only on an smaller subset of those rocks t h a t h a v e lain relatively undisturbed for great swaths of time. A n d tranquility is a very tare t h i n g on this planet's everywhere-disturbed surface.

C h a n c e and t i m e C h i l d h o o d fossils are usually left b e h i n d on yellowing shelves. For some of us, however, they are never left b e h i n d . I could never put t h e m away. T h e y were transfigured from curio to curiosity. In 1971 I became a graduate s t u d e n t in paleontology. I wanted to study fossil whales, but a c h a n c e e v e n t soon steered me toward a m u c h older past, the Mesozoic-aged life and times of a n c i e n t Sucia Island. M u c h of my school work in that first year involved t h e study of stratigraphy ( t h e geological discipline concerned with a n c i e n t time) and anatomy. But I learned as m u c h from constant scuba diving as I did from classes at t h e university. I learned about the communities of organisms living in Puget Sound, w h o ate w h o m , and how these c o m m u n i t i e s of invertebrates are distributed in space and time. I watched as sedimentary beds formed under t h e sea. I witnessed t h e slow burial of dead shells and bones, whose long journey toward fossildom was just beginning. Every dive was a new exploration, and with every dive I

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imagined what different versions of the past and its c o m m u n i t i e s may have looked like. I saw each dive as a key to unlock t h e past. In February I a c c o m p a n i e d a group of new divers on a particularly cold day. We were working off t h e west coast of S a n Juan Island, in some of the most beautiful waters in all of t h e Americas. T h e huge inland sea called Puget Sound, c o n n e c t e d to t h e Straits of George in C a n a d a , is o n e of the most diverse (and coldest) underwater regions on earth—diverse in terms of b o t h the animals and plants present and t h e various types of terrain t h a t can be e n c o u n t e r e d . We waded in from t h e beach. T h e dive was to be into rocky scallop beds at 50 feet or more. We shivered at water's edge, eager to get in, for this was o n e of t h e rare days w h e n t h e water was warmer t h a n the air around us. We looked like a flock of lugubrious penguins, shiny in our dark n e o p r e n e wetsuits, shuffling awkwardly in t h e massive e q u i p m e n t . W h e n all was ready and I h a d absorbed t h e first shock of t h e frigid water against my skin, I replaced snorkel with regulator m o u t h p i e c e , drew a first metallic taste of compressed air, a n d headed d o w n . We passed first over gravel, t h e n over bedrock showing the distinctive intertidal zonations of this region (barnacles followed by a mussel zone), and finally into t h e subtidal, where a far greater diversity of marine life greeted us. We c o n t i n u e d downward, m o v i n g over t h e festooned rocky bottom, passing t h r o u g h p e n n a n t s of green and red kelp while armies of sea urchins waved their spiny pikes at our passing shockwaves. At last we entered the zone rich in scallops, first e n c o u n t e r e d about 30 feet down, our fins creating turbulence t h a t sent these bizarre mollusks swimming like so many wildly clacking false t e e t h in a bad c a r t o o n . T h e water became clearer and colder, but calmer as well, t h e world of air and surface and all m a n n e r of that life edging away, and I felt exhilarated. I watched, and studied, and noted the relationship b e t w e e n d e p t h and t h e type of animals present, n o t knowing at the time t h a t I was laying t h e foundation for understanding o n e of the most important of all paleontological principles: t h a t water d e p t h can be inferred from t h e type of fossils present in a sedimentary section. Using the present to

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understand the p a s t — t h e principle of uniformitarianism—is o n e of t h e most powerful of all time m a c h i n e s . All too soon it was over. Air exhausted, our small group of divers retreated again to our native land. After the dive I chatted with one of the other divers, and he asked the usual questions of a stranger, including the inevitable " W h a t do you do?" I told him that I was a beginning graduate student in paleontology and had been assigned to study whale fossils from the Washington state seacoast. T h e only trouble was that despite arduous searching, I had yet to find .1 single whale fossil and w a s rapidly getting discouraged. T h e man told me that he was an amateur paleontologist. He had never looked for whales, but he had been collecting fossils from Sucia Island for many years and had a large collection that he would give me if I wished. Apparently, I had reached a fork in my career p a t h — o n e direction leading to the study of the Cenozoic Era and its whales, the other leading back into deeper time, toward the Mesozoic Era and its ammonites, nautiloids, and dinosaurs. On that day I took t h e latter route. My new friend was as good as his word. W i t h i n a week an e n o r m o u s collection of fossils, all meticulously cleaned, n u m b e r e d , and their collection locations noted (in short, all t h e hardest work d o n e ) , arrived in my tiny cubicle of an office. Nearly all fossils resembled t h e modern-day nautilus but were far more ornate. T h e y were fossil a m m o n i t e s , e x t i n c t relatives of the chambered nautilus and t h e first I had ever seen apart from t h e poor, scrubby examples in our classroom t e a c h i n g set. T h e a m m o n i t e s from Sucia are iridescent, large, exquisite. T h e y and their k i n d — I t h o u g h t t h e n — a r e also akin to a n c i e n t stone wrist watches. All I had to do was look in some book and identify t h e species of a m m o n i t e s from Sucia Island, and I would find t h e age of the sediments where they had b e e n collected. W h a t could be easier? T h e fossils all had numbers and could be keyed into a m a p . But k n o w ing the geographic position of e a c h fossil-collecting locality was n o t e n o u g h for me to come up with any sense of age. T h e i r stratigraphic position was what I needed. Stratigraphy is t h e study of layered rocks and of t h e relative ages of strata. Nearly all fossils c o m e from layered rocks, and e a c h layer in a sedimentary succession sits upon o n e slightly older. Because Sucia is made up of

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many such layers, I needed to k n o w n o t only where on the island the fossils came from hut also from what sedimentary level they had been collected. W i t h o u t k n o w i n g this, I was duplicating t h e faulty way European geologists first tried to use fossils to tell t i m e in t h e late e i g h t e e n t h and early n i n e t e e n t h Century. For a fossil to be of use, o n e must know its position in strata relative to o t h e r fossils: Is it from a higher or lower stratum or from a stratum of the same level? T h e genius of t h e first geologists, in t h e late 1700s, was their recognition t h a t higher m e a n t younger, lower m e a n t older, and fossils found at t h e same level were about t h e same age. T h e s e observations became the first law of t h e new science of stratigraphy and were codified into the law of superposition of fossils. I had to place t h e Sucia Island fossils t h a t had been donated in the context of t h e stratal bedded layers found on Sucia itself. T h e r e was only one solution. I c o n v i n c e d several o t h e r graduate students w h o were studying paleontology at my U n i v e r s i t y — a n d my academic advisor—that a winter trip to Sucia Island was a wonderful idea, a lark, a challenge, an adventure, a scientific necessity ( t h e story c h a n g e d to fit t h e person whose arm was being twisted). Blackened highways led from Seattle in t h e rain, t h e short day soon giving way to night. We spent t h e first night in a small cottage on Orcas Island, facing Sucia. Arising and breaking fast in predawn cold and dark, we set out for Sucia with a borrowed boat and a dubious outboard engine on a steel gray dawn, leaving t h e coast of Orcas Island b e h i n d in the mist; soon it was lost to view. I was a s u m m e r i n h a b i t a n t of these islands, and the reality of winter here was a shock. G o n e were t h e lazy clouds and azure sky. G o n e was t h e placid green sea. We set out in a wild winter ocean of froth and charging herds of w h i t e n e d waves, an overloaded boat filled with foolish scientific zealots in search of fossils on a faraway island, cloaked in t h e invincibility of youth. Halfway across t h e two-mile stretch of o p e n sea, t h e motor quit and we literally rowed for our lives, barely keeping t h e boat from swamping in t h e frigid waters. I could see t h a t my professor was livid at having been talked into coming on such a journey in winter, and it was only the prevailing south wind t h a t blew us to Sucia and safety. 12

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We arrived on t h e dark shores soaked and frightened, c o n d u c t e d repairs to ensure our return at t h e e n d of t h e day, and t h e n in sodden misery set out to accomplish at least s o m e t h i n g , trudging along t h e gravel p a t h in wretched, squeaking hoots. We students t h o u g h t we k n e w what to do; we had read articles and t a k e n classes. Yet our knowledge ahout h o w actually to wrest any information from these rocks was nil; we were enthusiasts, n o t geologists. We wete like the nascent "geologists" of t h e late e i g h t e e n t h century who knew that fossils had to be of scientific importance but h a d no idea h o w to access the information they held. My professor took charge, quoting from the work of the ghostly forefathers of geology, i n t o n i n g t h e odd n a m e s t h a t were becoming increasingly familiar to us: the Englishman William S m i t h ; the French, Alcide D'Orhigny and Georges Cuvier; t h e G e r m a n s , A l b e r t Oppel and Friedrich Q u e n s t e d t . He spoke of stratal succession and fossil succession, the law of "superposition of strata," and t h e time units called stages and zones. But he always teturned to o n e m a n t r a : Faithfully sample t h e fossils ftom "measured sections." Measure t h e strata. C o l l e c t t h e fossils from measured sections. He began to guide us t h r o u g h this thick maze of rock. "Start by measuring the sections," he kept repeating. O u r impulse was to collect the fossils immediately, w h i c h is what children do. "First, describe in your notebooks t h e nature of t h e rocks while you measure their thickness, and then collect t h e fossils, always n o t i n g their exact location b o t h geographically and stratigraphically. Unless you k n o w the relative positions of the fossils, they are useless." My professor had been trained by Europeans. He knew that fossils could tell time only if their relative positions in t h e succession of strata could be determined. We set out to do this, long measuring tapes in h a n d , desctibing t h e strata as best we could in our yellow field n o t e b o o k s and recording the position of the fossils as we came upon them. A m m o n i t e , field number 12/27/71-3, identity u n k n o w n , from thick limestone layer located 25 meters above t h e base of the section, geographic location 200 yards n o r t h of m o u t h of Fossil Bay." We used compasses to learn t h e " a t t i t u d e " of t h e beds, measuring the degree of tilt that the strata had undergone; we proudly urinated on t h e rocks as we had been bidden, watching these rivulets flow d o w n t h e line of the 1;

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rocks' true dip. Tricks of t h e trade. Shrouds of rain billowed downward in this time before Gore-Tex; t h e tall firs overhead seemed dismally somber, and the summer joy of fossil collection n o w seemed grimmer, more fitting for adults, no longer a c h i l d h o o d delight. L u n c h was a water-logged p e a n u t butter sandwich and a c a n of C o k e , t h e sugar and caffeine a welcome lift. We worked with stolid, grim purpose, and I sympathized with t h e long-ago pioneers who had first c o n c o c t e d this methodology. As t h e day wore on, a c o l u m n of strata began to form in our notebooks, and a checklist of fossils from various levels in t h a t c o l u m n was recorded as well. Fossil prizes were few. Up until now I had always scoured Sucia for the fossil prizes, eschewing all save t h e most pristine fossils. N o w every scarp was information, every scrap of long-dead shell a d a t u m point if its identity could be ascertained. T h e grubby fossils were chiseled out of the strata in the fine rain, later to be labeled and wrapped. T h e day flew by; it was time to try to return to Orcas Island in t h e small boat, a voyage I dreaded. I was surprised at h o w little o n e could do in a day. I was surprised t h a t it was no longer play but work. But we had indeed collected data, a n d for t h e first time I understood responsibility to record faithfully. " G o o d data are immortal" read a sign on an office wall at our school. But data could be "bad"—mislabeled fossils, poor measuring, poor recording. We had t a k e n a small measure of Sucia's secrets, its long-held mysteries. A n d in so doing we had proudly applied exacting scientific methodology. Later t h a t night, safely back in our cabin on Orcas Island, we shared our notes, shared a welcome warm dinner, shared a sense of profession. T h e professor w a t c h e d over t h e apprentices with satisfaction as they drank t h e m selves into stupor, a n o t h e r geological tradition. Later t h a t week I extracted from my still-soggy field notebook the measured section we h a d made and drew a c o l u m n of the strata, arranged with t h e oldest layers on t h e b o t t o m , t h e youngest on top. T h e n I portrayed in graphical fashion t h e positions of t h e a m m o n i t e s earlier collected, as well as those found on this trip. Each fossil was identified as a given species and plotted on t h e chart, t h e first appearance and t h e last appearance of each "taxon," or species, being n o t e d with a bold line. S o o n a series of short and 14

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long lines were arrayed beside the c o l u m n of strata. S o m e fossils were k n o w n from many specimens, some from a few or e v e n a single o n e . Clearly, some of the ammonites had b e e n very c o m m o n , whereas some were m u c h more rare. Ten different species seemed to be present. It was a start.

F o s s i l s and " b i o c h r o n o l o g y " A very practical Englishman n a m e d William S m i t h was t h e first to show that fossils could provide a practical system for dating rocks. Nearly two c e n turies before our winter visit to Sucia Island, S m i t h was t h e first to formalize the system of stratigraphic collecting t h a t all paleontologists would ultimately use. William S m i t h was an English surveyor working on the e x c a v a t i o n of the British inland canal systems in t h e late e i g h t e e n t h century. He was present as these great canals were cut t h r o u g h t h e local rock, and thus he observed firsthand the t r e m e n d o u s numbers of fossils t h a t c a m e from t h e fresh cuttings. He began keeping records about t h e types of fossil he saw, and he eventually realized t h a t he was seeing t h e same succession of fossil types in different regions. M a n y naturalists prior to S m i t h had recognized t h a t fossils from a lower succession of strata were often different from t h e fossils found in younger, overlying strata. But no o n e h a d noticed t h a t t h e succession of fossils in strata was often t h e same from region to region. T h i s stroke of genius enabled S m i t h to "correlate" strata in widely separate geographic regions of his country. H o w did the same succession of fossils c o m e to be deposited in strata? S m i t h was an engineer, n o t a scientist; he really didn't care h o w t h e fossils he found came to be present in t h e rocks. To h i m they were simply tools to be used. In almost every case, t h e fossils he used were petrified shells called ammonites. Smith's great discovery was n o t immediately k n o w n beyond his working-class circle of acquaintances. Indeed, his discovery was first announced in a pub. S m i t h was n o t a " g e n t l e m a n , " so it was many years before his discovery was published and word of it disseminated. S m i t h , w h o had had 15

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little formal schooling, found writing difficult and searched for a n o t h e r way to illustrate his results. He hit u p o n t h e novel idea of publishing a m a p of geology, n o t geography. Each region of differently aged rock was accorded a different color on his map, a ptactice still in use today. S m i t h , in constructing the first geological map, produced o n e of the first time machines, for his mapping of strata became o n e of t h e earliest and most accurate ways of studying a n c i e n t time. Smith's life's work, t h e first geological m a p of England, was published in 1815. It was a revolutionary d o c u m e n t and, like many such advances, was little noticed for m a n y years. S m i t h himself received little recognition for his discovery in his lifetime. Yet gradually word of this new tool did spread, and by t h e second decade of t h e n i n e t e e n t h century, many geologists began to realize what S m i t h had long k n o w n : Rocks could he formed at any time in earth history, but fossils could n o t . Limestone could be formed at any time, but limestone c o n t a i n i n g a m m o n i t e fossils could be no younger t h a n the Mesozoic Era. Here, t h e n , was t h e new tool. You could n o t d e t e r m i n e the actual age of a rock, in t h e sense of age as we k n o w it. Even with a fossil, you could never identify a rock as being so many hundreds, or thousands, or millions of years old, and indeed no societies of t h e time could make any accurate estim a t e about h o w old t h e earth and its rocks were. But you could quite accurately d e t e r m i n e w h i c h rock was younger and which older, and this made it possible to u n d e t s t a n d and m a p t h e structure of t h e earth's surface and, in so doing, discover its underground secrets and mineral treasures. T h e use of fossils as relative indicators of time was soon taken up by geologists all over t h e European c o n t i n e n t . Major units of time were based on the unique fossil assemblages t h a t were characteristic of t h e m . T h e s e subdivisions, t h o u g h originally based on actual rock bodies, became de facto units of time. For instance, an English geologist n a m e d A d a m Sedgewick spent several summers in t h e early part of the n i n e t e e n t h century studying strata found in Wales. T h e s e rocks showed t h e transition between lower strata devoid of fossils and overlying strata filled with fossils—the transition we now know to mark t h e start of t h e Paleozoic Era. Sedgewick n a m e d the fossilifer16

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ous rocks the C a m b r i a n System and used, in his definition of this group of rocks, t h e characteristic fossils enclosed and found w i t h i n these strata. T h e C a m b r i a n Period was denned, t h e n , as t h e block of time during which these s t r a t a — t h e C a m b r i a n System—were deposited. W e now k n o w t h a t the C a m b r i a n Period started about 530 million years ago and e n d e d about 500 million years ago. A l t h o u g h Sedgewick's strata are found only in a small part of Wales, we refer to all rocks on e a r t h as belonging to t h e C a m b r i a n System if it can be demonstrated, t h r o u g h fossil c o n t e n t or some o t h e r technical means, t h a t they were formed b e t w e e n 530 and 500 million years ago. ( T h e assignment of ages in years to various geological units of time is a t w e n t i e t h century advance, as we will see later in this chapter.) Even larger-scale divisions were soon recognized—defined by mass extinction events, w h i c h are sudden global catastrophes causing major biotic turnovers and e x t i n c t i o n . Two of these were especially d r a m a t i c . At t h e top of strata n a m e d t h e P e r m i a n System, a n d again at t h e top of a m u c h younger group of strata k n o w n as t h e C r e t a c e o u s System, t h e vast majotity of animal and plant fossils was replaced by radically different assemblages of fossil. N o w h e r e else in t h e stratigraphic record are such abrupt and allencompassing changes in t h e faunas and floras found. T h e s e two wholesale turnovers in the makeup of t h e fossil record were of such magnitude t h a t t h e Englishman J o h n Phillips used t h e m to subdivide t h e geological time scale into t h t e e large-scale blocks of time. T h e Paleozoic Era, or "time of old life," e x t e n d e d from t h e first a p p e a r a n c e of skeletonized life 530 million years ago until it was e n d e d by t h e gigantic e x t i n c t i o n of 250 million years ago. T h e Mesozoic Era, or "time of middle life," began immediately after t h e great Paleozoic e x t i n c t i o n and ended 65 million yeats ago with T h e Cenozoic Era, or "time of new life," extending from the last great mass e x t i n c t i o n ( t h e " K / T event") to t h e present day. A hierarchical assemblage of units was thus established, e a c h based on actual rocks and t h e fossils they c o n t a i n e d . T h e largest-scale units were t h e eras defined by t h e mass e x t i n c t i o n s . T h e s e eras were in t u r n m a d e up of the systems and their a c c o m p a n y i n g periods, such as t h e C a m b r i a n and the Jurassic. Yet these units were also quite large in scale and were surely of long 17

Fossil ammonite cephalopods from Cretaceous Age strata, France.

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duration. A subdivision of t h e periods was needed to refine geological study. T h e r e had to be a smaller-scale unit of time t h a n t h e periods—a unit recognizable all over t h e earth. S u c h a unit was discovered by a French geologist working in the white chalks of Mesozoic age t h a t are so characteristic of n o r t h e r n Europe, rocks ultimately n a m e d t h e C r e t a c e o u s System. T h e great white chalk formations stretching from England across t h e length of n o r t h e r n Europe were well k n o w n to all of t h e early geologists, and surely to the earliest h u m a n s in Europe as well, for t h e chalk yielded t h e most important of all Paleolithic tool materials, flint. William S m i t h himself knew these formations well, for m u c h of s o u t h e r n England is m a d e of chalk, and his canals were cut t h r o u g h endless miles of t h e white rock. S m i t h recognized two units in the c h a l k — o n e greenish a n d sandy, t h e o t h e r more rich in clay. Similar units could be traced beyond England, a n d in 1822 D ' O m a l ius d'Halloy completed an extensive study of t h e chalk in France, w h i c h he named the Terrain Cretace, or t h e C r e t a c e o u s System. S o o n o t h e r workers had added to the understanding of t h e C r e t a c e o u s System. French geologists discovered t h a t m a n y of t h e fossils first extracted from the chalk in England were also present in France. T h i s discovery convinced some naturalists that t h e same fossils e x t e n d e d everywhere on earth. A French naturalist n a m e d Alcide d'Orbigny became c o n v i n c e d of this and, using a m m o n i t e fossils, subdivided t h e Cretaceous System into many smaller units. He named these stages. T h e actual basis for any stage was a fossil aggregate that was unique to it. He was sure t h a t his units allowed t h e subdivision of time and t h a t they were recognizable all over t h e world. Indeed, 150 years later, geologists still use b o t h t h e term and t h e c o n c e p t . T h e stage today is recognized as t h e most refined subdivision of s t r a t a — a n d t i m e — t h a t is worldwide in e x t e n t . T h e various stages defined by A l c i d e d'Orbigny were first recognized in southwestern France. Fossils defined t h e m , n o t rock type, yet by c h a n c e each had a slightly different rock type t h a t supported a slightly different type of wine grape. T h e stages were n a m e d after t h e regions where they were first recognized, and some familiar n a m e s exist: t h e C o n i a c i a n Stage, n a m e d after

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Historical development of Geological Time scale from 1790 to Modern Age.

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the C o n y a c region; t h e C a m p a n i a n Stage, n a m e d after t h e C h a m p a g n e grape region. You could m a p t h e stages by t h e wine grapes growing in t h e i t soils. All of the great French vintages w e r e — a n d are still—nurtured by t h e skeletons and eroded fossils of Late C t e t a c e o u s forms in France. T h e first glimpse of these strata is b r e a t h t a k i n g . T h e best place to view t h e m is along a series of cliffs lining t h e G i r o n d e estuaty just n o r t h of Bordeaux, where t h e gleaming, eye-assaulting whiteness of pure chalk and limestone dominates the landscape. T h e s e strata are completely different in appearance from the drah gray a n d green siltstones and shale of t h e Vancouver Island region, yet they are rocks of t h e same age, visions in alabaster rather t h a n olive. For many years Alcide d'Orbigny described and collected from these gleaming white strata, eventually c o n c l u d i n g t h a t his "stages" were worldwide units. But were D'Orbigny's stages actually worldwide in extent? He certainly t h o u g h t so, noting, " T h e stages are t h e expression of t h e divisions which nature has delineated with bold strokes." Like t h e great naturalist C u vier before him, D'Orbigny was a confirmed catastrophist. He believed t h a t the assemblages of fossils he recovered from his stages wete created by some Supreme Being, lived for a short time, and t h e n were destroyed by a worldwide catastrophe. Accordingly, they would work extremely well as worldwide time lines in sedimentary rocks. Enthusiasm and a little knowledge (but n o t too m u c h ) reigned in t h e middle of the n i n e t e e n t h century. By t h e 1860s t h e framework of t h e geological time scale was complete; the major subdivisions, identifying characters, and type regions had b e e n defined. Yet so little detailed work had yet been d o n e t h a t it was optimistically assumed t h a t assemblages of fossils first recognized in England, and later found in France and Germany, would be found the world over. Legions of European geologists streamed outward from their s u b c o n t i n e n t , sure t h a t t h e fossils n o w so well k n o w n in Europe would be found everywhere and could be used to assemble all sedimentary strata into what was becoming a European standard of time. But disillusionment soon set in. T h e farther from their o w n field areas t h e geologists ventured,

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the fewer familiar fossils they found. Instead they began to find new, unrecognized species intermixed with t h e m o t e familial fotms of t h e h o m e country. Finally, if a distant e n o u g h voyage was u n d e r t a k e n (such as to Africa or to t h e Far East), almost no co-occurring fossils were apparent. By the time those practicing t h e newly developed science of geology teached t h e west coast of N o r t h A m e r i c a , no European fossil species of any kind could be found. H o w could time lines be discovered without similar fossil species? T h e discovery of fossils in western N o r t h A m e t i c a in t h e 1860s put the m e t h o d s of t h e European geologists to their most severe test. Progress in mapping t h e vast c o n t i n e n t of N o r t h America, especially its western portions, was excruciatingly slow. T h e travel alone was punishing; t h e r e were no stores nearby for provisions, no c o m m u n i c a t i o n s , no support of any kind in t h e e v e n t of accident or sickness. A n d t h e expenses of mapping geology in a n e w and still-poor country were prohibitive. N e v e r t h e less, various g o v e r n m e n t authorities saw t h e need for accurate geological maps, especially in light of t h e spectaculat gold and mineral finds t h a t had recently b e e n made in California and elsewhere. In 1860, t h e California state legislature created an Office of S t a t e G e ology and authorized t h e formation of a geological survey for t h e state. T h u s , while t h e Civil W a r raged on t h e o t h e r side of t h e c o n t i n e n t , a small band of scientists began t h e immense task of c o m p l e t i n g " A n A c c u r a t e and C o m plete Geological Survey of t h e S t a t e of California," w h i c h was intended to c o n t a i n "a full and scientific desctiption of its rocks, fossils, soils and minerals and of its botanical and zoological productions." Perhaps never has a geological survey b e e n so widely defined. T h e n e w survey began its work with "greater or less vigor, according to t h e varying a m o u n t s appropriated hy each successive Legislature." T h e m a n put in charge of paleontological study was a Mr. W. M. G a b b . T h e first discovery of Cretaceous-aged rocks in California was made just east of t h e Bay Area, in t h e region of M o u n t Diablo, in 1861. By describing these rocks as Cretaceous, G a b b was stating t h a t t h e thick mudstones and sandstone in t h e Mt. Diablo area were of t h e same age as the sepulchral chalks lining t h e English C h a n n e l . T h e r e could n o t be two more 12

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dissimilar sedimentary rock types. G a b b , however, made this correlation on the basis n o t of rock type but of fossil c o n t e n t . B o t h t h e European and t h e Californian rocks had o n e aspect in c o m m o n : the presence of fossils particular to and diagnostic of t h e Cretaceous System as it was originally defined. These fossils were t h e a m m o n i t e s , t h e group William S m i t h h a d spent so m u c h time studying in t h e late 1700s a n d t h a t d'Orbingy used so successfully in the mid-1800s. A m m o n i t e s were a m o n g t h e fastest-evolving creatures ever to h a v e graced t h e earth, and individual species are thus diagnostic of relatively short intervals of earth history. Cretaceous a m m o n i t e s differ from those t h a t came earlier by their highly o r n a m e n t e d shells, often uncoiled shapes, and very complicated septal sutures ( t h e shell j u n c t i o n s uniting their shell walls with the c h a m b e r walls, or septa). By 1862 the small survey crew had moved i n t o t h e G r e a t Valley of California and began surveying and excavating along t h e eastern flank of t h e m o u n t a i n s k n o w n as t h e Sierra N e v a d a . Deep in creek b o t t o m s already pillaged by the gold miners of a decade earlier, they found sandstone and mudstone rich in fossils. G a b b found a m m o n i t e s in a b u n d a n c e , t h e most comm o n being a straight a m m o n i t e called Baculites. On two tributaries called C h i c o C r e e k and Butte Creek, these fossils were present in untold numbers, preserved in a fashion superior to any from Europe, for t h e dusky mudstones of California had protected t h e fossils from ground water and erosion. T h e i r iridescent shells gleamed red and green as G a b b and his crew exposed t h e m to California sunshine for t h e first time since t h e Mesozoic Era. G a b b and his crew discovered t h a t t h e Cretaceous System was widespread not only in California but along t h e entire Pacific Coast as far n o r t h as C a n a d a . In 1863 G a b b took time away from his California work and traveled through O r e g o n and W a s h i n g t o n to V a n c o u v e r Island, where he collected fossils in many localities. His conclusion was t h a t m a n y of t h e same species he had already e n c o u n t e r e d on C h i c o C r e e k could be found in t h e Vancouver Island region as well. By the time t h e first Geological Survey of California had finished its initial four-year charter, it had collected thousands of fossils; and in 1864 it 23

Illustration of ammonite shell from Gabb's first publication concern the Cretaceous fossils of California.

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published its first description of these fossils, a massive t o m e describing 260 species all new to science. N o t a single o n e of these species was k n o w n from anywhere to t h e east, including Europe! T h e C r e t a c e o u s System ( t h e largescale time unit defined by Sedgewick and others) could be recognized, hut the Cretaceous stages ( t h e smaller-scale units of d'Orbigny and others), all based on a m m o n i t e s from Europe, could n o t . T h e s e findings put an end to D'Orbigny's dream t h a t his stages would be recognizable and useful all over the world. T h e Californian work of G a b b showed t h a t only t h e most approximate sort of correlation could he found. More t h a n a century later, this situation

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fofaminiferans, a type of free-floating amoeba w i t h a shell, o n e could roughly recognize the European stages on t h e Pacific C o a s t . M a n y uncertainties remained w h e n a new generation of paleontologists re-examined t h e rocks and fossils of California, W a s h i n g t o n state, and western British C o l u m b i a in t h e middle of the t w e n t i e t h century.

Time after time T h e pioneering European geologists had made two great discoveries t h a t are still useful today: (1) T h e most accurate way to understand t h e geometry of various rock bodies on t h e earth's surface is to m a k e a m a p of t h e m , a n d (2) the best way to disentangle t h e relative ages of various sedimentary rock units is to collect and study their enclosed fossils. T h e scientific study of the Sucia Island region required b o t h . T h e collections of fossils made by many paleontologists over almost a century had yielded a good idea about Sucia Island's cast of a m m o n i t e s and their stratigraphic positions on t h e island. But t h e Sucia strata are but o n e slice of the m u c h thicker stratal layercake found in t h e Vancouver Island region. W h e r e (stratigraphically, n o t geographically) in this 15,000-foot-thick pile of sandstone, shale, and conglomerate does Sucia sit? H o w does its age compate with that of the sedimentary rocks found on nearby islands, such as Orcas and Waldron? H o w does Sucia c o m p a r e in age with these and to with the more distant islands sprinkled around it? Sedimentary rock made up the 25

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entire region, but only from Sucia were fossils well described. S u c h was the problem facing me in 1972. My work in this region h a d put me in t h e same boat as William S m i t h so long before: S m i t h had collected fossils from a series of isolated canals snaking across t h e English countryside. But w h i c h fossils—and their respective canals—were older and w h i c h younger? H a d t h e English rocks been completely exposed (as in deserts w i t h o u t v e g e t a t i o n ) , he could have worked out t h e age relationships simply by following individual layers of rock across t h e countryside. But rocky exposures are t h e exception rather t h a n t h e rule in vegetated country like England, just as they are in my island country, where t h e o c e a n creates far more geological mystery t h a n even the trees. I h a d great thickness of strata, isolated by water and vegetation in many regions (around V a n c o u v e r Island), and I h a d a very imprecise knowledge of t h e age of these rocks and of h o w t h e various islands and isolated river canyons t h a t exposed rock were correlated o n e to another. It was necessary to do as t h e early Europeans h a d d o n e : spread out, m a p the various regions (islands and river canyons, in my case), and collect their fossils. T h e correct superposition of fossils, o n c e worked out, would serve as a guide to correlation. T h e succession of fossils b e c a m e t h e tool. O n c e I knew which a m m o n i t e followed which, I could apply this knowledge—just as S m i t h and D'Orbigny had d o n e — t o establishing t h e correct succession of rocks in the region. T h e most critical regions to study are those where two separate successions of fossils are in c o n t a c t — w h e r e o n e "zone" (based on a diagnostic assemblage of fossils) is directly overlain by another. T h e problem with Sucia was t h a t no such zonal c o n t a c t was exposed there; t h e same fossils were found in t h e lowest beds on Sucia as in t h e highest beds. O t h e r rocks had to be searched. Sucia was a "floating" section in t h a t it could still n o t be placed in t h e table of strata for t h e entire region. O t h e r nearby islands might hold the key. I needed a boat and so acquired my father's small a l u m i n u m fishing boat, 14 feet long with a 10-horse outboard. It was very slow. U n d e r perfect skies I began to ply t h e calm green waters, using Orcas Island as a base, and 26

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tadiated outward to ever more distant localities. T h e first stop was W a l d r o n Island, largely u n i n h a b i t e d and composed of great walls of massive sedimentary rock. On my first trip t h e r e I was struck by the difference in appearance between t h e fossiliferous rocks of W a l d r o n and those on nearby Sucia. T h e Waldron rocks were m u c h coarser-grained. T h i s was evidence t h a t they had been deposited in shallower water t h a n t h e rocks on Sucia. M a n y of t h e fossils were different as well. T h e r e were far more clams and snails t h a n on Sucia and far fewer a m m o n i t e s , two bits of evidence t h a t also attested to an origin in shallow water. T h e a m m o n i t e s t h a t were collected seemed to belong to species different from those on Sucia. But were the differences in fossils due to differences in time or to t h e fact t h a t t h e rock type was different? H e t e was a n o t h e r problem first discovered by t h e pioneering European geologists. Time was not t h e only variable t h a t affected fossil c o n t e n t . Most animals are adapted to living in very specific e n v i r o n m e n t s . D'Orbigny was t h e first to suspect differences in fossil c o n t e n t could sometimes be related to his sampling different e n v i r o n m e n t s , n o t to a different time of origin. Time units had to be i n d e p e n d e n t of e n v i r o n m e n t , but this is rarely t h e case, d'Orbigny and others found. S u c h was my problem with W a l d r o n Island. Day after day I motored to this island a n d collected fossils from its rocky cliffs. T h e work was wonderful: perfect temperatures, a b u n d a n t wildlife, no people. But t h e implications were troubling. As more and more fossils came to light, I was faced with three choices. W a l d r o n was older, W a l d r o n was younger, or W a l d r o n was t h e same age as Sucia, but because its rocks had been deposited in a different e n v i r o n m e n t , its fossils were different as a result of differences in ecology, n o t time. H o w to choose? T h e answer to this riddle was supplied by William G a b b , whose work was d o n e a century before mine. He had collected a species of a m m o n i t e from C h i c o Creek that turned out to be identical to those I found on W a l d r o n Island. T h i s a m m o n i t e , at least in California, was k n o w n to be older t h a n several species of a m m o n i t e s found b o t h in California and on Sucia Island. However, several other of the a m m o n i t e species t h a t I collected from Waldron Island were the same as those found on Sucia. T h a n k s to this particular correlation, I was able to propose t h a t W a l d r o n was slightly older t h a n Sucia. 27

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As t h e summer wore on, I studied o t h e r islands similarly. Rocks and fossils from t h e n o r t h shore of Orcas Island were discovered to be older t h a n those on W a l d r o n , and fossils on t h e n e x t island in t h e region I studied, a place called Barnes Island, were older yet. Rocks on t h e first of the nearby C a n a d i a n islands to t h e n o r t h of Sucia turned out to be slightly younger t h a n Sucia. By t h e e n d of t h e summer I h a d discovered t h e relative stratigraphic position of most islands in t h e region, just as William S m i t h had discovered t h e relative ages of his canals in England, and d'Orbigny the relative ages of the wine regions of southwest France. I could n o t assign the islands ages in millions of years. But for t h e first time, a table of strata could be assembled for this region. A n d with their relative ages, I could place the islands on a rapidly e x p a n d i n g geological map, t h e same t o o l — t h e same time m a c h i n e — used by William "Strata" S m i t h and t h e o t h e r geological founding fathers.

To tell t i m e Biostratigraphy begins in t h e field where t h e fossils are found. It ends in a museum of some sort, for only in a museum c a n o n e make the painstaking, comparative investigations t h a t enable o n e to identify fossils correctly. T h e discovery and definition of the units of geological time spanned t h e entire n i n e t e e n t h century. T h i s revolution in the understanding and c o u n t i n g of geological time was propelled by huge accumulations of fossils. All this newly collected material b e c a m e t h e bookkeeping of time, and as more fossil were collected, more and more types of fossils—types of species— poured into t h e various universities and geological surveys doing the collecting. All of this material h a d to go somewhere. T h e n i n e t e e n t h and early t w e n t i e t h centuries thus became a time of museum expansion. T h e great natural history museums, such as the A m e r i c a n Museum of N a t u r a l History, t h e Field M u s e u m in C h i c a g o , the S m i t h s o n i a n Museum in W a s h i n g t o n , D.C., and t h e British M u s e u m of Natural History, were created during the n i n e t e e n t h century. T h e y are dedicated to many things, but most of all they are storehouses of species. If o n e finds a fossil of u n c e r t a i n identity, sooner or later o n e must m a k e a pilgrimage to museums where representative 28

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specimens are housed. Natural history museums are o n e of t h e most important time machines of all. It is no c o i n c i d e n c e t h a t they grew into stately mansions during t h e periods of most active geological exploration of Europe and N o r t h America. Deciphering the age of rocks hy using fossils necessitates a clear understanding of just what constitutes a fossil "species." T h i s c a n be achieved only if large numbers of fossils h a v e been collected, organized, and c o m m i t t e d to a museum for later study. Eventually, any geologist w h o wants to understand ancient time using fossils ends up in a museum. In 1975 I found myself in such a place, a giant basement museum, a dark and dusty warehouse filled with metal cabinets holding corpses of a n c i e n t N o r t h A m e r i c a , t h e enormous fossil collection of t h e Geological Survey of C a n a d a . Outside, t h e cold wintet of O t t a w a held O n t a r i o in its frozen grip. Being from a warmer corner of N o r t h America, I had had no previous experience with such u n r e m i t t i n g winter. I had traveled here to see collections assembled by all my scientific predecessors, t h e long string of geologists w h o had traveled to t h e Vancouver Island region to collect fossils. T h e dates of these entries, ranging from a century ago to only a few years before, bore witness to long-standing curiosity. Atrayed in the boxes were specimens 1 had seen only in m o n o g r a p h s , fossils pristine and fragmentary, eloquent testimony to a proud geological survey's long work in deciphering t h e age of its northwest corner. I had come to see more t h a n fossils, t h o u g h . Five stories above me an old Russian worked away: George Jeletzky, o n e of t h e giants of geology a n d a world authority on Cretaceous a m m o n i t e s . Jeletzky was a legend for many reasons. He was prolific, he was a pioneer in Cretaceous geology, he was a refugee: He had fled t h e Soviet U n i o n during World War II, his fossils his only possessions, and made his way to C a n a d a . He still had a price on his head and faced execution if he ever returned to his n a t i v e Russia. W a r m , h u morous, and earthy, he was thus exiled forever for crimes imagined or political (if there is any difference). T h e t e may be no greater p u n i s h m e n t t h a n separating a Russian from his country. Jeletzky had spent years in t h e wilderness of western C a n a d a , deciphering the rock record of t h e C r e t a c e o u s there and splicing together the 29

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threads of insight afforded by t h e insular C a n a d i a n fossils with those from the rest of t h e world. Perhaps better t h a n a n y o n e on earth, he was capable, using fossils, of drawing the fine lines of time t h a t relate the various geographic regions of this far-flung earth. He had trekked over the entire region of Vancouver Island. Yet Sucia still remained an enigma. S o m e of its fossils were unique in t h e world, or so it seemed. It was still n o t certain h o w the shale of Sucia c o r r e l a t e d n o t only w i t h o t h e r C r e t a c e o u s - a g e d rocks in Europe b u t e v e n w i t h rocks in California a n d some regions of V a n c o u v e r Island. T h e best fossils for d e t e r m i n i n g ages for the latter parts of t h e Cretaceous are t h e curious, straight-shelled a m m o n i t e s called Baculites, forms found a b u n d a n t l y in t h e Vancouver Island region. A l t h o u g h t h e majority of a m m o n i t e s during their long, 360-million-year reign on earth were coiled like a nautilus shell, some, in t h e Cretaceous, tried t h e n e w tack of uncoiling their shells. T h e Baculites were o n e of t h e more extreme manifestations of this uncoiling. T h e i r shells were long tubes, a n d some became as large as a h u m a n . Most, however, were small. Nearly all of the Baculites showed two distinctive characteristics t h a t m a d e t h e m especially useful for dating rocks. First, they were extraordinarily a b u n d a n t . On Sucia there are easily ten times as many Baculites a m m o n i t e s as any o t h e r kind, and this is the pattern reported around t h e world. S e c o n d , for reasons still entirely u n k n o w n , the Baculites lineage showed very high rates of evolution and extinction. Each of their species lasted on e a r t h but a short time—often a million years or less. T h u s they are a m o n g t h e best of all time markers, tor their presence in sedimentary strata p i n p o i n t s very short intervals of time. T h e y can allow precise correlation between distinct rock assemblages. T h e western interior of t h e U n i t e d States has been subdivided into units of a half-million years or less, on t h e basis of the presence of Baculites species. N e w species of Baculites a m m o n i t e s appeared to h a v e b e e n forming in t h e vast western interior ocean at a prodigious rate between 90 and 65 million years ago, and t h a n k s to their amazing a b u n d a n c e , paleontologists for more t h a n a century had been able to use these fossils to subdivide the

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thousands of feet of shale in the western states. Such, however, was n o t the case for the west coast of N o r t h A m e r i c a . A l t h o u g h a very good Japanese paleontologist named Tatsuro M a t s u m o t o h a d recognized a handful of Baculites species from California in the mid 1950s, only two species h a d b e e n found in the Vancouver Island region, and o n e of these c a m e from Sucia Island. More disappointing yet was t h e discovery t h a t unlike t h e case in t h e western interior, where Baculites species appeared and disappeared with great a b a n d o n , the two Baculites from the Vancouver Island region just seemed to go on and on and never go extinct, lasting many millions of years. It made no sense to me. W h y would speciation of this type of a m m o n i t e be so abrupt in o n e place and so gradual in a n o t h e r ? My agenda in O t t a w a in t h a t cold winter was to look a n e w at the Baculites species k n o w n from t h e Vancouver Island region and c o m p a r e t h e m with others of the same group. O v e r m a n y days I lived in t h e dark basement, pulling from bulk collections t h e n u m e r o u s Baculites specimens collected over many years. W i t h h u n d r e d s of fossils to look at, it quickly b e c a m e clear that just as I had suspected while in t h e field on Vancouver Island, there were far more t h a n the two species t h a t Jeletzky had identified. I was electrified by this knowledge, for after nearly three years of work in this newfound paleontology, I had finally made a discovery t h a t would affect t h e u n d e r s t a n d i n g of geological time and its correlation from region to region. Species well k n o w n in California—but previously unreported from Vancouver island—were clearly present in rocks slightly younger and slightly older t h a n those in Sucia Island. W i t h this new information I could for the first time correlate the Sucia rocks with California, Alaska, and Japan. Perhaps five o t h e r people in the world would care. But those five would really care! T h e soldiers in the paleontological army are few, but they are dedicated. T h e next step was far more delicate, for I h a d to c o n v i n c e Jeletzky t h a t I was c o r r e c t — a n d t h a t he was wrong. It had b e e n he w h o had stated t h a t only two Baculites species were found in t h e Vancouver Island region. We met in his office (he was in his sixties t h e n ) , and he inspected my evidence. To my surprise he readily acquiesced to my changes in his findings. He

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laughed. "Let me tell you a secret," he said. "I never liked those Baculites fossils. T h e y all look alike to me. I never b o t h e r e d to really study t h e Vancouver Island species." A n o t h e r torch had been passed. Teacher and student, monk and acolyte; master and apprentice at t h e e n d of a long apprenticeship— two equals n o w reveled in o n e more fact beguiled from nature's grasp. Sucia became bracketed in time t h a t day. T h e long road traveled to arrive at t h e relative age of this particular group of rocks is typical n o t just of Cretaceous rocks but also of rocks and fossil from t h r o u g h o u t time. T h e scientists doing the studying and t h e times, rocks, and fossils they study always vary, but t h e methodology is remarkably similar. A n y study starts with o n e section of rocks and t h e n expands, eventually e n d i n g up in a museum. It is an example of n i n e t e e n t h - c e n t u r y scie n c e still working well on t h e threshold of t h e twenty-first century. T h e work of G a b b and others in N o r t h A m e r i c a showed t h a t crude but reliable worldwide correlation of fossil-bearing strata was possible. My work a century later was o n e of m a n y confirmations of t h e efficacy of this type of time m a c h i n e . Sedimentary rocks could be dated by studying their fossils. However, for most o t h e r rock types—such as igneous and metamorphic rocks—assigning any sort of age was impossible before t h e t w e n t i e t h century. T h e problem was t h a t fossils are found only in sedimentary rocks, never in igneous or most m e t a m o r p h i c types. Furthermore, even in sedimentary rocks fossils are only occasionally a b u n d a n t , and in many sedimentary rocks (such as glacier, river, and desert deposits) they are never present at all. Some m e t h o d o t h e r t h a n t h e use of fossils h a d to be developed for t h e purpose of dating rocks. Ultimately, several such systems were established. T h e most c o m m o n l y used of these newer systems, radiometric dating, is the subject of the n e x t chapter.

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W h e n a m m o n i t e s still lived and died a n d fell into t h e sandy b o t t o m o f what is now Sucia Island, N o r t h A m e r i c a was a divided c o n t i n e n t . For tens of millions of years during t h e Late C r e t a c e o u s Period, a giant seaway h u n dreds of miles wide cut t h e c o n t i n e n t in two. From t h e arctic regions of t h e far n o r t h to the Gulf of Mexico in t h e south, this wide yet shallow sea, called the Western Interior Seaway, was h o m e to an incredible bestiary of nowextinct creatures. A r c h a i c fish and giant m a r i n e reptiles prowled t h e blue waters in search of prey; monstrous turtles sculled a m o n g t h e wavetops; and giant clams were so a b u n d a n t t h a t their shells paved t h e muddy bottoms. Overhead, long-winged pterosaurs and primitive birds circled above t h e

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whitecaps, diving and sometimes fighting for surface-dwelling fish. A m monites lived and died in countless numbers in t h e sunlit portions of the sea, their empty shells littering t h e shallow sea b o t t o m s and sandy shorelines. To the west of this sea t h e Rocky M o u n t a i n s were rising, urged skyward by huge volumes of magma welling up a m o n g their roots. In places this magma pooled far underground, slowly solidifying to b e c o m e giant bastions of granite, t h e speckled foundation of any c o n t i n e n t . Elsewhere in the rising arc of m o u n t a i n s , t h e magma successfully fought to t h e surface, blasting outward from volcanic cones, creating smokestack pillars of blackness to t h e west of t h e inland sea. Falling ash from t h e volcanoes periodically covered the shorelines of t h e seaway, creating a rich, fertile soil. Riotous jungles grew and died in t h e swampy lowland areas along the margins of t h e great sea. Rivers large and small poured into the seaway, carrying to t h e central sea u n n u m b e r e d tons of sediment derived from the new m o u n t a i n s as they began to erode. Carried within or buried b e n e a t h this settling sediment were t h e remains of many creatures of t h a t time: the skeletons of fish, t h e shells of long-extinct mollusks. Yet t h e most valuable product for geological dating in this region c a m e n o t from t h e fossils but from the volcanic ash t h a t fell on this land. T h e intersection of this fine volcanic dust with sedimentary rock gives us a m e a n s of dating t h e fossiliferous sediments in terms of absolute years from t h e present, n o t merely relative position. T h e ash c a n be dated radiometrically. T h i s methodology is a m o n g the most scientifically useful ot time machines.

T h e age of t h e earth T h e r e has always b e e n a need to put absolute age d a t e s — t h e time, in thousands or millions of years ago, t h a t given rock formed—on t h e units of the geological time scale. Fossils alone c a n n o t do this. T h e y can help us sort out relative positions of strata but c a n n o t gives us their age in numbers of years ago. T h e solution to that problem awaited t h e discovery of radioactivity and t h e i n v e n t i o n of m a c h i n e s t h a t c a n measure t h e tiny quantities of chemicals called isotopes, t h a t are used to date a rock. T h o s e discoveries took place in

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the t w e n t i e t h century, but they were n o t spurred by t h e need to add absolute age dates to the geological time scale. Radiometric dating, t h e discipline of assigning dates to rocks, developed in response to an entirely different question: finding the age of t h e earth. By the late 1800s, t h e search for a reliable m e a n s of dating nonsedimentary rocks was a major goal of science. Economic motives were still important, just as they had been at t h e start of t h e century. But as t h e century came to a close, a more purely scientific reason for t h e better d a t i n g of rocks emerged. Scientists of t h e time became m u c h interested in d e t e r m i n i n g the age of the earth itself. T h e r e were many motives for this pursuit, but perhaps n o n e so pressing as those related to Darwin's newly proposed theory of evolution. T h i s theory necessitated an e a r t h of great antiquity, and b o t h Darwin's supporters and his detractors clamored for better information about t h e age of t h e earth. Discovering t h e age of t h e e a r t h was perhaps t h e most technically difficult challenge facing scientists of t h e late n i n e t e e n t h centuty. Two schools of thought prevailed. Most geologists, recognizing t h e immense thickness of sedimentary rocks scattered over t h e globe, believed t h a t billions of years had transpired since the origin of t h e earth. T h e great diversity of fossils encased in all these strata seemed to support this view, because Darwin's theory of organic evolution required t h a t great expanses of time must h a v e elapsed since the origin of the earth to allow fot t h e e v o l u t i o n of organisms n o w present in such great diversity. By contrast, physicists t h o u g h t t h e e a r t h was m u c h younger t h a n this, perhaps a few h u n d r e d s of millions of years old. T h e s e clashes, the first to pit against each o t h e r t h e physical scientists and those who styled themselves "naturalists," were a harbinger of t h e future, and they were immensely bitter. At this time, t h e m a n most n o t a b l e for addressing t h e question of t h e age of the earth was William T h o m s o n , better k n o w n by t h e title of his peerage: Baron Kelvin of Largs Ayrshire—Lord Kelvin for short. T h o m s o n has been described as the most h o n o r e d British scientist in history, and he was certainly the most famous scientist in t h e wotld at t h e end of t h e n i n e t e e n t h century. He was elected president of t h e Royal Society and was re-elected 35

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five times. During his illustrious career, T h o m s o n , or Kelvin, published over 600 scientific articles and books. It was he w h o , t h r o u g h brilliant insight and m a t h e m a t i c a l calculation, made t h e first scientific c o m p u t a t i o n of the age of the earth. Kelvin's results seemingly struck a mortal blow to Charles Darwin's theory of evolution, for Kelvin's e s t i m a t e — t h a t the earth was created less t h a n 100 million years ago—did n o t seem to allow e n o u g h time for the myriad creatures found on earth to h a v e evolved. Kelvin's estimate was based on his scientific passion: the study of heat and h e a t flow (the absolute temperature scale bears his n a m e ) . It was k n o w n at t h a t time t h a t each transformation of energy from o n e form to a n o t h e r results in t h e formation of heat, w h i c h is t h e n dissipated. This fact, which eventually become k n o w n as the second law of thermodynamics, is the reason why perpetual m o t i o n m a c h i n e s are impossible—energy is always lost by any mac h i n e , and in every transfer of energy. Kelvin reasoned that the earth and the sun are b o t h cooling and that, by establishing the initial temperatures of each of these bodies, as well as their rate of h e a t loss, he could arrive at an estimate of their age. Measuring t h e rate of t h e sun's h e a t loss was difficult, but measuring t h a t loss for t h e earth was n o t . Kelvin needed just three values: the initial temperate of t h e earth, t h e thermal conductivity of rocks, and the actual heat flow. He used a value of 3 8 7 0 ° C as the initial temperature of the earth, because this was t h o u g h t to be a reasonable estimate of the temperature at which rocks melt to a m o l t e n state, and because he assumed that the earth formed from an originally hot, magmatic body (rather t h a n coalescing from many cold fragments). H e a t flow measurements for various types of rocks were obtained in t h e laboratory. All t h a t was wanting was a measure of the actual rate at w h i c h h e a t was escaping from t h e earth's interior, and this was found by measuring t h e earth's temperature at various depths in underground mines. N o t only did these experiments indicate t h a t heat is indeed flowing outward from t h e deep interior of t h e earth but the initial rate they suggested was so high that it implied a relatively young age for the earth. Kelvin's calculations were considered highly authoritative, n o t so m u c h for how they were d o n e but because of w h o Lord Kelvin was. Kelvin's conclusion about a relatively young earth was soon supported by others w h o studied 36


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heat flow, most notably by C l a r e n c e King, director of t h e Geological Survey of C a n a d a . King, using Kelvin's methodology, arrived at an e v e n lower estimate t h a n Kelvin's; he calculated that the earth was only 24 million years old. T h e K e l v i n - K i n g conclusions regarding t h e age of t h e e a r t h were widely but n o t universally accepted. T h e chief dissenters were those familiar with evolution and t h e fossil record—such as Darwin's "bulldog," T h o m a s H u x l e y — a n d those w h o studied the rate at w h i c h sedimentary rocks accumulate. Twenty-four million years was far too short a time to a c c o m m o d a t e all of t h e evolutionary changes visible in t h e fossil record, and it was also too short to account for the a m o u n t of sedimentary rock present on the earth's surface. W i t h regard to t h e latter, in 1895 t h e geologist William Sollas estimated t h a t thickness to be more t h a n 100,000 meters, if it were to be piled upward in one c o n t i n u o u s c o l u m n . A c o l u m n of sediment 60 miles tall, sitting on the surface of the earth, would certainly take time to form, assuming that the processes (and rates) of sedimentary rock a c c u m u l a t i o n h a v e b e e n uniform through time. Sollas t h e n asked t h e following question: W h a t is the rate at which sedimentary rocks, past and present, can be expected to accumulate? He assumed t h a t sedimentary rocks a c c u m u l a t e at a rate of about 1 meter each 300 years and thus arrived at an estimate of about 34 million years for the age of t h e earth since s e d i m e n t a t i o n began. T h i s figure was very much a minimum, for it assumed t h a t t h e sedimentary rocks accumulated without pause or break. In fact, however, most sedimentary rocks accumulate in sporadic fashion, and t h e r e may be long periods of t i m e w h e n no sediments accumulate. Furthermore, t h e Sollas estimate did n o t a c c o u n t for the long stretch of time t h a t passed, because of t h e eatth's eatly, m o l t e n surface, before sedimentation e v e n began. A mote ingenious a t t e m p t to arrive at a reliable estimate of earth's age came to be k n o w n as t h e "salt clock." T h e a m o u n t of salt in t h e ocean, and the tate at which it arrived there, were t h o u g h t to offer a way of calculating the age of the earth. Using this m e t h o d , several chemists arrived at an estimate of about 100 million years. By t h e eatliest part of t h e t w e n t i e t h century, physicists, chemists, and geologists had reached consensus on a figure of between 25 and 100 million 57

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years for t h e age of t h e earth. O n l y the evolutionists found this n u m b e r implausible, for they believed t h a t t h e workings of organic evolution required m u c h longer stretches of time to generate all the organic diversity found on earth today. As we k n o w now, their misgivings were well founded. T h e ttue age of t h e e a r t h is measured in billions of years, n o t millions. T h i s discovery came about as a by-product of d e v e l o p m e n t s in t h e field of nuclear physics, which eventually gave us a means of dating volcanic ash. N e a r t h e close of t h e n i n e t e e n t h century, at t h e peak of Kelvin's emin e n c e , t h e seeds of his downfall—in terms of his estimate of the earth's a g e — h a d just b e e n sown. In 1895 W i l h e m R o e n t g e n of G e r m a n discovered X-rays, and a year later A. Becquerel of France discovered the radioactive properties of uranium. Two years after that, Marie Curie discovered similar properties for t h e e l e m e n t thorium and coined the word radioactivity.

Radioactive decay T h e b r e a k t h r o u g h leading from t h e first discovery of X-rays and radioactive elements to accurate age d e t e r m i n a t i o n in geology came from Ernest Rutherford and Frederick Soddy of M c G i l l University in M o n t r e a l , w h o discovered the principle of radioactive decay and "half-life." In radioactive decay, an atomic nucleus undergoes transformation i n t o o n e or more different nuclei, the original e l e m e n t often b e c o m i n g in t h e process a different e l e m e n t . By 1907 Rutherford made t h e first suggestion t h a t radioactive decay processes could be used as a geological timekeeper: If t h e rate of production of helium from k n o w n weights of the different radio-elements were experimentally k n o w n , it would thus be possible to d e t e r m i n e t h e interval required for t h e production of t h e a m o u n t of h e l i u m observed in radioactive minerals, or, in o t h e r words, to d e t e r m i n e t h e age of t h e mineral. T h e s e p r o p h e t i c words heralded a new era of age d e t e r m i n a t i o n . Rutherford quickly calculated t h e age of two minerals, finding minimal ages

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of 500 million years for each—far older t h a n t h e greatest age of the earth itself as calculated by Kelvin and others. S o o n o t h e r wotkers began analyzing rocks t h a t c o n t a i n e d radioactive elements. By 1907 a slightly improved m e t h o d yielded a series of ages all m u c h greater t h a n t h e 100 million years proposed by Kelvin as t h e maximal age of t h e earth. T h e greatest of these was 2.2 billion years. T h e discovery of radioactivity—and t h e natural clock with which it keeps t i m e — m a d e Kelvin's simple c o n d u c t i v e calculation obsolete. Kelvin's mistake was to assume t h a t no n e w h e a t had b e e n created in the earth since its origin. Radioactive decay produces such "new" heat. T h e new m e t h o d of age dating, based on radioactive decay, required accurate measurement of the isotopic ratios of various elements. T h e isotopes of an element are atoms of that element that have the same number of protons but different numbers of neutrons. Perhaps the best-known example is carbon-14, which is found in very small quantities compared to its far more c o m m o n sister isotope, carbon-12 (the numbers refer to the atomic weight of the a t o m ) . T h e transformation of one isotope into a n o t h e r that we call radioactive decay takes place at a k n o w n and constant rate. T h e r e are 339 isotopes of 84 elements known in nature; 269 of these are stable (they do n o t change), and 70 are radioactive. Of the 70 radioactive isotopes 18 are too "long-lived" to be useful; they have too long a half-life (the a m o u n t of time required for exactly half of the parent isotope to be transformed into the daughter isotopes). T h e early geochronologists e x a m i n e d only t h e breakdown of uranium into lead for age dating. Today o t h e r isotopic pairs are e x a m i n e d , t h e most useful being potassium/argon and argon/argon. T h e potassium/argon ( K / A r ) method measures the telative a m o u n t s of potassium-40 and successor argon40. T h i s m e t h o d is the most widely used of all radiometric dating m e t h o d ologies

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promised by c o n t a m i n a t i o n . Because argon is an inert gas, it n e v e r combines chemically with any o t h e r material in t h e rock, and it escapes as a gas w h e n a rock is heated. Potassium is o n e of t h e most a b u n d a n t e l e m e n t s in rocks and is constantly breaking d o w n into argon, w h i c h t h e n escapes in most cases. However, under special circumstances t h e potassium/argon "clock" is

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set in m o t i o n in such a way t h a t geologists always know that they are dating the true formation of a given rock: T h e s e special conditions occur w h e n m o l t e n magma cools and solidifies. A n y lava has a great deal of potassium, and t h e argon heing produced by radioactive decay is n o t trapped because of the h e a t and liquidity of t h e lava. W h e n t h e lava cools, however, crystals of feldspar and o t h e r minerals form, each c o n t a i n i n g potassium-40 that is decaying to argon-40 at a rate such t h a t half of t h e potassium will be transformed into argon in 1.25 billion years. T h e m o m e n t the crystal forms, the clock is set at 0. Recently, t h e K/Ar m e t h o d has been improved. Samples with potassium crystals are irradiated with fast n e u t r o n s in an atomic reactor, which converts a fraction of potassium-39 to argon-39. T h e ratio of t h e two argons is t h e n e x a m i n e d . T h i s t e c h n i q u e is t h e most precise of all dating methods, but it can be used only on rocks a million years of age or older. In younger rocks t h e r e just has n o t b e e n e n o u g h time to cause measurable accumulations of t h e d a u g h t e r isotopes. By t h e earliest part of t h e t w e n t i e t h century, m u c h of t h e theory beh i n d radiometric age dating h a d b e e n worked out. W h a t was necessary to apply t h e theory, however, was a reliable set of instruments. T h e physicists needed to measure tiny quantifies of specific isotopes with great precision. It was n o w up to t h e instrumentalists to put theory into practice. T h e m a c h i n e necessary to measure various isotopic quantities is k n o w n as a mass spectrograph. T h e first of these elegant m a c h i n e s was designed by t h e physicist J. J. T h o m p s o n of t h e C a v e n d i s h labs in Cambridge, England. His crude prototype was soon redesigned by a colleague in t h e same lab, F. W. A n s t o n , w h o n a m e d his creation t h e "positive ray spectrograph." W i t h this m a c h i n e , A s t o n began measuring t h e isotopic compositions of many materials. In 1927 he turned his a t t e n t i o n to t h e radioactive decay of lead isotopes, and in so doing l a u n c h e d t h e field of research t h a t eventually gave us some of t h e most profound insights into n o t only the age, but also t h e form a t i o n , of t h e solar system. Mass spectroscopes h a v e speciated and multiplied over t h e years, and now they are quite task-specific. T h e y are a m o n g the most c o m m o n of major 40


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laboratory instruments; thousands are operated daily t h r o u g h o u t the world. Some investigators c o n t i n u e to look at t h e relative isotopic composition of earth material to produce reliable dates. O t h e r s e x a m i n e lighter isotopes of carbon and oxygen in order to measure a n c i e n t temperatures. M a n y scientists, however, are still dedicated to finding t h e age of rocks and to solving the most interesting question of all: H o w old is t h e earth? T h e most recent measurements suggest an age of at least 4.5 billion years.

Returning to rocks Ironically, t h e techniques of radiometric age d a t i n g work best on those rocks that most stubbornly resisted n i n e t e e n t h - c e n t u r y efforts to d e t e r m i n e ages— the igneous rocks, which never c o n t a i n fossils. Radiometric dating m e t h o d s work least well on those rocks t h a t c o n t a i n fossils. T h e most sophisticated mass spectroscope in t h e world is useless on an ordinary fossil-bearing sedimentary rock. If a sedimentary rock is to be dated radiometrically, there must be some type of interbedded lava flow or ash layer locked within. Unfortunately, such events were relatively rare. Just as clearly, t h e majority of sedimentary rocks c a n n o t be directly dated. T h e only solution was to find a way to date rocks in those places where sedimentary rock units and volcanic rock units intersected in t i m e — places where ashes or lava flows c a n be found interbedded with a n c i e n t sedimentary rocks. Such places became the new holy grail t h a t geologists sought. Paleontologists and o t h e r geologists learned a new word and learned to recognize a new rock type: b e n t o n i t e , a t h i n orange layer of lithified volcanic ash found in sedimentary rock. Arriving at age dates for C r e t a c e o u s sedimentary rock has b e e n a particularly vexing problem. T h e original type areas exposed in Europe were deposited in tegions far from active volcanoes so they h a v e few or no bentonites. M u c h better beds are found in t h e western interior of N o r t h America, east of t h e Rocky M o u n t a i n s — t h e site of t h e a n c i e n t Western Interior Seaway. 41

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T h e microscopic ash particles erupted out of t h e a n c i e n t Rocky M o u n tains during t h e C r e t a c e o u s Period are t h e source of our hest age dates for t h e Age of Dinosaurs. W h e n these microscopic crystals first hit t h e air, they cooled, w h i c h allowed tiny feldspar crystals rich in potassium to form. Most of these ash particles hit t h e surface of a wide inland sea east of t h e volcanoes, t h e seaway t h a t bisected t h e N o r t h A m e r i c a n c o n t i n e n t between 100 million and about 70 million years ago. T h e ash t h a t fell on t h e land was quickly washed away by rain and destroyed. But, e a c h m o n u m e n t a l volcanic hurst also sent a shower of ash o n t o t h e seaway's hroad surface, where it slowly sank, finally to c o m e to rest on deep, murky sea b o t t o m s where fish and shells—and above all a m m o n i t e cephalopods—lived and died in numbers beyond counting. Inside each of t h e tiny crystals of feldspar forming this s u n k e n ash, isotopes decayed from o n e to a n o t h e r like, well, clockwork. T h e thick shale, sandstone, and ash deposits of t h e Western Interior Seaway can be seen t h r o u g h o u t t h e central part of N o r t h America. In Colorado, W y o m i n g , t h e Dakotas, Arizona, Alberta, Manitoba, M o n t a n a , N e braska, and Kansas, t h e s e d i m e n t a t i o n of more t h a n 50 million years is visible. Better t h a n any o t h e r place on earth, this stack of sediment contains markers, b o t h fossil and igneous, that can be used to tell time, Cretaceous time. T h e fossils alone m a k e t h e region extraordinary. T h e best-preserved a m m o n i t e s in t h e world c o m e from hete—beautiful pearly shells from t h e Pierre S h a l e and its C a n a d i a n equivalents. So gorgeous are these fossils that a n e w mineral industry has sprung up, producing a reddish jewel called ammolite. Yet it is n o t t h e extraordinary completeness and pristine nature of t h e fossils t h a t makes t h e m so useful to t h e geologist ( t h o u g h all of that helps); rather it is their very a b u n d a n c e , and the rapid d a n c e of e v o l u t i o n they

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to h a v e engaged in. T h e W e s t e r n Interior Seaway was a cauldron of evolutionary c h a n g e . All m a n n e r of creatures evolved rapidly in this n u t r i e n t - r i c h inland sea. A m m o n i t e s seem h a v e b e e n especially b i t t e n by this itch to evolve, which accelerated t h e creation of new species. Most speciation is aided and abetted by geographic separation; some small band is split off from t h e larger popula42


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tion centers and, t h r o u g h time and isolation, gradually (or rapidly) is transformed into a new species, a form no longer capable of successfully reproducing with members of t h e old group. N e w species are generally characterized by new morphologies, a n d so it was with t h e a m m o n i t e s , w h i c h changed their shells rapidly by adding or subtracting ribs, by altering t h e spines, and by twisting or unrolling or t i g h t e n i n g t h e loops t h a t defined their shells' shapes. T h e great breakthroughs t h a t enabled scientists to use radiometric dating for sedimentary rocks with enclosed ash beds are n o t limited to C r e t a ceous rocks. Radiometric dating has n o w b e e n applied to sedimentary rocks of all ages and has made it possible to assign numerical ages to t h e entire geological time scale. T h e r e are still many uncertainties. But progress has b e e n rapid and the scientific benefits enormous. We can use this information in the search for oil and minerals and to answer questions about rates of evolution. T h e use of this time m a c h i n e has been a major milestone in t h e study of the past. For work with Cretaceous-aged rocks, the benefits h a v e b e e n enormous. Here, finally, was t h e realization of D'Orbigny's dream: time, as elucidated by an u n b r o k e n sequence of sedimentary rocks sprinkled with fossils and diagnostic ash beds. By interleaving information from t h e two, geologists put together the highest-resolution scheme of ages found for any of the earth's geological time scale units. Because many of t h e W e s t e r n Interior ammonites could be found in Texas and e v e n Europe, this time scheme allowed direct correlation with these faraway places. T h e standard for time, Cretaceous time, became centered in t h e middle of N o r t h America. Yet o n e great problem remained: N o n e of these fossils could be found further west, along the Pacific coast of N o r t h A m e r i c a , in Japan, or elsewhere in t h e vast Pacific O c e a n region. To tell the time of these places, including a n c i e n t Sucia Island, required an additional s t e p — t h e i n v e n t i o n of an entirely new type of geochronometry device. T h e age of t h e Cretaceous on t h e western margins of the N o r t h A m e r i c a n c o n t i n e n t was decoded by using t h e earth's magnetic field.

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The malevolent California sun stabbed t h r o u g h swarms of insects t h a t late afternoon in t h e typically h o t summer of 1980, its fangs gradually releasing their grip on day. My new graduate student Jim Haggatt and I sat in a cool pool, watching amphibious insects bobbing merrily in t h e rushing creek, and trying n o t to notice t h e cheerful skinny dippers several h u n d r e d yards downstream. As we lazed, resting stretched muscles, our ears still rang from a day spent drilling and coring Cretaceous-aged rocks. We were distant from any town, far up a c a n y o n carved deeply into t h e Sierra N e v a d a , trespassing like the locals on private land held in trust by a California h u n t i n g c l u b — l a n d purchased so t h a t its absentee landlords could slaughter t h e local deer in

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privacy. We rationalized our illegal trespass on t h e principle t h a t science was more important t h a n land rights, but in t r u t h t h e h u n t e r s probably didn't care. T h e y rarely visited their land this time of year and in any case were far less likely to resent our activities t h a n those of t h e local pot farmers w h o managed t h e land farther upstream. All around me I could see t h e results of our labors: On t h e edge of t h e creek were piles of white bags, each containing a tubular rock core about 2 inches long and an inch in diameter. In the b a n k I could see t h e scars t h a t yielded up these cores, small holes bored into the solid rock by our gasoline-powered drills modified from c h a i n saws. Also on t h e creekside lay: c l o t h sample bags filled with pearly fossils: beautiful coiled a m m o n i t e s and flat w h i t e n e d clams wrested by h a m m e r blow from the e n t o m b i n g sediment t h a t makes up t h e creek b o t t o m and its canyons. It had been 12 hours since we h a d climbed out of sleeping bags. I suppose I was tired, but h o w tired could you be at 30 years old, w h e n you believe you are on t h e verge of putting an accurate age on sediments k n o w n to scientists for over a century? H o w tired can you be sitting naked in a cool creek with n o t h ing left to do t h a t day except scrounge up dinner? We had taken samples that would tie us into a web of research t h a t originated with the classic work done in France and I t a l y — t h e tegions first studied by t h e pioneering geologists a century or more before us.

T h e geomagnetic polarity time scale T h e two most c o m m o n m e t h o d s for distinguishing units of geological time are using fossils ( w h i c h yields only a relative age) and measuring t h e radioactive decay of o n e isotope i n t o another, w h i c h yields an age in years. Yet if you reside in a land where t h e fossils are unique and new, or where n o n e of the rocks c o n t a i n t h e elusive minerals t h a t embody radiometric clocks, you h a v e no way to tell your rocks' age. Luckily for those interested in t h e age of rocks from t h e west coast of N o r t h A m e r i c a , however, there are o t h e r m e t h ods as well. O n e of t h e most powerful yet least expected timekeepers emanates from t h e earth's magnetic field. In California, in t h e early 1980s, I was the first to use paleomagnetism (as this dating system is called) to arrive at 46

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an age for t h e Cretaceous of California, and in so doing I took t h e first major step toward finding t h e age of Sucia Island. T h i s tool had b e e n widely used for other time periods and o t h e r places, but never before in western N o r t h America. All magnets exhibit the curious property of being bipolar; they all h a v e positive and negative poles. In an e x p e r i m e n t beloved of sixth-grade science teachers, iron filings sprinkled around a magnet obediently orient themselves in c o n c e n t r i c patterns a r o u n d these poles. Less obvious, however, is t h a t the poles are producing forces t h a t differ markedly in direction. W h y does a compass needle always seek t h e N o r t h Pole rather t h a n simply p o i n t i n g toward either the n o r t h or the south pole? A compass, after all, is n o t h i n g more t h a n a small magnet in a closed box, a m a g n e t whose positive pole always seeks the direction of a negative m a g n e t i c pole. W h e n placed together, two magnets either cling to or repel e a c h other, d e p e n d i n g on w h e t h e r their positive and negative poles are in c o n t a c t . A l t h o u g h t h e forces e m a n a t i n g from these poles are of equal intensity, s o m e t h i n g about t h e m is markedly different. T h e magnets with w h i c h everyone is familiar, be they horseshoeshaped, rods, or the small disks placed on refrigerators, are all quite consistent in theit polarity: T h e i r positive a n d negative poles are always in the same place. But other, more complicated magnets can be m a d e to act in a more variable m a n n e r : T h e i r polarities sometimes c a n be traded, so t h a t the positive pole becomes negative and t h e negative pole positive. Magnets come in all sizes. T h e largest we are acquainted with ( t h o u g h there may be many larger out in space) is t h e earth. T h e e a r t h acts as t h o u g h it had a huge bar magnet in its interior, aligned roughly n o r t h - s o u t h . At first glance, the earth would seem to be an unlikely magnet: W h y does it h a v e magnetic properties at all? Perhaps metal on the earth's surface creates the earth's magnetic field. But closer scrutiny casts doubt on this possibility. Most of the eatth's crust is made up of nonmetallic matetial, and thus n o n magnetic material. T h e t e clearly isn't e n o u g h metal to produce t h e enormous magnetic field surrounding t h e earth, a field so strong t h a t it can deflect cosmic rays and solar radiation t h a t would otherwise strike our planet's 47

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surface. It turns out t h a t this magnetic field e m a n a t e s from deep within. Its source is the innermost shell of t h e earth, a liquid iron core, which hehaves like a magnetic d y n a m o . Even t h o u g h t h e magnetic field of the earth (like all magnets) has two distinct poles, it can be t h o u g h t of as being cteated by a uniformly magnetized sphere. T h e magnetic field pole p o s i t i o n s — t o d a y — a r e 79N, 7 0 W and 79S, 110E. Yet these positions are n o t fixed on t h e earth. It has long been k n o w n t h a t t h e positions of t h e m a g n e t i c poles c h a n g e . T h e magnetic field can be described by t h r e e variables: its intensity, or strength at any geographic position; its declination, w h i c h is t h e deviation of the n o r t h magnetic pole from t h e geographic n o r t h pole of t h e earth's rotational axis; and its inclination, or t h e steepness of t h e field at any geographic point (If a compass needle is allowed to m o v e freely, it will dip downward, seeking the magnetic pole. T h e angle of this downward dip is t h e i n c l i n a t i o n ) . Of these three, declination shows t h e most m o v e m e n t . T h e declination of L o n d o n was 11E in 1580 and was 2 4 W in 1 8 1 9 — a c h a n g e of more t h a n 36 degrees in 240 years. T h e r e are only two ways to account fot this change. Either L o n d o n moved or t h e magnetic pole wanders across the face of t h e earth t h r o u g h time. T h i s m o v e m e n t is called secular m o v e m e n t . T h e secular m o v e m e n t of t h e magnetic poles was a key discovery of the n i n e t e e n t h century. But an e v e n more startling discovery was made in the early t w e n t i e t h century: T h e poles c a n reverse polarity. In the early 1900s, two French geologists, using t h e most primitive e q u i p m e n t , discovered that the same lava outcrops in France preserved two diametrically opposing directions of polarity. Because t h e polarity was detected from rocks long since solidified, these earliest paleomagnetic measurements were looking at fossil compasses, where t h e directions of t h e magnetic poles could be determined. T h e fact t h a t two opposing directions were found in t h e same masses of lava sparked debate t h a t c o n t i n u e d for decades. Finally, after repeated measurements with ever-more-sophisticated e q u i p m e n t , there was but o n e inescapable conclusion: T h e eatth's magnetic field had somehow switched polarity, t h e positive pole b e c o m i n g negative, and vice versa. T h e only alternative e x p l a n a t i o n was t h a t t h e whole earth itself h a d rotated 180 de4^

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grees so that t h e n o r t h pole b e c a m e t h e south pole. T h e rotation and orientation of the earth had n o t changed. T h e direction of t h e earth's magnetic field had! W h y reversals occur is a mystery. Many theories a b o u n d , and all deal with complex interactions taking place deep within t h e earth. T h e earth's

A) Orientation of Earth's magnetic field with the internal dipole coincident with spin axis. B) Magnetic pole position during the last several hundred thousand years. C) position of modern north magnetic pole.

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c o r e — t h e innermost of t h e three largest shells of earth structure—has never been observed and never can be, Jules Verne fantasies aside. Yet we know a great deal about it, and m u c h of this information comes from the way and the rate at which earthquake waves more through the earth. T h e core, unlike the overlying mantle, is liquid, but liquid in a hellish way. It is under such high pressure t h a t although we technically classify it as a liquid, it is a type of liquid t h a t c a n n o t exist on t h e surface. T h e composition of the core is metallic (it is composed of iron and nickel), and its c o n t a c t with overlying mantle (which is "solid") must be o n e of the more interesting places in the solar system. C o m p l e x interactions t h a t occur at this c o r e - m a n t l e interface have enormous ramifications for the rest of the planet. T h e discovery that the core is made of hot liquid metal showed t h a t it is the source of the magnetic field, and the perturbations, eddies, c o n v e c t i o n currents, or other types of movem e n t within t h e spinning core may account for the magnetic reversals. Perhaps irregularities or gigantic phase interactions between this liquid core and the overlying, solid m a n t l e region somehow trigger the phase changes. Because these regions are located thousands of miles b e n e a t h our feet, the evid e n c e on h o w and why a polarity reversal takes place is never direct. Scientists h a v e long k n o w n about reversals. It was not until the 1960s, however, t h a t t h e implications of this discovery for calibrating geological time became apparent. It was t h e n t h a t geologists began sampling thick piles of lava flows on t h e edges of volcanoes. Because e a c h individual lava flow could be accurately dated using potassium/argon techniques, scientists were able to record a relatively precise series of ages for t h e flows. Each dated flow was t h e n sampled for its paleomagnetic direction. To t h e surprise of the investigators, n o t only could individual normal and individual reversed directions be detected, but many of these reversals in magnetic field were observable. Geologists soon realized t h a t t h e present, " n o r m a l " magnetic field direction has existed only for about t h e last half-million years. Prior to t h a t , t h e field was "reversed" relative to its present pole directions. As ever-older piles of lava were sampled, it b e c a m e clear t h a t the interval between reversal episodes was irregular but generally quite l o n g — o n the order of h u n d r e d s of thousands to millions of years. SO

A) Formation of magnetic anomalies in deep sea crust as produced at mid-ocean ridge spreading center. R) Radiometric dates and reversal history for the last 4-5 million years. 51

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At about t h e same time, oceanographers made a similar discovery for underwatet volcanoes. In t h e eatly 1960s, plate t e c t o n i c theory proposed that new oceanic crust ( w h i c h is composed of lava) is created by long, linear volcanoes arranged along submarine m o u n t a i n chains called spreading centers. N e w o c e a n crust is t h e n carried away from this spteading center, carried piggyback on a thicker layer of t h e earth's crust. W h e n oceanographers towed, over t h e spreading centers, instruments capable of detecting the orie n t a t i o n of t h e eatth's magnetic field, they observed regions of normal and regions of reversed polarity symmetrically arrayed around t h e spreading centers. T h e m a g n e t i c signals looked like great striped patterns, which were ultimately mapped across all of t h e earth's o c e a n bottoms. T h e only thing investigators needed to obtain a chronology of t h e reversal history of the earth's magnetic field was an age m e a s u r e m e n t for each stripe. T h e s e measurements were soon obtained by a ship specially designed to sample lava and sediment cores drilled from t h e b o t t o m of t h e sea. By t h e late 1960s, these cores h a d provided e n o u g h information about age a n d polarity for a "polarity t i m e scale" to be constructed. T h e greatest a d v a n t a g e of using m a g n e t i c reversals as t i m e indicators is t h a t they are worldwide, or " i s o c h r o n o u s , " t i m e surfaces. By themselves they are virtually useless; t h e r e h a v e b e e n so m a n y reversals during e a r t h history t h a t no individual reversal is identifiable. However, c o m b i n e d with o t h e t d a t i n g t e c h n i q u e s , such as biostratigraphy (telling t i m e with fossils) and radiometric d a t i n g , t h e p a t t e r n of m a g n e t i c field reversals becomes a very powerful tool. E a c h t i m e a field reversal takes place, it leaves its indelible signature in t h e earth's history and provides a worldwide time marker of e n o r m o u s utility. T h e record of reversal t h r o u g h t i m e is n o w well k n o w n . T h a t a c c u m u l a t e d record is called t h e g e o m a g n e t i c polarity time Scale, or GPTS. Detecting t h e record of these geomagnetic reversals is theoretically simple, but like m a n y theoretically simple things, t h e actual d e t e c t i o n process is often less so. T h e e v i d e n c e comes from the directions of untold n u m b e t s of tiny, magnetized mineral particles locked within either sediment or lava.

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T h e most c o m m o n of these magnetic minerals, m a g n e t i t e , is a rod-shaped crystal with a positive and a negative pole, just like any o t h e r magnet. S o m e of these mineral grains are microscopic in size, and if they exist in a medium where they can move freely (such as in watet or e v e n in unsolidified lava), they act as tiny compass needles. T h e i r positive pole will point toward the negative pole of t h e earth's great magnet. If present in sufficient quantity, they endow their enclosing m o t h e r rock w i t h a magnetic signal. Magnetic particles yield useful information about a n c i e n t magnetic fields in volcanic and in some sedimentary rocks. B o t h of these rock types preserve an actual record of t h e earth's m a g n e t i c field direction in m u c h t h e same way. W h e n h o t magma cools and solidifies, t h e m a g n e t i t e crystals found within t h e cooling lava b e c o m e aligned to t h e present field direction. A similat thing h a p p e n s w h e n sediments lithify from a wet slurry to solid rock and, in t h e process, lock in place t h e tiny m a g n e t i c minerals, all aligned in o n e direction hy t h e earth's m a g n e t i c field at t h e t i m e of the rock's fotmation. These two types of rock n o w c o n t a i n weak—but measurable—magnetic signals. // the exact orientation of the rock is known, t h e n a piece of t h e rock, carefully removed and t a k e n to t h e lab, c a n yield n o t only its m a g n e t i c intensities but also the actual direction of t h e earth's m a g n e t i c field w h e n the rock was formed. T h u s o n e can learn w h e t h e r t h e rock in question was lithified during a period w h e n t h e n o r t h pole of t h e e a r t h coincided with t h e positive pole of the earth's magnet, or vice versa. T h e pioneering geophysicists, w h e n measuring closely spaced samples from piles of lava, found t h a t there was a r a n d o m p a t t e r n of reversals. S o m e times thick piles of lava recorded n u m e r o u s reversals; and sometimes an equal thickness—and, perhaps, an equal t i m e period—recorded no reversals at all. T h e reversal themselves had no identity. Like a computer, they simply record binary data. But just as a simple plus-and-minus c o m p u t e t code c a n teveal, retain, or record great quantifies of infotmation w h e n e n o u g h data are accumulated, so too can our rich record of magnetic reversals tell us much about time.

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S y n c h r o n i z i n g our w a t c h e s An enormous a m o u n t of new understanding about the history of the oceans came from study of t h e deep sea cores collected by the O c e a n Drilling Program. We learned t h a t t h e ocean basins are young compared to c o n t i n e n t s and t h a t they are e p h e m e r a l . Yet a l t h o u g h we greatly improved our understanding of t h e history of o c e a n basins, t h e d e e p sea cores did little to improve our understanding of polarity changes, because t h e soft muck brought up by t h e drill cores disintegrated easily and so yielded little information about a n c i e n t magnetic directions. It was thus virtually impossible to correlate b e t w e e n t h e reversal records found in this undersea lava samples (with their isotopic ages) and t h e biostratigraphic time scale made up of landbased fossil occurrences. C o r r e l a t i o n b e t w e e n t h e deep sea samples (with radiometric and magnetic information) and t h e European stratotype sections (with fossil information) was thus problematic at best. T h i s problem was especially p r o n o u n c e d for t h e Cretaceous. Nearly all stages originally defined by d'Orbigny and his followers were identified in shallow-water limestone, which, it turned out, was without any magnetic minerals or e v e n ash beds appropriate for radiometric dating. Even more troubling, t h e various outcrops were discontinuous; they were isolated in various villages or seacoasts and could n o t be assembled into any sort of composite sequence or pile. W h a t was needed was a readily accessible record of hard, magnetically measurable strata in Europe c o n t a i n i n g b o t h fossils and a paleomagnetic signal. If a thick sequence of fossiliferous strata could be found with a record of t h e magnetic reversal history, t h e reversals could be used to d e t e r m i n e t h e age of t h e strata. S u c h a record was discovered in the early 1970s, in the A p e n n i n e M o u n t a i n s of Italy. T h e discovery of the best region for calibrating reversals and the geological time scale as defined by fossils came about by accident. In his recently published book T rex and the Crater of Doom, geologist Walter Alvarez noted that he and co-worker Bill Lowrie undertook the Herculean labor of sampling thousands of oriented cores from thick sedimentary successions of white lime-

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stone in central Italy because they were looking for evidence t h a t t h e Italian peninsula had "rotated" in the geological past during tectonic intetactions with Western Europe. Laboratory analyses of these cores, however, showed that there was so m u c h m o v e m e n t of various limestone layers, o n e upon another, that no detailed history of plate m o t i o n could be obtained. W h a t did emerge was an unexpected and magnificent record of magnetic reversals. Because these Italian limestones contained a rich record of microfossib (mainly the skeletons of single-celled organisms called planktonic fotaminiferans), the individual reversals discovered by Lowrie and Alvarez could be correlated both with other land-based sections and with deep sea lava, where reversal boundaries were dated using radiometric techniques. Fot t h e first time, European fossils could be associated with radiometric dates by using t h e magnetic reversal history as a go-between, and for t h e first time it was confirmed t h a t the detailed and continuous deep sea record of c h a n g e in magnetic field polarity could also be detected in sedimentary rocks found on land. T h e magnetic reversal record discovered in t h e thick, white limestone of Italy contained several surprises. First and foremost was t h e discovery t h a t for mote t h a n half of the 60-million-year Cretaceous Period, there were no magnetic reversals at all. Before this, it h a d b e e n assumed t h a t the c a d e n c e of magnetic pole reversal was rather c o n s t a n t , with a shift every half-million to million years or so, and indeed m u c h of t h e geological record reveals just this type of pattern. But for reasons still unclear, the m e c h a n i s m t h a t creates magnetic field teversals occasionally went on holiday. From about 118 to about 83 million years ago, t h e magnetic field was locked into n o r m a l polarity. Magnetostratigraphic dating is useless for this interval. However, t h e first reversal after this long interval of normal polarity is o n e of t h e most recognizable in the entire geological c o l u m n . T h i s "long n o r m a l , " as it c a m e to be called, was followed by a return to reversed and t h e n the restoration of norma! polarity in shorter intervals, w h i c h produced a readily recognizable "fingerprint" of polarity. A n y w h e r e on e a r t h where you know (from fossils or radiometric dating) that you are in t h e Cretaceous, and where you h a v e just received a reversed-polarity signal following a long interval of normal polarity,

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you know precisely where you are in t h e geological column: at 83 million years ago. T h e years of field work necessary to c o m p l e t e t h e m a m m o t h project of sampling t h e Italian A p e n n i n e s yielded more t h a n a detailed look at 100 million years of p a l e o m a g n e t i c reversals. It was from these sections that Walter Alvarez collected t h e clay samples t h a t yielded unexpectedly high conc e n t r a t i o n s of i r i d i u m — a n d led to t h e now-famous hypotheses t h a t the earth was struck by a large asteroid 65 million years ago and t h a t the global e n v i r o n m e n t a l effects of t h a t impact caused t h e Cretaceous/Tertiary mass extinctions, killing off an estimated 6 0 % to 7 0 % of all species t h e n on earth. An a n i m a t e d controversy arose a m o n g e a r t h scientists and lasted more t h a n a decade. Was this e x t i n c t i o n rapid and catastrophic or was it gradual, lasting millions of years? T h e s e two great pieces of w o r k — t h e d e m o n s t r a t i o n of a land-based section for studying Late Mesozoic and Cenozoic magnetic reversals linked to biostratigraphy, and t h e new theory about o n e of t h e greatest of all mass extinctions—caused a t r e m e n d o u s surge of intellectual excitement. Its epic e n t e r was Berkeley, where W a l t e r Alvarez worked. T h e late 1970s and early 1980s were aglow with t h e e x c i t e m e n t generated from these two pillars of research. T h a t glow readily made its way 90 miles east to t h e University of California at Davis, where I was still assistant professor of geology. I was swept up in b o t h fields, and I remain so to this day. T h e e x t i n c t i o n controversy was by far t h e more exciting. H o w could deciphering t h e age of west coast rock assemblages c o m p e t e with dinosaurs being snuffed out by cosmic collisions? Yet t h e e x t i n c t i o n controversy was being played out far away, on outcrops in Europe, and in a sense, the first step to understanding w h e t h e r t h e Alvarez theory was correct in determining the age of t h e rocks in question. Nevertheless, it was with some wistfulness that I resigned myself to working in t h e wings, while others lept to c e n t e r stage as t h e e x t i n c t i o n drama unfolded in nearby Berkeley. C h a n c e would soon c h a n g e t h a t for me. In t h e century since William G a b b had made the first discoveries of Cretaceous-aged rocks in California, so m u c h had changed. T h e Indians 56

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were gone, the rivercourses disrupted, t h e great interior valley turned from rolling grassland to farm. But some things had not changed: T h e California fossils were still e n d e m i c , and there was still very little understanding of how to correlate these west coast C r e t a c e o u s rocks with t h e standard reference sections in Europe. Because t h e fossils in these regions were n o t of t h e same species, it was impossible to use fossils as m e a n s of comparing t h e ages of the two regions. Yet the breakthroughs achieved in Europe and by t h e Deep Sea Drilling Program in t h e fields of integrated biostratigraphy and magnetostratigraphy offered a new key to t h e puzzle. A n d t h e n o n e of my new colleagues at Davis offered t h e opportunity. Professor Ken Verosub had graduated in physics from Stanford U n i v e r sity but had gravitated to t h e study of paleomagnetics. His initial suggestion that I might incorporate t h e t h e n relatively new field of magnetic sampling into more traditional biostratigraphic m e t h o d s got me started. At t h e time I had absolutely no idea h o w such sampling might take place. T h e Alvarez articles about sampling t h e A p e n n i n e M o u n t a i n s in Italy m e n t i o n e d only t h a t "oriented cores" were t a k e n from t h e rocks. But how? In my experience, cores were usually several inches thick and extracting t h e m required oilwell-drilling techniques. I envisioned large, t o o t h y metal bits being slowly screwed down through rock. Yet, t h e Italian work had required t h a t t h o u sands of "oriented cores" be obtained; and I knew t h a t thousands of oil rigs had not been marched over the Italian countryside. My i n t r o d u c t i o n to t h e tool designed to o b t a i n oriented cores was thus a pleasant surprise: It was a chain saw, but a c h a i n saw m u t a t e d s o m e h o w into a coring device. T h e chain and saw were gone; t h e m o t o r remained and was used to turn a hollow metal tube coated with d i a m o n d s , which cored t h e rock. This Rube Goldberg apparatus worked. T h e long tube attached to t h e motor was a small d i a m o n d drill about an inch in diameter. T h e m o t o r turns it at high speed, and the thousands of industrial-grade d i a m o n d s coating the tip are sufficient to cut several inches into any type of rock. T h e drill excavates a 2 - or 3 - i n c h core; this core is t h e n popped off with a chisel. If the exact attitude of the core is k n o w n ( t h e direction of its long axis and its angle of dip into the earth are measured with a compass), t h e n it c o n t a i n s all 57

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the information necessary for decoding t h e polarity of t h e earth's magnetic field at the time t h e rock was formed. Yet obtaining an oriented core is only the first part of the process of arriving at a n c i e n t magnetic directions. O n c e collected, t h e core must be analyzed in a large and complex m a c h i n e called a magnetometer. T h e intensity of t h e earth's magnetic field itself is small, and t h e a m o u n t of magnetic signal given off by t h e magnetite grains found w i t h i n a core 2 inches long and 1 inch in diameter is m i n u t e . T h e magnet o m e t e r was devised to measure these very tiny magnetic fields still existing within t h e cores. Like so m u c h in science, t h e theory is deceptively simple: An oriented core is extracted from some unsuspecting rock and t a k e n back to a laboratory. T h e r e it is put i n t o a gargantuan electrified m a c h i n e out of Baron v o n Frankenstein's worst n i g h t m a r e , and voila, a n u m b e r flashed on some computer screen tells you w h e t h e r t h e rocks from w h i c h t h e core was t a k e n were deposited w h e n the earth's polarity was normal or reversed. A n d , as in a lowbudget ad on TV, you get t h e s o m e t h i n g else t h r o w n in absolutely free—in this case, a m e a s u r e m e n t of t h e field intensity from t h e rocks you h a v e sampled and t h e inclination and d e c l i n a t i o n of the magnetic field from the age and locality you h a v e sampled. T h e s e latter bonuses can provide some of the most interesting information of all; they can tell you the a n c i e n t latitude of t h e rocks you h a v e sampled. I was seduced. At t h e time, no one had sampled Cretaceous-aged rocks for western N o r t h A m e r i c a , and t h e whole procedure seemed so sttaightfotward: Drill some cores, analyze t h e m , and end up with a polarity history t h a t could he m a t c h e d to t h e Italian wotk completed by Lowrie and Alvarez. W h y not? W h a t could go wrong? W h a t could be easier t h a n deciding in a binary system? All o n e needed to find out was w h e t h e r the fossil magnetic signal in t h e rocks reported a normal or a reversed polarity for any given time. W h o has n o t b e e n so seduced, be it for a used car, a V C R , or a new partner with no baggage? I took t h e bait, swallowed it, and headed off into the California hills with all t h e e q u i p m e n t needed to drill hundreds of small cores from t h e rocks. A n d everything w o r k e d — t h e first few times. (That's the secret of a really effective con: M a k e it work—at first.) 58

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It takes two to d r i l l — o n e to do t h e actual drilling, t h e o t h e r to p u m p the water. Water? S o m e h o w t h e water h a d n ' t c o m e up w h e n I received my first sales p i t c h from Dr. Verosub, w h o , like any good used-car salesman, also declined to spend any t i m e in t h e field actually drilling t h e tocks after our first trial run. T h e drilling requires t h a t copious q u a n t i t i e s of fresh water be p u m p e d c o n s t a n t l y t h r o u g h t h e drill while it is in c o n t a c t w i t h t h e rock. S p i n n i n g at propeller-like speed, it also emits t h e s c t e e c h i n g characteristic of c h a i n saws (but elevated in p i t c h because of t h e d i a m o n d on-rock c o n t a c t ) . I quickly found t h a t c o r i n g rocks for p a l e o m a g n e t i c sampling was a n y t h i n g but a rest cure. T h e drill h a d to be muscled i n t o place, and t h e coring of t h e rock, a c c o m p a n i e d by t h e c o n s t a n t stream of water being p u m p e d into t h e h o l e , e n v e l o p e d t h e o p e r a t i o n in a fine stream of muddy haze. T h e driller was soon c o a t e d w i t h wet m u d . T h r e e cores were taken at e a c h locality, and we drilled a n e w locality in e a c h m e t e r or in several meters of layered rock. Because our first sampling creek, C h i c o Creek, was over 500 meters t h i c k , we were s o o n locked i n t o a l o n g - t e r m endeavor. On a good day we could o b t a i n a b o u t 100 cores, but we often got less. Yet the drilling turned out to be t h e easiest part of t h e operation, for once the holes were bored into the rock, t h e cores h a d to be extracted and their orientation n o t e d . O r i e n t a t i o n was found by inserting a brass sleeve around the core (which, if we were fortunate, was still in t h e rock, a t t a c h e d at its base, and n o t broken off and j a m m e d inside t h e drill). T h e sleeve had a platform on top, which was m a c h i n e d so t h a t it held a geologist's compass. W h e n leveled, the compass showed t h e o r i e n t a t i o n of t h e core, and a second measurement yielded the plunge, or t h e angle of its e n t r a n c e into the rock. G i v e n these two observations, coupled with a m e a s u r e m e n t of t h e orientation of t h e sedimentary beds themselves (which sometimes were in their original, flat-lying o r i e n t a t i o n but more often were tilted at some angle, a complication t h a t had to be accounted for), a c o m p u t e r could calculate the original orientation of the core. All this took t i m e — t i m e to select a site, time to drill it, and m u c h time to take the accurate measurements necessary to arrive at core orientation. 50

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Because t h e drill was gas-powered, it needed c o n s t a n t refueling and lubrication. T h e drill bits t e n d e d to break. T h e water c a n was always in need of refilling. Even so, the hard work was relieved by its taking place on o n e of the most beautiful stretches of land in the wotld. C h i c o C r e e k had b e e n spared most of t h e ravages of the G o l d Rush. T h a t event, e v e n t h o u g h it occurred nearly 150 years ago, left ugly blemishes on t h e rivers of California t h a t still persist. In their mad quest for gold, the miners dredged tons of gravel and rock from t h e state's rivers and left these waste piles everywhere in t h e river valleys. T h e M o t h e r Load, in the foothills east of S a c r a m e n t o , was hardest hit, and those rivers of the north, such as t h e Feather and Touolome Rivers, were devastated as well. C h i c o C r e e k is a smallish creek flowing out of t h e Sierta N e v a d a foothills. It too had its share of gold, which, because of the rugged country around, was mined by h a n d rather t h a n by m a c h i n e dredges. But it has other treasures as well, treasures first discovered hy William G a b b . It has Cretaceous-aged fossils of spectacular beauty. T h e geological setting of C h i c o C r e e k is itself extraordinary. Most of the Sierran foothills in n o r t h e r n California are covered with dtab rock: thick, gray volcanic residue from t h e Sierras uplift blanket t h e older rocks in the region. O n l y where creeks and rivers h a v e cut deep gorges can t h e more a n c i e n t geology of this region be found. On C h i c o Creek, t h e high valley walls are made up of t h e thick volcanic rock, and only in the creek itself and in t h e low walls lining it are different rocks found, sedimentary rocks of m u c h greater antiquity. H e r e the creek has knifed d o w n into an a n c i e n t sea b o t t o m , where clams and snails and a m m o n i t e s in untold numhets lie entombed. T h e cool creek burbles merrily over this smooth, dark rock with its myriad white fossils, and e a c h year t h e flooding snow melt erodes t h e surrounding rock to bring n e w treasures into view, treasures that sparkle briefly before they too are eroded into sand grains on their way to the Pacific O c e a n . Gahb's pioneering expeditions to C h i c o Creek in t h e earliest years of the California Geological Survey showed the presence of Cretaceous-aged fossils in California, as we n o t e d C h a p t e r 1. A l t h o u g h G a b b could find no fossils similar to any species k n o w n from Europe, t h e prints of numerous am60

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monites belonging to t h e same genera, if not the same species, as European forms convinced h i m t h a t he was sampling n o t just Cretaceous-aged rocks, but upper Cretaceous rocks, equivalent in age to t h e chalk of the English and French coastlines. His collections were hurriedly made; he had, after all, an entire state to investigate, and no o n e portion, however physically beautiful, could monopolize his time. 1 le hoped that subsequent expeditions would reveal some a m m o n i t e species occurring in b o t h France and California, which would allow those two distant relics to be tied together by a filament of time. It was not to be. In t h e decades following Gabb's pioneering studies, t h e countless scientists and amateur fossil collectors w h o had b e e n drawn to t h e deep valley of C h i c o C r e e k by its rich fossil c o n t e n t searched in vain. For all the great collections subsequently amassed, no investigator stumbled on any fossil diagnostic ot the European Cretaceous. T h e great rampart of N o r t h and S o u t h America apparently created an impassable barrier for European species: T h e y could not colonize t h e new world of t h e Mesozoic Era. No species in Europe exchanged D N A during t h e Mesozoic Era w i t h any species in western N o r t h America, just as no mollusk species in these two areas do so today. If you take a paleontological specialist to see fossil collections made from deposits in t h e Pacific region, he or she will look in vain for old friends and will confront only strangers. Yet while t h e a m m o n i t e s and o t h e r diagnostic European fossils migrated westward with t h e currents over their myriad generations (ultimately to find more westward e x p a n s i o n blocked by geography), the earth's magnetic field created an indelible time marker in the C h i c o sedimentary rocks. T h r o u g h a great portion of the C r e t a c e o u s Period, w h i c h has b e e n radiometrically dated as beginning about 145 million years ago and ending 65 million years ago, t h e earth's magnetic field was stuck in o n e direction. T h e r e were no reversals for tens of millions of years. A n d t h e n , about 80 million years ago, this long quiescent period c a m e to an e n d with a reversal. A l though any teversal is a worldwide e v e n t , there h a v e b e e n so many t h r o u g h earth history t h a t a reversal is essentially useless w i t h o u t other, t i m e - b o u n d data such as those obtained through fossils or radiometric decay. But t h e first reversal of the Cretaceous "long n o r m a l " episode was a diagnostic fingerprint (.1

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t h a t could be used with only a m i n i m u m of o t h e r age control. All you needed to k n o w was t h a t you were sampling somewhere in the upper Cretaceous Period—a time interval itself more t h a n 30 million years long. If you t h e n e n c o u n t e r e d a zone of reversed magnetic polarity sitting atop a long interval of normal polarity, you could be assured of h a v i n g found the single most agediagnostic m a g n e t i c e v e n t in t h e history of the earth. T h i s magnetic reversal was given t h e u n r o m a n t i c n a m e of 33R. It was k n o w n from the deep sea and from t h e Italian A p e n n i n e s M o u n t a i n work. In 1980, analysis of my drill cores from C h i c o C r e e k showed it there too. Like an elusive fish finally hooked, t h e C r e t a c e o u s of t h e west coast of N o r t h America now had a l i n e — i n this case a time line—securely attached to the global time scale. A c c o r d i n g to K e n Verosub, w h o analyzed t h e cores drilled from C h i c o C r e e k sediment in his paleomagnetics lab at t h e University of California at Davis, t h e magnetic signal captured in our cores was strong. But was it accurate? Did t h e signal e m a n a t i n g from these rocks record t h e directions of the earth's magnetic field from a t i m e w h e n dinosaurs roamed t h e earth in profusion, or was it from a more recent time? In t h e lab, I learned that paleomagnetics is fraught with uncertainty and t h a t t h e black and white reversal p a t t e r n s shown on all summary charts of the earth's magnetic field history— apparently so clean and unambiguous in their binary glory—are really anyt h i n g but. Like so m u c h else, paleomagnetics sounds simple in theory. T h e sedim e n t s we h a d drilled from C h i c o C r e e k were sandstone and siltstone deposited on shallow sea b o t t o m s long (but exactly h o w long ago?) ago. A m o n g t h e m i n u t e sand and clay particles drifting d o w n o n t o that ancient sea b o t t o m were trillions and more of m a g n e t i t e grains; all were eventually squished together into t h e b o t t o m sediment. T h e last thing these tiny magn e t i t e grains did before being c e m e n t e d into place was orient themselves parallel to t h e earth's magnetic field. Each core so laboriously drilled from the rocks held some n u m b e r of m a g n e t i t e grains, and each core thus exhibited a tiny but measurable m a g n e t i c field of its own, created by its enclosed magnetite. Fed t h e o r i e n t a t i o n of a core, t h e m a g n e t o m e t e r could tell us the o r i e n t a t i o n of t h e magnetic field e m a n a t i n g from it. O n e by o n e , the inch62

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long cores were placed in t h e m a g n e t o m e t e r , itself a curious c o n t r a p t i o n of iron and wires resembling a 6-foot r o u n d e d coffin. Eventually t h r e e n u m bers emerged: t h e strength of the m a g n e t i c signal carried w i t h i n each core and ( w h e n t h e various attitudes of t h e core and t h e sedimentary beds were sorted out by t h e c o m p u t e r r u n n i n g t h e m a g n e t o m e t e r ) t h e declination and inclination of the earth's m a g n e t i c field at t h e time t h e rock t h a t had been cored solidified. T h e s e precious n u m b e r s revealed w h e t h e r t h e field at t h a t time was normal (like today's) or reversed. T h e numbers from C h i c o C r e e k showed b o t h normal and reversed polarity. I was jubilant: We had made t h e first discovery of polarity reversal in Mesozoic-aged rocks collected from the west coast of N o r t h America. But were these results "real"? Were they indeed a magnetic signature frozen in stone since t h e Mesozoic Era, or were they merely an artifact of later magnetism imprinting itself on these rocks? T h i s was t h e first inkling I had had t h a t paleomagnetism was n o t so simple a tool to operate as I had anticipated. It was explained to me t h a t the magnetic signal frozen in t h e sediments we had s a m p l e d — o r in any o t h e r rocks, for t h a t m a t t e r — m a i n t a i n e d its original direction only as long as the rocks were n e i t h e r reheated n o r subjected to a great deal of ground water passing through their pores. If t h e rock had b e e n reheated e n o u g h , t h e tiny magnetic rods of m a g n e t i t e t h a t had so faithfully recorded t h e a n c i e n t magnetic field present at their consolidation into this particular sedimentary rock would h a v e reoriented themselves to t h e direction of earth's magnetic field at the time of reheating, and they would h a v e d o n e so w i t h o u t leaving any clue. T h e r e would be no sign saying, in effect, " W e h a v e been reheated! We now give spurious results! Paleomagnetist beware!" H u g e mistakes c a n be made. T h e y h a v e been m a d e and will be made again. A n d is that the end of it? N o , there is more. M u c h of the time, the rocks you sample h a v e been heated, all right, but n o t quite to t h a t magic temperatute (called the Curie point) where the magnetic direction resets. Instead they take on a slight, but n o t complete, overprint of new magnetic field direction. In these cases the investigator must strip off this overprint, either by progressively heating t h e cores in an o v e n and r u n n i n g t h e m again, or by subjecting t h e m to an alternating electric field t h a t (sometimes) accomplishes 65

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the same result. You might say the paleomagnetist has to cook t h e data. A n d there is still more! Lots of rocks h a v e no m a g n e t i t e , or magnetite is present in such vanishingly small quantity t h a t t h e standard m a g n e t o m e t e r c a n n o t detect the a n c i e n t magnetic field. In this case a new instrument must he employed, a superconducting instrument t h a t has extremely high sensitivity. Thankfully, the C h i c o C r e e k cores showed no such problems. According to my learned paleomagnetist colleagues, they "behaved" beautifully: T h e y h a d a strong signal, showed b o t h normal and reversed polarity, and seemed to h a v e no overprint. W i t h m i n i m a l laboratory effort we attained publishable and very interesting results. We were able to identify the Cretaceous "long n o r m a l " and t h e first reversal above it. For the first time, rocks from t h e west coast of N o r t h A m e r i c a could be reliably dated and correlated with European stages and deep sea sediments. I was converted. T h i s m e t h o d seemed too good to be true. You guessed it. It was. O v e r t h e n e x t two years, Jim Haggart and I scoured the eastern and western sides of t h e G r e a t Valley sequence, drilling rocks and collecting ammonites. We helped tie t h e local California strata and its enclosed a m m o n i t e biostratigraphy to t h e international time scale. T h e r e were no ashes for us to date, so t h e r e was no way to find absolute ages. But t h e long normal polarity followed by this first reversal was a time marker almost without peer in the geological record. S o o n after our confirmation of this reversal in Cretaceous rocks of n o r t h e r n California, my colleague David Bottjer and others from southern California located it as well. I was spoiled by this early success. We seemed to be on t h e verge of a major breakthrough in telling time in western N o r t h A m e r i c a . But the process was so convoluted! We needed to compare t h e age of t h e rocks in California with those of the Vancouver Island region and t h e n c o m p a r e b o t h with t h e regions in Europe where the various time units were first identified. T h e s e European "standards" of comparison are called stratotypes. We could do this if we could rind a m m o n i t e or other fossil species t h a t had lived in b o t h places. But n o n e had! We ourselves could make the comparison if we could find rocks in b o t h regions t h a t could be radiometrically dated with a mass spectroscope. But n e i t h e r Europe nor the Vancouver Island region h a d t h e necessary b e n t o n i t e s (ash layers) in64

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terbedded with the sedimentary rocks, so t h a t approach was out. O u r last hope was t h e use of paleomagnetics. But o n c e again we were stymied. T h e rocks in Italy t h a t W a l t e r Alvarez a n d his colleagues h a d drilled h a d no ammonites. To complete t h e circle, to make possible t h e correlation, someone had to complete paleomagnetic analysis on European rocks with b o t h microfossils and a m m o n i t e s and t h e n c o m p l e t e the same type of paleomagnetic sampling in t h e Vancouver Island region. O n l y o n e suitable place was k n o w n to me in all of Europe: a region I had first visited in 1982 while researching a n o t h e r scientific question, t h e reason for t h e mass e x t i n c t i o n at the end of the Cretaceous Period. T h i s place was a seacoast section in Spain k n o w n as Zumaya. T h u s an ambitious plan was born. I decided to head east, to Zumaya, to core rocks in the classic European regions and t h e n head n o r t h w a r d and try it out on the rocks of t h e Vancouver Island region, including Sucia Island. Little did I know that I was approaching a problem already ruled intractable by workers far more experienced in t h e way we do magnetic rock analysis. I had enjoyed beginner's luck with t h e paleomagnetic time m a c h i n e . I was about to learn t h a t this particular time m a c h i n e was a very delicate apparatus indeed.

C a l i b r a t i n g our c l o c k s We struggled into t h e Madrid airport in early May of 1984- H a v i n g t a k e n an all-day flight from San Francisco to N e w York and t h e n h a v i n g flown all night from N e w York to Madrid, my friend Jeff M o u n t and I, a t w o - m a n expedition, numbly dragged a heavy w o o d e n crate from t h e i n t e r n a t i o n a l to the domestic air terminal. T h e crate held two paleomag drilling units and all the ancillary and peripheral gear needed to c o n d u c t t h a t research. O u r goal on this trip was simple: Rettieve a detailed history of t h e magnetic reversal stratigraphy from a classic o u t c r o p at Zumaya, Spain. H e r e we would be duplicating the paleomagnetic records of this tegion made in Italy by Walter Alvarez and William Lowrie a decade earlier. But our rocks c o n t a i n e d something precious t h a t is w a n t i n g in Italy: larger fossils, including a m m o n i t e s . 65

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Here, if we could o b t a i n a reliable paleomagnetic record, we could correlate the biostratigraphic markers of t h e latest Cretaceous, as recorded by amm o n i t e fossils, with t h e paleomagnetic reversal record. We had boarded t h e plane on a breathtakingly h o t California day, and Jeff traveled in shorts. By N e w York he was shivering, by Spain a vicious cold had t a k e n h i m — a rhinovirus assault of some gravity. But w h o in his thirties surrenders to a cold after traveling thousands of miles to finish a great deal of work in a short time? As t h e days w e n t by he got sicker and sicker, and still we worked. Up at 6 e a c h m o r n i n g , t h e Spanish excuse for a breakfast (strong coffee and a length of French bread and b u t t e r ) , and t h e n o n t o t h e outcrop. T h r o u g h t h e coastal village of Zumaya, we guided our small rental car t h r o u g h t h e tiny lanes scraping by old brick and plaster buildings, past the haystacks to t h e isolated coastal exposures. Drag t h e drill o n t o t h e rocks, fill t h e gas t a n k and t h e large water canister necessary to cool the drill, find the last site from t h e day before, and begin drilling anew. Spring is t h e time of squalls in the Bay of Biscay, rapidly moving blusters of wind and rain gathering from t h e south and belting the coast. We would try to find shelter at first, but eventually we just kept working, huddling undern e a t h our raincoats during the worst of squalls, hoping for the brief islands of sun in t h e ocean of clouds above. Day by day our sites marched down the b e a c h — a n d d o w n section. We started at the Cretaceous/Tertiary boundary, the site marking t h e great mass e x t i n c t i o n t h a t ended the Age of Dinosaurs, a site visible at Zumaya as a distinct lithological change. A n d t h e n we dropped, layer by layer, into ever older rocks, drilling every few meters going down this enormous c o l u m n of stacked limestone and marl, passing down a million years, and t h e n two, heading layer by layer, page by page of this stratal book, toward ever older oceans, eventually reaching rocks I t h o u g h t to be the same age as Sucia Island, but w h o knew? W i t h these cores, however, we might know. We would be t h e first; we would tie G u b b i o to Zumaya to Sucia Island in a web of magnetic correlation and time lines. For 10 days we drilled t h e coastal exposures. T h e r e was o t h e r work as well, of course. We collected fossils and we studied t h e Cretaceous/Tertiary boundary, searching for evidence t h a t a large cometary collision 65 million 66

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years ago did indeed end t h e A g e of Dinosaurs. But t h e primary goal here was to bring h o m e several h u n d r e d magnetic cores for paleomagnetic analysis. We flew h o m e , finally, laden with rocks and t h e many cores. W i t h impatience 1 awaited t h e paleomagnetic results. First, t h e cores h a d to be trimmed, and t h e n o n e by o n e they were fed into t h e magnetometer, over and over, as many as 10 times per cote. It soon b e c a m e discouragingly clear the these cores were far more compromised by m a g n e t i c overprint t h a n anything we had collected in California; in fact, it turned out t h a t none of the cores was useful for paleomagnetics. T h e s e rocks h a d apparently b e e n reheated, the small magnetic crystals in the cores realigned with a m u c h younger magnetic field. T h e weeks of work were for n a u g h t . We had h o p e d that the Spanish rocks would h a v e the same pristine magnetic signal as those from California, hut we were wrong. Several years later, Dr. Jan Smit of Holland would try again to drill Zumaya. I told h i m about our d i s a p p o i n t m e n t . Yet he too refused to believe t h a t these rocks would n o t yield good paleomagnetic results. He too understood t h e i m p o r t a n c e of learning t h e position of the paleomag reversal in t h e uppermost Cretaceous at Zumaya. A n d he too would conclude, as I had, t h a t a m a g n e t i c overprint had forever destroyed the primary magnetic signal h e t e . T h e r e is no publication of negative results of this kind. T h e work in Spain taught me a hard lesson. Magnetic clocks are reliable only in special circumstances. W h e n they work, they are superb. But there is no way you can go up to an outcrop and be sure t h a t you will obtain results. By the end of 1984, a magnetic reversal h a d b e e n identified from t h e Cretaceous of California. But the N a n a i m o G r o u p still tightly guarded t h e secret of its age. O t h e r workers before me had tried to extract its magnetic time secrets; others had tried to use t h e time m a c h i n e of a magnetic clock. No o n e had succeeded. Spain had taught me c a u t i o n , and I wondered whether magnetic sampling of Vancouver Island was worth t h e effort. But the reward if it worked! Magnetic analyses tell you more t h a n time: T h e y can pinpoint the a n c i e n t position of t h e rocks you study, t h e latitude at which the sedimentary or volcanic rocks solidified. T h e y c a n be the best tool of all for fixing place. T h e rocks we had drilled in California and Spain had 67

Correlation of Cretaceous stages, reversal time scale, and radiometric ages.

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not moved since they were deposited long ago in t h e Cretaceous, many previous investigators had concluded. S u c h was n o t t h e case for the Vancouver Island region. During t h e 1980s it was proposed t h a t t h e N a n a i m o G r o u p may h a v e originated far to the south of its present position and moved up t h e coast by plate tectonics, t h e m e c h a n i s m t h a t causes large blocks of t h e earth's crust to travel vast geographic distances over time. T h e best way to accept or refute t h i s — t h e best time m a c h i n e to use—was again paleomagnetics. N o w I had two reasons to succeed in my drilling plans for the Vancouver Island region. I still wanted to k n o w about time. But n o w I wanted to know about place as well. T h e story of t h e p a l e o m a g n e t i c analysis of t h e California C r e t a c e o u s aged strata is but o n e e x a m p l e of h o w this routinely used m e t h o d unfolds. Most such studies proceed in fits and starts, just as ours did. O n l y slowly does information a c c u m u l a t e , but it yields some of t h e best ways in our arsenal of time m a c h i n e s to find t h e age of rocks. Magnetostratigraphy, as this m e t h o d is called, is now used on virtually every time interval of t h e geologic record.

The solution Twenty years after b e g i n n i n g a seemingly simple quest, I could finally propose an age for t h e Sucia Island fossils. T h e Sucia strata bear t h e a m m o n i t e s Baculites a n d , more i m p o r t a n t , a heavily o r n a m e n t e d a m m o n i t e called Hopluoplacenticeras. T h e s e tell us t h a t Sucia Island is C a m p a n i a n in age and therefore is of the same age as t h e rocks in western France where t h e world's finest C h a m p a g n e is created. T h e species of Baculites is B. inornatus, which is also found in California. In a few creeks, this a m m o n i t e is found at t h e top of magnetozone 33R, t h e first reversal after t h e C r e t a c e o u s long normal. In the Western Interior Seaway, this same reversal has b e e n discovered in what is k n o w n as the Middle C a m p a n i a n . Its upper parts are filled with b e n t o n i t e s that have been dated b e t w e e n 81 and 79 million years in age. T h i s , t h e n , is the age of Sucia Island.

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The surface of the e a r t h seems so fixed. A n d it is, in our short lives. But if we take a m u c h longer view, we see t h a t t h e earth's surface is actually quite mobile. Fot any locality on earth we c a n ask, " H o w long has this place been at this place?" For some decades n o w t h e Vancouver Island region, this book's long-running example of how the various time m a c h i n e s work, has been suspected of being a "suspect t e r r a n e " — a place t h a t arrived at its current geography t h r o u g h c o n t i n e n t a l drift. A n d as it turns out, t h a t suspicion was well founded. T h e story of h o w we reached this c o n c l u s i o n — t h e time machine we used to do so—is t h e subject of this chapter. T h e story, from my point of view at least, begins on a small C a n a d i a n island n o r t h and west of Vancouver. 75

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Hornby Island Islands always h a v e their o w n flavor. M u c h of it comes from such disparate elements as topography, climate, vegetation, and fauna. But the h u m a n inh a b i t a n t s also subtly (or n o t so subtly) c h a n g e t h e feel of an island, especially if it becomes a h a v e n for t h e iconoclasts w h o sometimes make this world so interesting. H o r n b y Island of t h e C a n a d i a n Gulf Islands is definitely such a place. It is situated b e t w e e n Vancouver Island and t h e mainland of British C o l u m b i a , a medium-sized isle about 5 miles across. Like so many other of the islands in this region, it lies in rain shadow and h e n c e enjoys some of the best climate (and least rainfall) of any region of British C o l u m b i a . A n d perhaps for t h a t teason alone it attracted a great t h r o n g of t h e attists, hippies, nonconformists, radicals, and dropouts w h o h a v e made this and the other islands in t h e lee of Vancouver Island t h e California of C a n a d a . My o w n first visit to t h e place was in 1974. A l o n g the n o r t h shote of H o r n b y Island, a thick assemblage of nearly flat-lying mudstones contains some of t h e best-preserved a m m o n i t e fossils in t h e world, and I longed to see these famous beds, with their famous fossils. I was n o t disappointed. N e v e r really c o m m o n , the a m m o n i t e s from H o r n b y Island occur in nodules, or concretions, and t h e way to find t h e m is to crack o p e n these nodules. U n fortunately, only o n e nodule out of m a n y holds an a m m o n i t e (or some other fossil). T h e y are young for a m m o n i t e s . T h e quiet muddy sea b o t t o m from w h e n c e they come was deposited some time after the Sucia Islands beds and p e r h a p s — p e r h a p s — a b o u t 5 million years prior to the great comet impact that wrecked the Mesozoic world, killing dinosaurs, ammonites, and much else in the process. Yet t h a t e v e n t was still far in the future when the ammonites lived and died in the Hornby region. T h e Hornby Island ocean was an a m m o n i t e heyday, a last h u r r a h . On land t h e great dinosaurs still held sway, and the first Tyrannosaurus rex and Triceratops were evolving as the Western Interior Seaway of N o t t h A m e r i c a gradually receded from t h e continent. In the contemporaneous late Mesozoic oceans, shelled cephalopods and mosasaurs, archaic fish and bizarre flat clams, tropical reefs made of clams in74

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stead of corals—creatures great and small were alive. N o w they are but stony memories. My first trip to this island was brief: 1 blasted the concretions with my hammer, 1 found a few beautiful fossils, I spent a glorious day on a glorious beach, and 1 left, just a solitary day-tripper. 1 would n o t return for 12 years. I had gathered some fossils, but I had n o t d o n e any science. I was n o t really interested in t h e age of H o r n b y Island, or in m u c h else about it, at t h e time of my first visit. T h a t state of affairs was to c h a n g e greatly by my next. By early 1986 I had already learned t h a t paleomagnetism, seemingly such a simple and straightforward endeavor, was fraught with difficulty. If the sampled rocks had been reheated to any significant degree, you could n o t expect reliable results. T h o s e scientists w h o h a d sampled for paleomagnetism in the Cretaceous-aged strata of Vancouver Island concluded t h a t t h e entire region h a d been reheated and was therefore unsuitable for paleomagnetic work. But had the previous workers exhausted all avenues? H a d they shown without a doubt t h a t no region of t h e vast Vancouver Island area was unaffected by regional heating? I t h o u g h t t h a t the easternmost islands of the Georgian Strait might possibly be unaffected, because t h e a m m o n i t e s there were absolutely pristine. Like Sucia Island, H o r n b y had preserved its fossils well. Might n o t it h a v e preserved a primary magnetic signal too? It was worth a try, so I journeyed there with two s t u d e n t field assistants to drill for paleomagnetism. T h e trip took place in perfect weather, a late summer lark. We arrived on Fossil Beach, repository of so many exquisite ammonites, and began the laborious process of drilling and recording our results. S u c h activity certainly drew attention. Screaming like a banshee, throwing streams of muddy water out of the nozzle, a paleomag drill set is a raw wound walking. Lots of natives came by to see what in the world three mud-spattered m e n were doing on their beach. Island folk being the friendly people they usually .ire, we were soon befriended by a long-legged w o m a n , w h o graciously invited us to camp on her nearby property. Early each m o r n i n g we v e n t u r e d from this cozy spot, packing lunches and dirty clothes, and managed to remove more t h a n a h u n d r e d

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oriented cores, e a c h about an inch long, from t h e solid rock t h a t makes up the fossiliferous shale of H o r n b y Island. On t h e third day the infernal din of our drilling was overshadowed by an e v e n louder noise: A Royal C a n a d i a n M o u n t e d Police helicopter landed on our c a m p i n g spot and proceeded to root out m u c h of the shrubbery. It was t h e a n n u a l H o r n b y Island pot raid. M o n t h s later t h e slow analysis of t h e magnetic cores was completed, and it was as if we had b e e n smoking t h e pot growing so plentifully on H o r n b y Island, for many of t h e magnetic numbers seemed to make no sense. Cores t a k e n from adjacent beds gave wildly fluctuating results. S o m e cores were s o m e w h a t "well-behaved" ( t h e e u p h e m i s m employed by paleomagnetists for magnetic results t h a t show some semblance of orderly change w h e n analyzed). Most, however, were far more chaotic. A c c o r d i n g to Ken Verosub, w h o h a d b e e n involved in my earlier work in California and Spain, the numbers were too scrambled to be publishable. 1 t h o u g h t t h a t more t h a n a few of t h e cores betrayed t h e presence of t h e telltale reversals, but I was overruled. Even more vexing, t h e grant t h a t funded this project expired, and no more analysis could be run. O n c e again I h a d completed a project in w h i c h all of t h e immense work involved in collecting the cores was for naught, or so it seemed. O u r results from this expedition were never published. I h a d to leave t h e Vancouver Island rocks where they lay. But the revolution in t h e e a r t h sciences called plate tectonics, or c o n t i n e n t a l drift, was about to m a k e H o r n b y Island a pivotal place in o n e of the most interesting of all scientific controversies. C e n t r a l to this would be the magnetic record from H o r n b y — a n d yet a n o t h e r time m a c h i n e .

C o i n c i d e n c e o r c o n t i n e n t a l drift? T h e green, fossiliferous shale exposed on Sucia, Hornby, and t h e o t h e r islands of t h e Vancouver Island region—rocks grouped together by their comm o n age and o r i g i n — m a k e up a terrain t h a t in many ways seems iconic of t h e Pacific N o r t h w e s t . W h o could deny t h e nativeness of this land d r e n c h e d with rain, carpeted with fir trees, ferns and clinging moss, and surrounded by cold green seas o n c e filled with salmon and halibut (riches n o w supplanted 76

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by fishing boats chasing a dwindling stock)? Yet far to t h e south, along the sun-drenched coastline of Baja California, lie sedimentary strata identical in lithology and fossil c o n t e n t to t h e drab green mudstones so typical of the Upper Cretaceous of t h e Vancouver Island region. C o i n c i d e n c e ? Or c o n t i nental drift? C o n t i n e n t s do drift. W h o would deny t h e a n c i e n t love affair of Africa and S o u t h America, hoary c o n t i n e n t s t h a t long ago dallied in t h e i t global bed until they were torn asunder by a restive earth. Cerebral researchers needed complex m a c h i n e s to confirm t h e theory of c o n t i n e n t a l drift. But the ultimate evidence stares out at us from any m a p . We k n o w now t h a t t h e continents lie embedded in a p a v e m e n t of more dense oceanic crust and t h a t both crust and c o n t i n e n t s skate across t h e surface of t h e e a r t h on a more astringent and liquid interior. T h e s e truths are n o w accepted hy all earth scientists (the last holdout, Al Meyerhoff, has died). T h i s revelation ushered in one of t h e most profound scientific revolutions of our time, rivaling those sparked by D N A in biology and by relativity and q u a n t u m m e c h a n i c s in physics. A n d as often h a p p e n s after scientific tevolutions, o n c e the battle was over and t h e defenders of c o n t i n e n t a l immobility routed t h r o u g h evidence marshaled ffom paleomagnetics, paleontology, and paleoceanography— in short, o n c e the p r o p o n e n t s of c o n t i n e n t a l drift had w o n — t h e victors, like so many conquering armies, claimed t h e spoils of war a n d w e n t a little overboard. In the aftermath of victory, every feature on t h e earth was seen as resulting from some plate t e c t o n i c process. If c o n t i n e n t s could move, why not every other feature on this wrinkled and a n c i e n t earth? A blizzard of speculative papets about a n c i e n t c o n t i n e n t a l configurations blanketed t h e landscape. Hypotheses outstripped the ability, a n d e v e n t h e desire, to test t h e m . Backlash set in. Q u i t e properly, e a r t h scientists began to d e m a n d c o n v i n c i n g proof rather t h a n merely hypotheses c o n c e r n i n g c o n t i n e n t a l drift a n d t h e a n c i e n t continental positions. Yet proof was often quite difficult to assemble. T h e original evidence confirming t h e theory of c o n t i n e n t a l drift came mainly from ocean basins, n o t c o n t i n e n t s ; it was t h e ocean basins t h a t revealed their long, linear underwater m o u n t a i n chains, t h e spreading centers where 77

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new oceanic crust is formed. T h e s e same ocean basins that yielded the magnetic lineations on t h e b o t t o m of t h e sea, showing that ocean crust is ever more a n c i e n t as we m o v e away from t h e spreading centers. It was the ocean basins t h a t revealed t h e presence of subduction zones, t h e linear regions where t h e conveyor belt of crustal m o v e m e n t dives under c o n t i n e n t s , to be consumed by t h e earth's interior h e a t and t h e n move back toward the spreading centers along e n o r m o u s lithic c o n v e c t i o n cells that power contin e n t a l drift. From t h e c o n t i n e n t s far less information is available. At least as far as proofs of c o n t i n e n t a l drift are c o n c e r n e d , t h e best evidence comes mainly from t h e t i m e m a c h i n e s of stratigraphic analysis and paleomagnetics. Stratigraphy is t h e simplest b r a n c h of the e a r t h sciences, at least in principle. Stratigraphers study t h e sequence of rocks as they pile o n e upon a n o t h e r t h r o u g h time. S o m e t i m e s a stratigraphic succession is created by the simplest action of o n e sand grain falling upon a n o t h e r over time, leaving beh i n d sedimentary beds, oldest on t h e b o t t o m , youngest on top. Sometimes things are far more complicated, a n d great slices of earth's crust are thrust over t h e tops of o t h e r huge slices. Yet e v e n in these complex tectonic cases, t h e order of things is deciphered via stratigraphy. O n e of t h e best ways to d e t e c t w h e t h e r o n e h u n k of rock on a contin e n t is related to a n o t h e r — o r e v e n to rocks on a different c o n t i n e n t — derives from stratigraphy. For example, o n e of t h e first (and still among the most powerful) lines of evidence used by early believers in plate tectonics came from stratigraphic studies c o n d u c t e d in t h e S o u t h e r n hemisphere. Investigators such as Alfred W e g e n e r and A l e x a n d e r du Toit recognized that similar successions of sedimentary rocks were observable on the n o w widely separated expanses of Australia, Africa, Asia, India, S o u t h America, and A n t a r c t i c a . Long before any believable mechanisms had been proposed to acc o u n t for c o n t i n e n t a l drift, S o u t h e r n h e m i s p h e r e geologists defined a diagnostic, quatter-billion-year-old succession of strata (which they named G o n d w a n a succession) and argued (mostly to deaf ears) t h a t such similar stratigraphic successions on c o n t i n e n t s now-separated could n o t be coincidence. All of t h e c o n t i n e n t s bearing these rocks must h a v e b e e n part of a sin-

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gle giant c o n t i n e n t a l land mass at t h e e n d of t h e Permian Period, about 250 million years ago. A n d so they were. T h e c o n c e p t of c o n t i n e n t a l drift was first given serious consideration in the late n i n e t e e n t h centuty, w h e n t h e then-famous A u s t r i a n geologist Eduard Suess suggested that Africa,

Madagascar, and India

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joined together as a single land mass and only later drifted apart. Suess based this heretical proposal on t h e great similarity in t h e rock types found in all three areas. He n a m e d this a n c i e n t c o n t i n e n t G o n d w a n a l a n d , borrowing the n a m e from an area in India inhabited by a tribe called t h e G o n d s . Suess was no charlatan or crackpot, a n d soon a few o t h e t geologists, mainly those working in the S o u t h e r n h e m i s p h e r e , began considering t h e possibility t h a t a " s u p e t c o n t i n e n t " existed there during t h e late Paleozoic a n d early Mesozoic Eras. T h e various threads of evidence supporting t h e concept of an ancient, southern supercontinent were woven together in a remarkable book published by the G e r m a n meteorologist Alfred Wegener in 1912. Wegener was convinced that the similarity in coastlines between western Africa and eastern South America went far beyond coincidence. He amassed paleontological and geological information to support his cause, hut his book was m e t with instant criticism. No mechanism for such "continental drift" could be postulated. In t h e early 1900s a young S o u t h African geologist n a m e d A l e x a n d e r du Toit began to crisscross S o u t h Africa. He was to spend 20 years e x a m i n ing rock structure, mapping huge expanses of territory, and, in t h e process, filing vast amounts of information away in his encyclopedic memory. Du Toit soon realized t h a t Wegener's outrageous hypothesis explained many of t h e geological features of s o u t h e r n Africa, and in 1921 he published his first paper about t h e possibility of " c o n t i n e n t a l sliding." Geologists had long b e e n puzzled about t h e origin of t h e m o u n t a i n s rimming t h e S o u t h African coastline. Du Toit realized t h a t they could h a v e b e e n compressed by c o n t i n e n t a l collision; he had a vision of s o u t h e r n Africa caught in a monstrous vice between S o u t h America and A n t a r c t i c a . Du Toit was able to visit o t h e r southern c o n t i n e n t s , where he observed remarkably similar successions of rocks. It

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was n o t just t h a t t h e rock types were t h e same; more convincingly, they showed a similar stratigraphy. Du Toit w e n t far beyond W e g e n e r in his understanding of G o n d w a n a land; he was able to imagine b o t h t h e early merging of t h e various c o n t i n e n tal pieces and their climactic melding into a single c o n t i n e n t a l mass in late Paleozoic time, followed by their fragmentation during the Mesozoic and Cenozoic Eras. He b e c a m e well versed in t h e stratigraphy not only of his own c o n t i n e n t but of t h e o t h e r members of G o n d w a n a as well. Perhaps his most telling argument supporting c o n t i n e n t a l drift was his d e m o n s t r a t i o n of t h e remarkable similarity a m o n g late Paleozoic rock sequences on the various c o n t i n e n t a l pieces. On each he saw a basal unit of rocks deposited during Ice Ages, k n o w n as glacial tillites, overlain by lake deposits c o n t a i n i n g a small aquatic reptile n a m e d Mesosaurus and t h e n by deltaic and river deposits; t h e units c u l m i n a t e d in Mesozoic-aged basalt. Du Toit called this the G o n d w a n a System, k n o w n today as t h e G o n d w a n a S e q u e n c e . W e g e n e r and du Toit turned out to be correct. But like V i n c e n t van G o g h , w h o never saw his genius acknowledged, n e i t h e r Wegener nor du Toit lived to see their great triumph of observation and reasoning confirmed. T h e proof t h a t c o n t i n e n t s wander did n o t burst into t h e scientific consciousness until t h e early 1960s, w h e n a slew of studies brought t h e theory of a static earth tumbling d o w n . First, studies on rock magnetism showed t h a t either the geomagnetic pole had moved t h r o u g h time or t h e c o n t i n e n t s had. Both seemed utterly impossible. But in short order, new e v i d e n c e supporting c o n t i n e n t a l drift came to light. It was d e m o n s t r a t e d t h a t t h e m i d - A t l a n t i c ridge, a t h e n poorly k n o w n line of undersea m o u n t a i n s r u n n i n g d o w n the middle of the A t l a n t i c O c e a n , was composed of a c h a i n of active volcanoes constantly in the process of creating new oceanic floor. N e x t , a newly instituted program of deep-sea drilling d e m o n s t r a t e d t h a t t h e age of the ocean floor increases as o n e moves away from these submarine volcanic chains, w h i c h oceanographers began to call "spreading centers"; this discovery proved t h a t the sea floor was spreading and that, in m a n y cases, it carried c o n t i n e n t s along for the ride. But where was all this n e w ocean floor going? Seismic studies then 80

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showed that in many places on earth, oceanic crust dips downward into t h e earth itself along long linear arcs of t h e earth's crust called subduction zones. Subduction invariably leads to m o u n t a i n chains and active volcanic m o u n tains inland of these features. A scientific revolution had occurred within a few short years. We n o w k n o w t h a t c o n t i n e n t s indeed h a v e drifted and that they drift still. T h e y do so because they float. All c o n t i n e n t s are masses of relatively low-density rock e m b e d d e d in a ground of more dense material; c o n t i n e n t s essentially float on a t h i n (compared with the diameter of the e a r t h ) bed of basalt. Earth scientists like to use the analogy of an o n i o n . T h e o c e a n crust c a n be likened to t h e t h i n , dry, and brittle o n i o n skin sitting atop a c o n c e n t r i c globe of higher-density, wetter material that itself is moving relative to t h e m u c h thicker interior of our global "onion." C o n t i n e n t s are like t h i n smudges of slightly different m a t e rial embedded in t h e o n i o n skin. U n l i k e an o n i o n , however, t h e e a r t h has a radioactive core and constantly generates great quantities of h e a t as t h e radioactive minerals, e n t o m b e d deep in t h e e a t t h , break d o w n into t h e i t various isotopic by-products, liberating h e a t in t h e process. As this h e a t tises toward the surface, it creates gigantic c o n v e c t i o n cells of h o t , liquid rock in the m a n t l e — a m o l t e n layer of material directly b e n e a t h t h e outermost region of the earth, t h e crust. Like boiling water, t h e viscous upper m a n t l e rises, moves parallel to the surface of the e a r t h for great distances at rates of several inches each year (all t h e while losing h e a t ) and t h e n , m u c h cooled, settles back down into t h e depths of t h e earth. T h e s e gigantic c o n v e c t i o n cells carry t h e t h i n , brittle outer layer of t h e e a r t h — k n o w n as plates—along with t h e m . Sometimes this outermost layer of crust is composed only of ocean bed. Sometimes, however, o n e or more c o n t i n e n t s or smaller land masses are trapped in the mewing outer skin. T h i s process, w h i c h is termed c o n t i n e n t a l drift or plate tectonics, is o n e of t h e great unifying theories of all science. T h e spreading centers produce new crust as giant plates drift apart. Yet these plates are n o t always diverging. T h e y also converge, sometimes causing the collision of great c o n t i n e n t s . T h e collision of two c o n t i n e n t s is a slow, majestic process each land mass moves at only a few centimeters pet year; so si

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thousands of lifetimes must pass before any c h a n g e in position would be apparent. But as millennia pass, t h e c o n t i n e n t s do m o v e relative to o n e another, and sometimes they collide. T h e first c o n t a c t of t h e opposing contin e n t a l shelves does little. But year after year, as t h e two giant c o n t i n e n t a l blocks of earth's crust coalesce, e n o r m o u s forces of compression act on the c o n t i n e n t a l edges until t h e outermost regions buckle. M o u n t a i n s begin to form along t h e two edges as t h e collision progresses, often creating high, spewing volcanoes amid t h e c o n t o r t e d mass of sediment and rock t h a t was o n c e a tranquil coastline of wide sandy beaches. Finally, the two c o n t i n e n t s are incapable of further compression, yet they are still driving against each other. Slowly, o n e of t h e c o n t i n e n t s slides over t h e other, often doubling the thickness of their crustal edges in the process; t h e n they lock together, no longer able to give any more ground. A relatively recent and dramatic example is t h e collision of India and Asia. Forty million years ago, India was a small fugitive of t h e a n c i e n t G o n d w a n a s u p e r c o n t i n e n t , fleeing northward from its origins in t h e S o u t h e r n h e m i s p h e r e until it collided with mainland Asia. In t h e process, t h e edge of t h e Indian c o n t i n e n t rode up o n t o the A s i a n mainland, resulting in t h e formation of t h e world's highest mountains, the Himalayas, w h i c h are composed of t h e thickest c o n t i n e n t a l crust k n o w n o n earth. Geologists k n o w n o w t h a t plates, those e n o r m o u s lithic fragments that do t h e drifting of c o n t i n e n t a l drift, can interact with other plates in only three ways: T h e y can pull apart, smash together, or run side by side. T h e first two p h e n o m e n a — t h e divergence of plates at t h e mid-ocean ridge spreading centers, a n d their c o n v e r g e n c e at subduction zones—were t h e subject of the first pioneering wave of plate tectonics research, w h i c h demonstrated the reality of c o n t i n e n t a l drift. Yet t h e third, t h e side-by-side m o t i o n of plate margins, is equally i m p o r t a n t . T h e S a n A n d r e a s fault in California is perhaps the best example of side-by-side m o t i o n . T h e San A n d r e a s has b e e n operating now for millions of years, and as t h e t h i n slice of California on t h e outboard side scrapes n o r t h w a r d , e a r t h q u a k e by earrhquake, it separates rock units that o n c e were geographically together.

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T h e San A n d r e a s fault and t h e trajectories of t h e two rock masses it sepatates also provide an excellent model for envisioning how many contin e n t a l margins interact. O n e of t h e great discoveries of t h e c o n t i n e n t a l drift model is that c o n t i n e n t s not only slide across t h e surface of the globe like lugubrious bumper cars, alternately smashing into and fleeing o t h e r continental entities, but also grow t h r o u g h plate t e c t o n i c processes. Small slivers of o t h e t land masses—islands and pieces of o t h e r c o n t i n e n t s — t h e s e lithological flotsam drift ashore and meld on t h e edges of larger c o n t i n e n t s through the long eons of time. A n d in t h e process, they inexorably enlarge various c o n t i n e n t a l bodies. N o r t h A m e r i c a n is no e x c e p t i o n to this steady c o n t i n e n t a l enlargem e n t . Starting as a central core of a n c i e n t rocks such as gneiss, gtanite, and schist several billion years ago, N o r t h A m e r i c a grew as successive waves of small lithic immigrants either accreted o n t o its coasts or became c e m e n t e d in place due to t h e collision of N o r t h A m e r i c a with some o t h e r c o n t i n e n t . A l o n g the eastern seaboard of N o r t h A m e r i c a , t h e A p p a l a c h i a n M o u n t a i n s swelled upward and outward, first by m o u n t a i n fotmation inland of active subduction zones, later by t h e collision of N o r t h A m e r i c a with Europe and Africa. M o u n t a i n s also grew in western N o r t h A m e r i c a , but differently t h a n in the east. Subduction took place, creating high volcanoes. But many more, smaller pieces of drifting crust collided and became accreted o n t o our wandering c o n t i n e n t . Exactly h o w and when such smallet pieces accreted o n t o the western coast of N o r t h A m e r i c a has been t h e source of e n d u r i n g dispute.

A territorial d i s p u t e Perhaps no block of this itinerant real estate has created so m u c h c o n t r o versy as the region encompassing Vancouver Island and W e s t e r n British C o lumbia. T h e conflict is ovet w h e t h e r this giant region was formed through the collision of o n e or more s u b c o n t i n e n t s smashing into t h e larger N o r t h Ametica coast and thus is the first and still-enduring example of what is now

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k n o w n as accretion tectonics. O n e side believes t h a t W e s t e r n British C o l u m bia has always b e e n in its present-day position. T h e o t h e r believes that all of this vast region drifted n o r t h w a r d during t h e A g e of Dinosaurs, finally to collide with t h e t h e n - w e s t e r n m o s t coastline of N o r t h A m e r i c a , producing the Coast Ranges of C a n a d a and the N o r t h Cascades of W a s h i n g t o n State. Plate tectonics gave us the overall view of h o w the largest pieces of the earth's crust, the c o n t i n e n t s and ocean basins, have interacted through time. Accretional tectonics tells us about c o n t i n e n t a l assembly and how coastal m o u n t a i n belts form. T h e controversy often arises from the simple fact that mountains are the most complex geological units on the planet. Because mountains are composed of rocks thrust and shattered, folded and heated, pressurized and flung high into the sky, they are usually impervious to simple structural analysis of their c o m p o n e n t parts. To put it more simply, the characteristic trauma of m o u n t a i n building destroys the evidence about their formation. M o u n t a i n s are formed by several processes, including compression, extension, and the eruption of volcanoes forming in response to subduction. But w h e n these processes are melded with accretional e v e n t s — s u c h as an island t h e size of Vancouver Island colliding with an already-forming coastal m o u n t a i n r a n g e — t h i n g s b e c o m e m u c h more complex. Today, the most researched aspects of c o n t i n e n t a l drift are related to the importance of such collisions between c o n t i n e n t s and t h e smallest crustal fragments accreting o n t o c o n t i n e n t a l edges. T h e s e e p h e m e r a l and active bits of land are called suspect terranes, because more often t h a n n o t their formation in this m a n n e r is h y p o t h e t i c a l — a n d usually controversial as well. J o h n M c P h e e , perhaps t h e greatest living writer on things geological, has visited t h e topic (as well as t h e real estate) of suspect terranes in several of his books. T h e y are wonderful subjects: regions where large pieces of m o u n t a i n chains are seemingly exotic, perhaps far-wanderers coalesced into more banal country rock. T h e y c o m e in various shapes and sizes, and to discuss t h e m we need some specialized terminology. T h e first important pieces of such puzzles is microplates. Most plates (the plate of plate tectonics) are e n o r m o u s affairs, covering significant portions of t h e earth's crust. It is o n e of t h e great geological mysteries why there 84

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should he so few plates m a k i n g up t h e surface of t h e e a t t h . N o r t h A m e t i c a , for instance, t h o u g h gigantic in itself, is only o n e piece of a plate t h a t also includes half t h e A t l a n t i c O c e a n . T h e plates t h a t m a k e u p t h e p r e p o n d e r ance of t h e vast Pacific O c e a n are e v e n larger. But interspersed a m o n g these h e h e m o t h s are smaller versions, t h e microplates. W h e n microplates and larger plates interact, q u i t e c o m p l e x geological e v e n t s c a n occur. Take, for e x a m p l e , t h e region a r o u n d Indonesia. It rests on a m i c r o p l a t e squeezed b e t w e e n t h r e e b e h e m o t h s : t h e I n d i a - A u s t r a l i a plate, t h e Pacific Plate, a n d the Eurasian plate. Australia at t h e p r e s e n t t i m e is m o v i n g forward, slowly squeezing all of t h e myriad island a r o u n d Indonesia into Asia in t h e process. T h e result is geological c h a o s : T h e collision is smashing volcanic island chains, sediment-filled basins, pieces of c o n t i n e n t a l matgins, o c e a n i c seamounts, and young oceanic crust i n t o t h e same geological blender. Each of these units is composed of its o w n rock type, and as they squish together and ooze over o n e another, a most complex assemblage is formed. S o m e pieces are raised upward, others are depressed and run over; m o u n t a i n s form, m o u n t a i n s are destroyed. Pity t h e poor geologists of 50 million years from

Subduction zone along the descending Pacific Plate.

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now (unless they h a v e a real time m a c h i n e ) trying to deduce the sequence of events. But just such chaos appears to be what formed the west coast of N o r t h A m e r i c a 50 to 100 million years ago, and pity poor us now trying to work it out. A second key unit is t h e terrane (more properly a "tectonostratigraphic terrane," but let's keep it simple). Terranes are collections of rock showing a particular stratigraphy t h a t is separated from o t h e r rock types by faults, or breaks in t h e rock. Microplates b e c o m e terranes w h e n they collide with other rocks and are fused o n t o c o n t i n e n t s . Terranes (and t h e suspect ones a m o n g t h e m ) h a v e several disparate origins. T h e y can be (1) fragments of c o n t i n e n t s , long since split off, composed of old sedimentary rock and perhaps granites and old m e t a m o r p h i c rocks; (2) fragments of c o n t i n e n t a l margins, w h i c h are usually composed of sediments shed from a c o n t i n e n t a l margin); (3) fragments of volcanic arcs, made up of accumulated lava and sediment; or (4) fragments of ocean basins, and thus m a d e up of basalt. Terranes may begin their existence by being "born" in some oceanic setting (such as t h r o u g h t h e a c c u m u l a t i o n of lava in a submarine setting), or they may form as they are "calved" off of some already existing land mass, t h r o u g h a process k n o w n as rifting. In e a c h case t h e accumulated rock is buoyant relative to oceanic crust, so it "floats" on heavier crust. Its fate, sooner or later, will be to collide with some o t h e r buoyant crust. S u c h collisions are t h e process t h r o u g h w h i c h c o n t i n e n t s often grow larger, for more often t h a n n o t , t h e colliding pieces accrete o n t o the larger land mass. But h o w c a n we deduce the antiquity of such an e v e n t , and h o w can we tell what t h e colliding pieces looked like, were m a d e up of, or came from before the collision? Stratigraphy is o n e powerful tool, as we saw in our discussion about t h e first recognition of t h e G o n d w a n a s u p e r c o n t i n e n t . But an even more useful tool comes from paleomagnetics. T h e r e has long b e e n an uneasy alliance between t h e two great pillars of the e a r t h sciences: t h e b r a n c h e s k n o w n as geology and geophysics. In the simplest sense, geology addresses history—when the observable features on and in t h e earth formed—whereas geophysics deals mainly with the physical 86

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forces that did the f o r m i n g — t h e fiou> and why. Geology is thus more concerned with time and geophysics with process, a l t h o u g h h o t h fields borrow from t h e other, and t h e distinctions b e t w e e n t h e m are a n y t h i n g but clearcut. Nevertheless, although they work most often in concert, t h e fields of geology and geophysics h a v e sometimes found themselves on opposite sides of fierce scientific debates. T h i s is especially true for two of t h e most important questions confronted by t h e geological sciences: H o w old is t h e earth? Do c o n t i n e n t s drift? W i t h regard to t h e age of t h e earth, t h e father of geophysics, t h e gteat Lord Kelvin, and his followers were certainly wrong, and these errors led many scientists astray for decades. T h e geophysicists made a similar, m o n u mental blunder w h e n it was originally proposed, in t h e first half of t h e twentieth century, that c o n t i n e n t s had drifted. T h e geophysicists simply could not conceive of a way in w h i c h such huge blocks of m a t t e r could sail across wide ocean basins. Geologists, especially geologists w h o studied t h e S o u t h ern hemisphere, such as W e g e n e r and du Toit, amassed tomes of stratigraphic and o t h e r evidence: t h e fit of t h e c o n t i n e n t s , t h e presence of similar fossils, and the similarity of rock types or succession on c o n t i n e n t s n o w widely separated. Today, these lines of evidence appear as incontrovertible as they did to the ardent and frustrated geologists of a half-century and more ago. Yet physics and its branches, of w h i c h geophysics is o n e , h a v e long assumed the m a n t l e of scientific supremacy. T h e geophysicists held firm in their v e h e m e n t opposition to c o n t i n e n t a l drift and, as in their stance concerning the age of rocks, retarded scientific progress for decades. This chastisement is offered as a prologue to irony: T h e shoe has traded feet. Now, in many regards, it is geology t h a t has accumulated blinders and geophysics that frets. T h e subject of c o n c e r n is still within the province of plate tectonics, but o n e subdivision thereof. T h e controversy involves suspect terranes and is focused on the formation and history of western N o r t h America. Perhaps the greatest single tool whose use eventually c o n v i n c e d geophysicists that the crust of t h e earth is at heart a wandering entity came from the study of rock magnetism. As we saw in C h a p t e r 3, any igneous or sedimentary rock solidifying for the fitst time usually c o n t a i n s tiny magnets t h a t 87

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can yield highly accurate information about b o t h polarity and geomagnetic field directions ( w h i c h are themselves dictated by latitude). T h e s e two bits of information b e c a m e crucial lines of evidence of c o n t i n e n t a l drift. In areas where new sea floor is being created at the mid-ocean spreading centers, a series of linear magnetic stripes of opposing polarity h a v e been measured by ships and planes towing sensitive air- or waterborne magnetometers. Second, t h e c o m m o n application of m a g n e t i c coring from c o n t i n e n t a l rocks showed t h a t different c o n t i n e n t s seemed to exhibit very different directions of the a n c i e n t m a g n e t i c poles. Successively older rocks in N o r t h America, for instance, seemed to suggest t h a t t h e position of t h e earth's magnetic pole has b e e n migrating. Of course, it was n o t t h e earth's magnetic dipole positions t h a t were wandering but the continents themselves. By tracing t h e m back t h r o u g h time, via paleomagnetism, detailed histories of drift could be obtained. S u c h was t h e up-side of paleomagnetic analyses. T h e down-side is t h a t rock units t h a t h a v e been reheated gives spurious results. Unfortunately, no easily observable sign alerts t h e investigator t h a t this has h a p p e n e d . T h e magnetic resetting of mineral grains occurs most frequently in those parts of the e a r t h where regional h e a t i n g and high pressure are most i n t e n s e — i n m o u n t a i n o u s regions. Because these are t h e regions t h a t are usually of greatest interest for deciphering a c o n t i n e n t ' s history, paleomagnetic work rarely yields a simple interpretation. T h e m o u n t a i n o u s regions harbor the various slivers and shards of crust formed by collisions of c o n t i n e n t s with o t h e r rock units, and it is in t h e m o u n t a i n s t h a t paleomagnetic studies are most urgently n e e d e d — a n d most perilous. W i t h i n a decade of victorious o v e r t h r o w of all preceding theories, global tectonics and c o n t i n e n t a l drift theory had revealed the p a t h of N o r t h America's drift over t h e last 500 million years ( a l t h o u g h many details still rem a i n to be discovered). But m u c h more mysterious is t h e history n o t of N o r t h America's drift but of its t e c t o n i c formation, and no region remains more obscure t h a n its west coast. S t r e t c h i n g from Alaska to southern Mexico, virtually t h e entire western margin of N o r t h A m e r i c a is mountainous. H o w did these m o u n t a i n s form? W e r e they the product of subduction only, 88

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where ocean crust dives under a c o n t i n e n t a l margin, melting (and creating a line of volcanoes on t h e surface) in t h e process? Clearly there were many volcanoes along t h e west coast of N o r t h A m e t i c a , and as t h e m o v e m e n t s of the oceanic crust was deciphered in t h e early 1960s, it hecame clear that many of the m o u n t a i n s of N o r t h A m e r i c a were indeed produced hy subduction. T h e high Cascade volcanoes of t h e Pacific N o r t h w e s t are an excellent example. Equally clear, however, is t h e fact t h a t this type of plate-to-plate contact, creating subduction zones, was n o t t h e only type of plate interaction going on. O t h e r processes of m o u n t a i n building h a v e b e e n taking place as well. Perhaps n o w h e r e are these latter types of plate i n t e r a c t i o n better studied t h a n in California. California is e a r t h q u a k e country. Earthquakes occur w h e n rocks m o v e . Most of California's earthquakes can be attributed to t h e type of plate-toplate m o t i o n k n o w n as strike slip. T h i s type of m o v e m e n t , wherein t h e edges of plates scrape by each other, is causing t h e westernmost portions of t h e G o l d e n S t a t e to move n o r t h w a r d . T h i s m o t i o n will c o n t i n u e until t h e various fragments, carrying San Francisco and Los Angeles on their backs, run into something, such as a n o t h e r part of t h e west coast of N o r t h A m e r i c a . It now seems probable t h a t m u c h of western N o r t h A m e r i c a was created by collisions with smaller, s u b c o n t i n e n t - or island-sized land masses, forming m o u n t a i n s in t h e process. We are witnessing t h e start of o n e such voyage; its destination is still u n k n o w n . S a n Francisco a n d t h e long sliver of land it sits on will, over the n e x t few millions of years, leave N o r t h America's embrace to become a long borderland west of t h e c o n t i n e n t , thereby creating an inland sea. S o m e t i m e in t h e far future, it will probably collide with N o r t h America again. T h i s seems to h a v e b e e n t h e t e c t o n i c style for westernmost N o r t h A m e r i c a for several h u n d r e d s of millions of years: Land masses large and small h a v e b e e n m o v i n g n o r t h w a r d and colliding with western N o r t h America, becoming part of the c o n t i n e n t s in the process, or sometimes c o n t i n u i n g their n o r t h w a t d journey. Geologists h a v e deciphered this history n o t only by studying t h e S a n A n d r e s fault complex, but also, where possible, by c o n d u c t i n g paleomagnetic analyses for various bits of N o r t h America. 89

Locations of craton, disrupted craton, and suspect terranes in Western North America. Major fault zones and respective movements along these faults also illustrated.

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For more t h a n a century, deciphering t h e tangled, complicated mixture of rocks that make up western N o r t h A m e r i c a has b e e n t h e career choice (or fate) of hundreds of the best e a r t h scientists. T h e y h a v e needed to be smart: T h e variety of assemblage a n d style seemed i n c o m p t e h e n s i h l e for a long time. T h e emergent theory of plate t e c t o n i c s — a n d especially t h e new tool of terrane analysis using p a l e o m a g n e t i s m — s e e m e d at last to offer a way out of this morass. T h e observed direction of n o r t h w a t d t e c t o n i c m o v e m e n t in the present-day California coast region supplied a key clue to h o w t h e coast had formed. Earth scientists began to wonder if m u c h of t h e west coast of N o r t h America had not formed far to t h e south, as small islands or subcontinents, and t h e n b e c o m e accreted o n t o t h e c o n t i n e n t . In t h e early 1970s, teams from C a n a d a and t h e U n i t e d States began sampling various rock bodies for paleomagnetism in order to test such ideas. T h e s e data eventually became the primary weapons in a war pitting t h e geophysicists, armed with their paleomagnetic information, against t h e m a n y geologists w h o believed that plate tectonic models requiring large-scale transport of rock bodies over distances as m u c h as several t h o u s a n d miles were n o t necessary to explain the complicated geology found in western N o r t h A m e r i c a . T h e opening shot was fired in 1971, w h e n Robert Tessier and Merl Beck of Western W a s h i n g t o n S t a t e University published paleomagnetic data from t h e volcanic rocks making up M t . Stuart, a forbiddingly high peak in the N o r t h Cascades of W a s h i n g t o n S t a t e . C o m p a r e d with t h e largest of the Cascade m o u n t a i n s , such as M t . Rainier, or t h e nearby M t . Baker (which is still an active and exceedingly dangerous v o l c a n o ) , M t . Stuart is far more ancient, and it is "extinct." It has b e e n dated repeatedly, using sophisticated radiometric dating techniques, and all measures yield a Middle Cretaceous age of about 100 million years ago. T h e dispute about Mt. Stuart is n o t about its age but about where it was formed. T h e pioneering work hy Tessier and Beck resulted in a startling discovery: T h e y found t h a t Mt. Stuart was made up of rocks seemingly solidified at a latitude far to t h e south of its present position. If t h e paleomagnetic results were correct, t h e n the gurgling, bubbling, m o l t e n magma t h a t 100 million

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years ago solidified into what is n o w M t . Stuart did so somewhere off what is n o w S o u t h e r n California or Mexico. T h i s discovery shook the geological establishment to its core. S o o n afterward, o t h e r paleomagnetic findings suggested t h a t n o t just Mt. Stuart, but also o t h e r pieces of n o r t h w e s t e r n W a s h i n g t o n and southern British C o l u m b i a , journied from lower latitudes. Each of these rock bodies had to h a v e traveled between 2,000 and 3000 kilometers from the south. But here was more t h a n simple transport. T h e rock bodies were also rotated as

A) Morphogeological belts of Western Canada.

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much as 70 degrees—as t h o u g h a giant had grabbed t h e land and twisted it to the right. But was the paleomagnetists' interpretation correct? C o u l d t h e various volcanic rock bodies t h a t they e x a m i n e d not h a v e b e e n transported and yet have yielded such results? "Yes!" answered many geologists. Exactly these results would be expected if t h e various sampled rocks had b e e n tilted, rather t h a n transported.

B) Travel paths of various regions in Western North America relative to the craton (stable continental regions).

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It is m u c h easier to tilt a rock t h a n to transport it. Tilting takes place all the time: just look at any range of m o u n t a i n s and you will find rocks in every conceivable o r i e n t a t i o n , including turned upside down. T h e paleomagnetic interpretations relied on t h e ability to recognize original horizontally of the sampled rocks. T h i s was a key argument leveled by critics of paleomagnetic studies: T h e rocks sampled were n o t horizontal, and therefore t h e results wete spurious. T h u s t h e controversy started, pitting "drifters," or those w h o believed t h a t t h e various t e c t o n i c pieces n o w making up t h e Western Cordillera had assembled by c o n t i n e n t a l drift, against "fixists," w h o believed t h a t no such assemblage of exotic terranes h a d t a k e n place. T h e fixists did not doubt the validity of c o n t i n e n t a l drift; they just believed t h a t many c o n t i n e n t a l drift theories as applied to t h e western U n i t e d States and C a n a d a were simply figm e n t s of overwrought geophysical imaginations. Besides, argued the fixists, M t . Stuart a n d t h e N o r t h Cascades are n o t located on the coast but are miles inland. If they h a d b e e n transported, t h e n surely all rocks to the west of t h e m had to h a v e b e e n transported as well, and there was no apparent evidence of that. T h e n , in 1977, a study defining and identifying t h e greatest suspect terrane of all was published, and this significantly changed the debate.

A prime s u s p e c t T h e definition of the giant exotic terrane k n o w n called Wrangellia (after the Wrangell m o u n t a i n s of Alaska) was for several reasons a watershed event in plate t e c t o n i c study. First, t h e study was published by three senior and highly respected geologists employed by t h e U n i t e d States Geologic Survey: David Jones, N o r m Silberling, and J o h n Hillhouse. Second, until t h a t time most exotic terranes were hypothesized to be small land masses—island-sized at best. T h e Wrangellia Terrane as first envisioned was enormous: a relatively t h i n strip of land r u n n i n g n o r t h and south for many h u n d r e d s of kilometers. Finally, t h e m e a n s used to identify this a n c i e n t land mass and its drift history provided a methodological example fot most subsequent examinations of 94

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exotic terranes. In the Wrangellia paper, b o t h geological evidence and paleomagnetic evidence were used, rather t h a n only o n e or t h e other. T h e Wrangellia terrane was defined in terms of geological criteria. It is composed of Triassic-aged basalt t h a t appears to h a v e b e e n formed deep under t h e sea. More t h a n 200 million years ago, e n o r m o u s outpourings of basalt quite similar in texture and composition to those making up t h e Hawaiian Islands erupted from great submarine fissures. T h i s basalt c o n t i n ued to burp out for many millions of years a n d eventually accumulated into a mass of hardened lava many thousands of feet thick. Finally, in late Triassic

Present distribution of Wrangellia terrane.

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time, t h e fissure closed; no new lava emerged. By this time t h e lava had formed into a long, linear land mass. Limestone hegan to accumulate after the volcanic eruptions ceased, and t h e underwater e n v i r o n m e n t s where these limestone deposits formed were colonized hy early Mesozoic creatutes, including corals and many species of a m m o n i t e s . Wrangellia was enormously long. It e x t e n d e d from Vancouver Island as far as n o r t h Alaska. It may h a v e b e e n e v e n longet: Isolated scraps of rock in t h e Hell's C a n y o n region of O r e g o n and Idaho show the same telltale seq u e n c e of rocks used in t h e identification of Wrangellia. Both paleontologists and paleomagnetists found t h a t Wrangellia was e v e n more far-traveled t h a n Mt. Stuart. T h e origin of the Wrangellia basalt was somewhere in t h e southern h e m i s p h e r e . T h e e n t i t e rock body had t h e n b e e n carried n o r t h w a r d by c o n t i n e n t a l drift, eventually to crash into, and fuse o n t o , t h e western coast of N o r t h A m e r i c a . W h e n did this titanic collision take place? In t h e early 1980s, paleomagnetists made extensive studies of Eocene-aged rocks at o n e site near Mt. Stuart and at a n o t h e r to t h e east of Vancouver Island. In b o t h regions, a great thickness of 50-million-year-old sandstone accumulated in basins near a m o u n t a i n o u s region of high relief. T h e s e sedimentary rocks c o n t a i n palms and o t h e r fossilized tropical plants, w h i c h suggests t h a t they too may have c o m e from more southetly regions. But t h e world of t h e Eocene appears to h a v e b e e n warmer and wetter t h a n t h a t of today—a place where tropical forests could h a v e existed e v e n at t h e latitude of what are now W a s h i n g t o n S t a t e and s o u t h e r n British C o l u m b i a . T h e paleomagnetic results confirmed this; n o n e of t h e Eocene-aged sandstone showed any evidence of drift. These studies place an upper time limit on t h e collisions of Wrangellia with N o r t h America: 50 million years ago. T h e idea t h a t this long, t h i n terrane had smacked into N o r t h America sometime in t h e late Mesozoic had just filtered down into textbooks when, in the mid 1980s, t h e whole c o n c e p t of Wrangellia changed. It began to grow in t h e eyes of some geophysicists. T h e prime m o v e r in this was Ted Irving of t h e Geological Survey of C a n a d a . Irving, a paleomagnetist, was stationed in Victoria and thus h a d ready access to British C o l u m b i a rocks. 96

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His studies began to c o n v i n c e h i m t h a t far more t h a n Vancouver Island and the Q u e e n C h a r l o t t e Islands ( t h e two prime pieces of t h e Wrangellia terrane in C a n a d a ) had moved up t h e coast. Irving began to wonder if n o t just this terrane, but s o m e t h i n g larger, had traveled up. S o o n Wrangellia received a new n a m e : the Insular Superterrane. It n o w encompassed n o t only Vancouver and the Q u e e n C h a r l o t t e s hut all of t h e coastal m o u n t a i n s of British C o lumbia as well. T h e vision n o w was of a huge h u n k of real e s t a t e — a subcontinent something like India in size, but longer and skinnier—smashing and accreting o n t o the coastline. Irving coined a new n a m e for this superterrane, calling it Baja British C o l u m b i a after Baja California, t h e latitude from which he believed it had c o m e , so long ago. T h e entire idea b e c a m e k n o w n as the Baja British Columbia hypothesis. Irving was no stranger to controversy. As a graduate student at C a m bridge University in t h e 1950s, he had b e e n o n e of t h e first of his generation to embrace paleomagnetics as a tool for studying past c o n t i n e n t a l positions. 1 lis studies, which were conducted j u s t before the emergence of c o n t i n e n t a l drift and plate tectonics as an accepted theory, cleatly showed t h a t either t h e c o n t i n e n t s were drifting or t h e poles of t h e a n c i e n t e a r t h had had t e n d e n c y to wander. Irving refused to accept t h e latter possibility and thus embraced the idea t h a t the c o n t i n e n t s had drifted. Unfortunately, C a m b r i d g e U n i v e r sity was not so o p e n - m i n d e d and refused to award h i m his hard-earned P h D . Irving was forced to start again at a n o t h e r university. O n l y m u c h later did a very sheepish Cambridge award Irving an honorary P h D . As the 1980s progressed, e v e n this e n o r m o u s land mass grew larger in the c o n c e p t i o n of t h e geophysicists. Now, n o t only t h e coastal m o u n t a i n s and Vancouver Island in British C o l u m b i a ( t h e Insular Superterrane) were thought to have drifted; the I n t e r m o n t a n e r e g i o n — t h e entire suite of gigantic mountains that make up most of British C o l u m b i a — w a s added into t h e mix as well. By t h e late 1980s, geologists from the University of W a s h i n g t o n (Darrel C o w a n and his students Paul Umhoefer, Mark Brandon, and J o h n Garver) had refined this model. T h e y put it on a fat more rigorous footing by conducting kinematic studies showing how t h e plate m o v e m e n t could h a v e produced this event. 97

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According to all studies, t h e southern limit of Baja British Columbia is found in t h e S a n J u a n Islands of n o r t h e r n W a s h i n g t o n state. In fact, Sucia Island may mark o n e bit of this southern boundary. T h e rocks making up the fossiliferous portions of Sucia, as well as other parts of the U p p e r Cretaceous N a n a i m o G r o u p of t h e Vancouver Island region, suddenly became critical elements if this idea of a drifting s u b c o n t i n e n t smashing into N o r t h America was to be tested. M t . Stuart, 100 million years old, seemingly obtained its magnetic signal somewhere in t h e latitude of Mexico. T h e Eocene rocks of n o r t h e r n W a s h i n g t o n seem to h a v e originated at a latitude similar to that of their present location. T h e rocks of intermediate age, t h e fossiliferous rocks of t h e N a n a i m o G r o u p — i n c l u d i n g Sucia Island—would seem to hold the key. Two teams of A m e r i c a n and C a n a d i a n scientists, led by Merle Beck and Ted Irving, quickly began to sample the rocks of the Vancouver Island region. Here, surely, would be t h e key to unraveling—confirming or refuting—the mystery of Baja British C o l u m b i a . Did it exist at all? H o w m u c h drift took place? To their dismay, they found only nonsensical results. T h e problem, again, was reheating. M a g n e t i c crystals locked in rocks provide t h e compasses t h a t reveal a n c i e n t pole positions. However, if t h e rocks in w h i c h they sit are reheated, t h e force lines of t h e m a g n e t i c field c h a n g e o r i e n t a t i o n at t h e time of reh e a t i n g . All previous information is erased, or overprinted. S o m e t i m e in t h e early Tertiary Period, p e r h a p s 50 million years ago, large portions of V a n c o u v e r Island were r e h e a t e d . T h e cause of this h e a t i n g is poorly understood. Perhaps t h e island ran over a h o t spot, or p e r h a p s regional volcanism simply h e a t e d larger parts of t h e region. T h e result, in any case, was to scramble t h e precious m a g n e t i c information locked in t h e rocks— information t h a t could h a v e b e e n t h e decisive test of drift history. Because of this, it was soon widely t h o u g h t t h a t no reliable m a g n e t i c signal would ever be recovered from t h e V a n c o u v e r Island region. T h e p a l e o m a g n e t i c results from my drilling on H o r n b y Island in 1986 only seemed to confirm this view. But as so often h a p p e n s in science, a c h a n c e e v e n t would alter this perception.

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Baja C a l i f o r n i a Late N o v e m b e r in Seattle is a bitter time. S u m m e r is long gone, only a distant memory. W i t h N o v e m b e r c o m e t h e Pacific gales, bringing u n r e l e n t i n g rainfall. Days pass with no glimpse of t h e sun, and in t h e high latitude of the Pacific N o r t h w e s t t h e N o v e m b e r days are short. Darkness comes early, and the spirit is challenged. No tourists visit Seattle in N o v e m b e r , and t h e n u m ber of suicides skyrockets. It is a great m o n t h to escape southward, to sunnier climes and a m m o n i t e - r i c h rocks. No wonder N o v e m b e r has b e e n c h o s e n as the prime time to study geology in Baja California. T h e r e is no easy way to get to Baja. My o w n route always passes t h r o u g h Pasadena, h o m e to the California Institute of Technology. On my first-ever trip to this fabled institution, my plane landed in Burbank in t h e dark. T h e n I made my way to Pasadena by shuttle, finally to be deposited at t h e front door of an impressive stucco building: the A t h e n a e u m , Cal Tech's faculty club. Faculty clubs are normally somewhat cheesy affairs tucked away in some forgotten corner of a university campus and frequented by the poorly dressed army of university faculty. Yet this place was elegant, old-money Californian. T h e upper stories of the building formed a comfortable hotel. Downstairs was a huge living room, walls covered with portraits that constituted a veritable Who's Who of A m e r i c a n science in this century. Rich, thick carpets leading to a large dining room muted murmurings from well-dressed patrons (most of whom, I later learned, were not faculty members but wealthy Californians willing to shell out large membership fees to rub elbows with the distinguished faculty). Dressed as I was in field gear and hiking boots, I looked like a m a n in a Hallowe'en costume, and t h e other patrons looked at me as if I were a Martian. I had traveled to Cal Tech as the fitst leg of an expedition to Cretaceousaged exposures found along the western coastline of Baja California. My host for this trip was a m a n I knew by r e p u t a t i o n but had never met, t h e paleomagnetist Dr. Joseph Kirschvink. After settling i n t o my room, I set out to find Kirschvink. I was told t h a t he was currently speaking in o n e of the largest of the university's lecture halls. It seemed odd to m e : past 8 PM and

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still teaching. 1 made may way across t h e gardens and walkways of the Cal Tech campus to t h e lecture hall in question. I c a m e to t h e appointed door, entered, and saw a sea of humanity, perhaps 300 people. It was also clear that those packing t h e lectute hall were n o t students; they were too well dressed, too old. I found a seat and focused on t h e speaker: a somewhat diminutive m a n from a distance, a rather h i g h speaking v o i c e — a n d the most extraordinary subject. Kirschvink was telling his audience t h a t there is a sixth h u m a n sense in addition to t h e well-known five. All of us, he said, h a v e an innate sense of direction, produced hy small crystals of m a g n e t i t e found within virtually every brain cell, a discovery m a d e largely by Kirschvink himself. This was my i n t r o d u c t i o n to my new scientific partner. I had been invited to join a very famous field trip. Every year since the early 1980s, Kirschvink has t a k e n several loads of students (and the occasional lucky outsider such as myself) to Baja California to study the local geology. I had heard about this trip from various colleagues for several years and hy sheer good fortune had managed to get myself invited, not knowing at t h e time t h a t our road to Baja would eventually take us back to Vancouver Island. We assembled the n e x t m o r n i n g to load t h e vans, bought huge amounts of groceries, a n d set out. T h e C a l T e c h Baja trips entail endless driving. T h r e e hours from Pasadena to t h e border at Tijuana, t h e n a n o t h e r two or so to Ensenada, and t h e n south on Highway 1. An hour south of Ensenada we turned west into t h e hills on a track t h a t could only euphemistically be called a road, over rugged countryside and washboards, the entire van now filled with dust. We finally arrived, in early evening, at our c a m p site. Tents were pitched in t h e dark u n d e r starry skies, but a h o w l i n g wind from t h e n e a t b y sea drove us into sleeping bags early. M o r n i n g , however, brought epiphany. Emerging from my REI special 1 found t h a t our tents sat atop a rugged seacoast cliff, near a tall white lighthouse. A dirt track led d o w n to t h e sea, where green shale m a d e up low coastal cliffs stretching to the horizon. 1 descended to t h e b e a c h and its rocky cliffs, crossing the intertidal rocks gloaming under a retreating tide. I watched pelicans wheel overhead. I noted the 100

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remains of rock lobsters and tropical snail shells, feeling the glow of salty air and a warm lapping sea—in a geological setting made up of rocks and fossils so familiar as to be bizarre in this near-tropical c o n t e x t . T h e rocks were old friends from my earnest boyhood days on Orcas and Sucia Islands. A n d it wasn't just the rocks. Far more telling were t h e fossils, old ftiends too, ammonites and snails familiar from the Vancouver Island region, yet sitting here e n t o m b e d in this gray green matrix on a Mexican n o t C a n a d i a n coast, a n n o u n c i n g their names with a Spanish accent: Baculites, Hoplitoplacenticeras, Desmophyllites, Inoceramus.

Perhaps it was c o i n c i d e n c e t h a t these

rocks and those of Sucia and Vancouver Islands shared fossils as well as lithology. But perhaps n o t . Joe Kirschvink h a d studied t h e paleomagnetic signals of these rocks over the years to ascertain their a n c i e n t latitude. His questions were thus fundamentally different from the research questions I h a d b e e n e x a m i n i n g via paleomagnetics. Joe was interested in a n c i e n t c o n t i n e n t a l positions; my work, up to this point, had been c o n c e r n e d only with time as calibrated by the geomagnetic polarity time s c a l e — t h e record of geomagnetic reversals. Joe's work on this beach d e m o n s t r a t e d t h a t t h e paleolatitude of Baja California some 75 to 80 million years ago was nearly t h e same as it is now: between 20 and 25 degrees n o r t h latitude. But what of Vancouver Island? Was the Baja British C o l u m b i a hypothesis correct? We spent several days touring various outcrops along t h e coast, spending little time on any given outcrop. N i g h t s were filled with food, C o r o n a , nips of Tequila, and m u c h conversation. On this trip, Joe and I launched a friendship and a scientific collaboration as well. N e i t h e t of us m u c h liked the possibility t h a t the Vancouver Island rocks were completely reheated, and we discussed areas t h a t had not yet been sampled, regions t h a t might c o n t a i n an original, Cretaceous-aged paleomagnetic record t h a t could give reliable paleolatitude for t h e Vancouver Island region at a time w h e n dinosaurs still ruled the earth. It was on this first Baja trip t h a t we began to make plans to m o u n t yet a n o t h e r assault on the paleomagnetics of V a n c o u v e t Island, this time armed with better sampling t e c h n i q u e s a n d a far better paleomagnetic laboratory to analyze t h e cores. It took several years and a grant from t h e 101

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N a t i o n a l Science F o u n d a t i o n to bring these plans to fruition. On t h e C a n a dian expedition, it was Joe's turn to fly.

Baja B r i t i s h C o l u m b i a We arrived on H o r n b y Island in early summer of 1995: Joe Kirschvink, Jose H u r t a d o (a student assistant from C a l T e c h ) , and me. We walked the beach at t h e lowest of tides, t h e sun glancing off an occasional a m m o n i t e shell still held tightly in t h e sediment. T h e a m m o n i t e s , it turned out, gave us our best h o p e of finally getting a real paleomagnetic position of these a n c i e n t sediments. T h e shells and t h e shapes of t h e fossils were our clue. Temperature is the key to paleomagnetic analyses; if t h e sediments were heated too much, they lost their magnetic signal. But our a m m o n i t e shells also reacted to high temperature: T h e i r pearly shells retained luster only in the absence of heat. A n y regional h e a t i n g would recrystallize these shells to a dull tan or even black. Because of t h e pristine n a t u r e of t h e a m m o n i t e s from Hornby and from a few o t h e r islands of t h e Vancouver Island region, we were confident that a reliable paleomagnetic signal could be found. T h e key to success this time on H o r n b y would be avoiding rocks t h a t appeared to be oxidized in any way or did n o t h a v e a fresh surface. Joe's solution was to excavate all surface rock deeply away before drilling, to ensure fresh rock. For several days t h e three of us worked in exquisite weather, camping nearby and sampling island cuisine after work. W i t h more t h a n 60 cores obtained, we moved n o r t h to o n e of t h e largest and most obscure of t h e islands in this region, a place called Texada Island. Here too we sampled t h e strata, this time with m u c h more difficulty, for the timber companies had devastated this island. W h e r e a s on H o r n b y t h e fossiliferous rock is exposed on a seacoast, on Texada t h e sampling locality was an overgrown creek t h a t years ago h a d b e e n clear-cut. T h e timber c o m p a n y t h a t did the c u t t i n g on this creek never cleaned up t h e snags, and t h e creek was an overgrown mass of felled dead wood and colonizing brambles. O u r prime locality could be reached only by crawling half a mile over t h e snags carrying our heavy gear, and it was relief w h e n we finally finished this work without a n y o n e breaking 102

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an ankle or worse. T h e field sampling was finished. T h e n e x t phase occurred at Cal Tech, deep in t h e basement of t h e geology building, where Joe maintains his paleomagnetics lab. A m a g n e t o m e t e r is an odd device cooled by liquid nitrogen. T h e small cores we had extracted from the rocks of H o r n b y and Texada Islands were sent downward into the freezing heart of this m a c h i n e like H a n Solo being turned into a wall h a n g i n g at t h e conclusion of The Empire Strikes Back. In go the cores, out come t h e cores, and n u m b e r s flash across a digital readout screen. Each core is repeatedly analyzed, and t h e n begins t h e long process of removing spurious magnetic overprints. T h e cores are h e a t e d in i n c r e m e n t a l steps: first 100°C, t h e n 150°C, and on up in 5 0 ° C increments. After each heating, which takes about an hour in t h e oven, t h e core is analyzed again. Slowly the obscuring overprints of h e a t are stripped out of t h e cores; gradually an original signal comes into view; and if all goes well, after many hours, each core provides o n e d a t u m point. Jose H u t t a d o had d o n e m u c h of this work for the Hornby and Texada cores, and I h a d c o m e to see t h e final results. Joe had taken t h e data and analyzed t h e m using a statistical m e t h o d he had devised more t h a n a decade earlier. On page after page of p r i n t o u t he now held t h e end of a long journey: t h e m e a n latitude of b o t h H o r n b y and Texada Islands was 25 degrees n o r t h latitude at t h e time w h e n their rocks were deposited, late in t h e A g e of Dinosaurs, about 80 to 70 million years ago. Both islands show t h e same latitude as Baja California today. T h e r e are great m o m e n t s in life. For me, this was o n e . I wrote an account and submitted it in all our names to Science magazine. T h e n we waited several anxious m o n t h s for t h e reviews to c o m e in. Science is the most difficult of all scientific journals to be accepted in; its editors require that t h e scientific problem being e x a m i n e d be of general interest to all scientists and they require t h a t two external referees give t h e manuscript a ringing endorsement. On the day t h e letter arrived, I ripped o p e n t h e envelope a n n o u n c i n g the official decision. Despair! O n e of t h e reviewers had flatly dismissed our results as "spurious." He decreed t h a t we h a d simply measured effects of a disputed p h e n o m e n o n called "inclination shallowing." It was clear where this review had c o m e from. Science had sent our manuscript 103

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to die-hard critics of this particular terrane drift—two m e n w h o do n o t accept t h e validity of t h e Baja British C o l u m b i a hypothesis. I n c l i n a t i o n shallowing is a p h e n o m e n o n w h e r e i n c o m p a c t i o n of sedi m e n t , caused hy t h e slow but inexorable a c c u m u l a t i o n of sedimentary beds o n e a t o p a n o t h e r , e v e n t u a l l y flattens underlying s e d i m e n t to the p o i n t w h e r e t h e m a g n e t i c signal "shallows," or gives e v i d e n c e of a lower latitude t h a n was originally present in a bed. For e x a m p l e , some sedimentary bed m i g h t h a v e b e e n deposited in latitude 45 n o r t h . However, the gradual squashing of this s e d i m e n t over t i m e may slightly flatten out the small m a g n e t i t e grains such t h a t t h e p a l e o m a g n e t i c signal measured might be 34 or 35 degrees. T h e s e two reviewers h a d dismissed every Mesozoic pal e o m a g n e t i c of tropical latitudes in n o w - n o r t h e r l y localities as either due to i n c l i n a t i o n shallowing or c o m i n g from studies w h e r e t h e original horizontal a t t i t u d e of t h e rocks could n o t be ascertained. O u r paper was rejected. If I was ctestfallen, Joe was outraged. O u r study was not contaminated by c o m p a c t i o n shallowing, he a n n o u n c e d to me over t h e p h o n e soon after our rejection, for a simple reason: T h e a m m o n i t e s , so a b u n d a n t in the sediments from H o r n b y and Texada, were n o t compressed. If c o m p a c t i o n shallowing were taking place, it would affect n o t only t h e magnetite hut t h e fossils as well: T h e fossils would he flattened. Clearly they were not, so inclination shallowing could n o t h a v e t a k e n place. We c o m m u n i c a t e d this to t h e editors in an appeal, and after more reviews t h e paper was accepted. Published on S e p t e m b e r 12, 1997, it ptesented a data set t h a t gave more credibility to those w h o m a i n t a i n that the "suspect terrane" k n o w n as Baja British C o l u m b i a is less suspect t h a n most. W h o — o r w h a t — w a s watching, so many millions of years ago, w h e n t h e entire block of what is now British C o l u m b i a crashed into N o r t h A m e r i c a to be welded in place? M a g n e t o m e t e r s ate the time m a c h i n e s that h a v e revealed to us this surprising e v e n t in earth history, w h e n a n c i e n t Mexico cast off its moorings a n d sailed n o r t h . C a n a d a is a far richer place as a result. But will t h e M e x i c a n g o v e r n m e n t , so keen on repatriation, d e m a n d its territory hack? 104

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Sedimentary rocks continuously c h a n g e in a p p e a r a n c e as we follow t h e m either up or down into time. T h e stacked layers b e c o m e more fine- or coarse-grained, and they c h a n g e from o n e type of sedimentary rock to a n other. For rocks deposited b e n e a t h t h e sea, it seems t h a t t h e d e p t h of deposition is t h e prime factor in d i c t a t i n g these changes. W a t e r d e p t h a n d changes of water d e p t h ( w h i c h in m a r i n e e n v i r o n m e n t s is termed sea level change) h a v e played a large part in d e t e r m i n i n g w h a t type of sedimentary rock is deposited in any given u n d e r w a t e r l o c a l e — a n d thus h a v e played a major role in fashioning t h e a p p e a r a n c e of our planet's sedimentary rock cover. But sea level c h a n g e has b e e n blamed for more t h a n simply influencing the fate of a n c i e n t sand grains ( a n d thus c o m p l i c a t i n g geologists' lives, 105

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as they grapple with describing sedimentary rocks). It has also been implicated in t h e gteatest mass murders to h a v e occurred on this planet. Sea level c h a n g e is a prime suspect in t h e periods of mass d e a t h , called mass extinctions, t h a t shaped out planet's hiota. T h e way geologists h a v e deciphered sea level c h a n g e is thus a p o t e n t type of t i m e m a c h i n e for planetary detectives on t h e global h o m i c i d e detail.

Trekking through time T h e study of sea level c h a n g e is part of t h e discipline of sedimentology, the study of the way sedimentary or layered rocks form. T h i s b r a n c h of geology gives us t h e tools necessary to reconstruct t h e geography of a n c i e n t lands. Sedimentary rocks can be seen forming today in a variety of e n v i r o n m e n t s on land and in water, such as in deserts, lakes, rivers, and oceans; and they surely did so in similar fashion in t h e past. T h i s belief forms the core of the Principle of Uniformitarianism, w h i c h holds t h a t t h e present is the key to t h e past. For instance, t h e way in w h i c h sand grains accumulate into sedim e n t a t y beds on a m o d e r n - d a y beach or riverbed is probably the way such processes occurred on a n c i e n t beaches or riverbeds. Time may change, but the laws of physics, w h i c h control t h e accumulation of sedimentary rocks, do n o t . T h e principle of uniformitarianism is most powerfully used in the field of sedimentology, where it enables us to reconstruct past e n v i r o n m e n t s . In like m a n n e r , we c a n often r e c o n s t t u c t a n d d e d u c e t h e "life habits" of a n c i e n t organisms by studying h o w m o d e r n forms of similar species aggregate and live. Each sedimentary e n v i r o n m e n t , be it a riverbed or desert floor, produces a specific type of sedimentary rock, for t h e physical forces operating in each particular e n v i r o n m e n t frequently dictate how t h e resulting assemblage of sedimentary rocks will look. Deserts, for instance, accumulate sandstone amid wind-blown sand dunes, which more often t h a n n o t leave a tecord of their existence in t h e rock itself, in the fotm of switls and irregularities in bedding k n o w n as cross beds. A n y such marks in sedimentaty rocks are k n o w n as sedimentary structures, and these often provide the most specific 106

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clues to ancient sedimentary e n v i r o n m e n t s . T h e sedimentary rocks forming in a deep ocean look quite different from desert deposits, because they h a v e accumulated in m u c h quieter, lower-energy e n v i r o n m e n t s and consequently show different grain sizes and sedimentary structure t h a n do desert deposits. Any fossil types present are also i m p o r t a n t clues to reconstructing t h e environments in which a particular sedimentary rock accumulates. Organisms are restricted to very specific types of e n v i r o n m e n t s and, w h e n preserved as fossils, are among t h e best of all sources of information about what t h e "place" was like where a given assemblage of sedimentary rocks accumulated. W h e n all of these types of evidence are considered together, they can yield a detailed understanding of an a n c i e n t e n v i r o n m e n t . T h e sedimentary rocks on Sucia Island, for example, can be analyzed in this way, by c o m b i n i n g t h e evidence gleaned from grain size, sedimentary structures, and t h e enclosed fossils. To make such an analysis, we need to "walk the section," beginning amid t h e lowest (and h e n c e oldest) of t h e island's sedimentary rocks and finishing amid t h e highest, or youngest. If Sucia's sediments retained their original horizontality, we would need a huge stepladder to complete such a task. But Sucia's rocks h a v e b e e n c o n t o r t e d in such a way as to make our job m u c h easier. T h e sedimentary rocks of Sucia Island h a v e b e e n subjected to enormous compressional forces t h a t h a v e deformed t h e region such t h a t t h e island, as seen from the air, n o w describes a series of gigantic nested horseshoes tens of miles across. We can see h o w this occurred by "performing" t h e following "thought e x p e r i m e n t . " Imagine t h a t t h e a n c i e n t sedimentary beds of Sucia Island are represented by a t e l e p h o n e book, e a c h page representing one layer of strata. T h e book lying on a flat surface represents the strata of Sucia prior to deformation, each page horizontal and parallel to every other. However, the Sucia strata were n o t to be left in such peace. Imagine t h a t the two sides of the book are squeezed, causing it to assume t h e shape of a half tube, with the spine of t h e book and t h e pages on t h e o p e n side p o i n t i n g up. If we now take this deformed book and jam it into t h e surface it sits on at a 60-degree angle, we h a v e roughly reduplicated t h e forces t h a t the Sucia Island strata h a v e undergone. T h e resulting curvature is sure evidence t h a t the 107

Part of the sedimentary section on the south coast of Sucia Island. The lowest (oldest) beds are at the bottom of the photo, the highest (youngest) at the top.

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once-flat-lying sedimentary rocks h a v e b e e n involved in a regional compressional episode of t h e sort t h a t c a n produce m o u n t a i n s . Millions of yeats ago, the flat layer cake of strata making up Sucia was slowly pushed against an unyielding wall of m o u n t a i n s to t h e east. T h e layers first b e n t , t h e n buckled and broke. All such effects are manifest on Sucia as tilted strata and faults. T h e originally flat layers dip at an angle of nearly 60 degrees, making t h e complete book of strata t h a t is now Sucia Island easy for us to read. Simply by strolling along a beach of t h e island, we c a n walk t h r o u g h t i m e — t h r o u g h the entire pile of sedimentary beds. T h e oldest sedimentary rocks t h a t make up Sucia Island are located on its southern margin. Let us start out there on a sparkling May m o r n i n g , warm sun prickling our still wintry skin, and walk t h e intertidal, o n e eye w a t c h i n g our step on t h e beach strewn with boulders a n d driftwood, t h e o t h e r watching the ever-changing cliffside rocks. We will need a low tide, because t h e t e are several landslides that would otherwise b a n our way along t h e p a t h we must follow on Sucia's s o u t h e r n coast. T h e most a n c i e n t strata on t h e island are conglomerates, t h e type of rock made up of larger rock particles, such as gravel and cobbles. T h e s e conglomerates on Sucia are a chaotic and jumbled pile ot rounded rocks, a few as large as a bowling ball. In some areas t h e conglomerates c o n t a i n beautiful white quartz; in o t h e r places a more variegated rock assemblage is visible. T h e various rocks in this basal c o n g l o m e r a t e are sure clues to t h e n a t u r e of the land area that was nearby w h e n these rocks were deposited, for they are so large t h a t they could n o t h a v e b e e n transported far from their original m o u n t a i n sources. We can surmise t h a t these cobbles were brought to t h e edge of a sea by rivers tumbling d o w n from nearby coastal m o u n t a i n s ; in this conglomerate we see bits and pieces of these a n c i e n t m o u n t a i n s . T h e y give us our first glimpse of a n c i e n t Sucia Island—it was near m o u n t a i n s . T h e aggregate thickness of Sucia's basal conglomerate is perhaps 100 feet, but because the beds are tilted on their side at a 60-degree angle, we rapidly pass through this thickness of rock as we walk along. T h e rocks are exposed b o t h as a low cliff lining the beach and as a b e n c h along t h e beach

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itself. T h e r e is very little bedding or any o t h e r type of sedimentary structure visible in t h e conglomerates. T h e y make up an imposing coastline. As we c o n t i n u e our walk, we eventually c o m e to a transition, where the conglomerate is overlain by a n o t h e r sediment type, o n e d o m i n a t e d by sandstone. T h i s gradual transition is best seen in t h e rocky sides of the cliffs lining the beach. O v e r several meters of thickness, the rocks in this conglomerate grow finer, c h a n g i n g from cobble, to gravel, to very coarse sand-sized material. T h i s transition in grain size is o n e bit of evidence t h a t t h e a n c i e n t environm e n t of deposition t h a t created this part of our stratigraphic section was rapidly changing. W h e n e n v i r o n m e n t s remain the same, so do the rocks deposited in t h e m . A n y c h a n g e in rock type tells us t h a t t h e environments, w h i c h control rock type, must themselves h a v e s o m e h o w changed. In these oldest of Sucia strata, we find only small shards of fossil shells. T h e y are so fragmented a n d abraded t h a t they c a n ' t be assigned to any genus or species. N e v e r t h e l e s s , they c a n still tell us s o m e t h i n g about t h e a n c i e n t e n v i r o n m e n t s where these coarse, basal strata were deposited. T h e fact t h a t t h e r e are fossils at all in t h e c o n g l o m e r a t e s and basal sands t o n e , a n d t h e fact t h a t they are all fragmented, are i m p o r t a n t clues. T h e y tell us t h a t t h e basal Sucia strata a c c u m u l a t e d in a high-energy environm e n t at t h e edge of t h e sea a n d t h a t these fossils were transported by currents a n d b r o k e n by heavy wave a c t i o n . T h i s biological e v i d e n c e is consist e n t w i t h t h e clues given by t h e n a t u r e of t h e sediments themselves, for the gravel and coarse s a n d s t o n e show u n m i s t a k a b l e signs of water m o v e m e n t . T h e pebbles of t h e c o n g l o m e r a t e s are all stacked in a rough order—a process called i m b r i c a t i o n t h a t occurs only w h e n small rocks are deposited in m o v i n g water. T h e s a n d s t o n e t o o gives e v i d e n c e of h a v i n g been deposited in m o v i n g water; it shows t h e sedimentary structures called cross beds, t h e fossil remains of a n c i e n t sand dunes or ripples, b o t h of which can form only in m o v i n g water. From this e v i d e n c e , we thus arrive at a convincing picture of a seashore w h e r e strong waves act on gravel and sand. T h e fossil material was probably brought in from deeper water by this wave action.

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As we resume our stroll along t h e a n c i e n t sedimentary beds t h a t now make up the Sucia Island s h o r e — a n d thus m o v e ahead in t i m e — w e begin to see marked changes in the fossil evidence. We are n o w well into t h e sandstone beds. T h e fossils here are still fragmented, but n o w t h e r e are far more of t h e m t h a n below, in t h e conglomerates, and h e r e in t h e sandstone they ate c o n c e n t r a t e d in distinct beds. T h e s e beds are packed with t h e remains of small snail and clam shells. T h e clam fossils look a lot like clams found in today's shallow seas. T h e layers they sit in look m u c h like sedimentary beds sculpted today during large storms, and we can assume t h a t these a n c i e n t beds were formed in similar fashion, during large storms striking the a n c i e n t seashore that was Sucia Island, more t h a n 75 million years ago. As we c o n t i n u e our trek, we observe t h a t t h e coarse sandstone begins to change subtly in appearance. T h e r e are fewer of the shell layers and more fossils occurring singly or in small groups. T h e fossils appear better preserved as well, and some are much larger t h a n any we h a v e seen before. T h e majority of fossils are clam shells, but there are many snails as well. Two types of fossils ate most noticeable because of their large size and a b u n d a n c e : long prism-shaped clams, some half a foot long, and o t h e r clams with a very knobby and sharpridged appearance. T h e first of these is a clam k n o w n as Pinna, which can be found in abundance today in many tropical regions of t h e world. T h e second is Trigonia, found today only in Australia. T h e presence of these two fossils is another type of clue: It alerts us to the possibility that the a n c i e n t Sucia envir o n m e n t was far more tropical t h a n now, t h a t these fossil lived in shallow seas of the type we find in the coral reef latitudes. W h e n we e x a m i n e the snail shells hete on Sucia, we arrive at a similat conclusion. Most of t h e m are made up of species that today are found only in shallow, warm, tropical seas. N o w we move faster t h r o u g h time, ever upward t h r o u g h this pile of stacked strata, and the sand gives way to a finer sediment. All vestiges of t h e shallows begin to disappear: No longer can we see any evidence of storm beds, no longer can we see t h e ripples t h a t waves might fotge. It is as if we are standing at the b o t t o m of an aquarium t h a t is slowly being filled, and the level of the sea rises above our heads.

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T h e fossils c h a n g e as well. T h e large n u m b e r of clam fossils, made u p — until n o w — o f many types quite familiar to us, b e c o m e d o m i n a t e d by larger, flat clams t h a t resemble oysters. T h e s e are t h e inoceramid clams, perhaps the most ubiquitous species of t h e Cretaceous Period and a form t h a t went completely e x t i n c t at t h e e n d of t h e Cretaceous. T h e y are found singly in the Sucia sediment and are often encased in concretions, the hard mud balls so characteristic of deeper-water deposits. A m m o n i t e s n o w appear for the first time—mostly t h e straight Baculites, but o t h e r species are found as well. Larger coiled varieties are found, some smooth-shelled, others o r n a m e n t e d with an astonishing array of ribs and knobs. H o w did these shells get here? A m m o n i t e s were swimmers like fish, and they used their astonishing, c h a m bered shells to m a i n t a i n buoyancy m u c h as a submarine does. T h e y must h a v e c o m p e t e d with fish as active predators. We can imagine the ammonites swimming above fine muddy b o t t o m s — b o t t o m s covered with worms and clams, crustaceans and urchins, b o t t o m s perhaps 100 feet deep or m o r e — a n d sinking d o w n o n t o these muddy b o t t o m after their d e a t h . We are n o w in a very fine sediment, a silty matrix with many concretions. We are also n e a r t h e end of our walk, for although more rock is present, we would h a v e to dive to see it. T h e strata on Sucia can be seen to continue underwater from t h e edge of t h e shore, but no observations can be made because of t h e profusion of m a r i n e life growing over these underwater deposits. We h a v e crossed a quarter-mile of beach and h a v e traversed more t h a n 600 aggregate feet of sedimentary beds. O n e message comes through loud and clear: T h e a n c i e n t e n v i r o n m e n t of Sucia Island saw an ever-rising level of t h e sea, a sea t h a t first lapped on a seashore and ended at a level far above a deep muddy b o t t o m . Did t h e sea rise, or did t h e land subside? A n d did this c h a n g e h a p p e n only here or all over t h e world at t h e same time? To answer these questions, we need to step back and e x a m i n e a larger area t h a n Sucia Island, and we need to look at a longer slice of time as well. T h e marine rocks on Sucia are but a small bit of t h e m u c h thicker pile of strata that make up t h e N a n a i m o G r o u p . Let's us look at t h e lithologies of this great pile of strata in t h e h o p e of extracting more information about the a n c i e n t envir o n m e n t of this place. 112

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Sea l e v e l c h a n g e and a n c i e n t e n v i r o n m e n t s Just across t h e international border from Sucia Island is an assemblage of islands big and small n a m e d the Gulf Islands. T h e y are almost entirely made up of the same sedimentary rock t h a t constitutes t h e n o r t h e r n tier of the S a n Juan Islands. ( T h e n a m e c h a n g e is purely a m a t t e r of nationalism, n o t geological history.) T h e seaway in w h i c h these islands n o w float was carved by the glaciers of the last 2.5 million years, w h i c h repeatedly slid d o w n t h r o u g h the regional bedrock to carve out this spectacular fjord-like real estate. But the actual creation of the rock that makes up these islands took place m u c h longer ago, near the end of the A g e of Dinosaurs, as we h a v e seen. If we take a boat tour through these islands, we can see the entire package of ancient sedimentary rock that makes up this assemblage, which is named the N a n a i m o G r o u p . It is really a group of formations, each formation being defined by a distinctive lithology of rock type. A b o u t eleven or twelve formations have been recognized, and their aggregate thickness would be more than 15,000 feet—3 miles of strata—if they were piled up in o n e place. T h e name N a n a i m o G r o u p comes from a large town on Vancouver Island where these rocks were first identified. T h e lowest strata of the N a n a i m o G r o u p are composed of gravel and sandstone quite coarse in nature, and our best guess is that they are about 85 million years old. T h e r e is a b u n d a n t fossil and lithological evidence that these basal N a n a i m o G r o u p strata were deposited in rivers or on land. Perhaps it was a river valley or perhaps a flood plain; whichever, these oldest deposits were certainly not laid down in the sea. But overlying these continental deposits, which themselves sit upon far older volcanic rock, is a dark shale that is indeed the remains of an a n c i e n t ocean bottom. T h e s e lowest marine rocks are called t h e Haslam Formation. T h e y are widely exposed over m u c h of Vancouver Island, as well as being found on members of b o t h t h e Gulf and San Juan Islands. T h e Haslam Formation is usually more t h a n 1000 feet thick and rich in fossils. T h e most a b u n d a n t of these fossils are small forms called inoceramid clams, a type n o w extinct. But also found in substantial numbers are a m m o n i t e s . At least twelve species occur, sporting t h e disc-like shells as well as curious, uncoiled ones. S o m e 11 ?

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look like candy canes, others are shaped like snails. S o m e are completely uncoiled, others only slightly so. T h i s rich diversity proclaims t h a t ammonites, e v e n this late in t h e i t history, wete wildly successful creatures. During the time t h a t t h e Haslam Formation was being deposited across m u c h of the Vancouver Island region, they proliferated. T h e presence of a m m o n i t e s in t h e Haslam Formation is a sure sign that these tocks were formed in t h e sea, n o t on land. T h e a m m o n i t e s tell us that t h e Haslam Formation can be approximately correlated to rocks in the Western Intetior t h a t c o n t a i n a m m o n i t e s and ash beds. T h o s e ash beds are radiometrically dated at over 80 million years in age. T h i s figure gives us a sense of t h e maximal age of these sediments on Vancouver Island. T h e Haslam Formation can be seen in river cuts and shorelines, and it is usually tilted as a result of regional land m o v e m e n t and m o u n t a i n building. As on Sucia, w h e n t h e formation is tilted, we can most easily measute its thickness and most easily observe t h e rocks t h a t succeed it. A n y package of sedimentary rock was originally like a layer cake, and the Haslam Formation is like a deep, dark c h o c o l a t e layer close to t h e b o t t o m of our cake. It is overlain by rocks very different in appearance. N e a r t h e top of t h e Haslam shale a curious t h i n g happens. T h e rocks begin to c h a n g e grain size. T h e fine m u d s t o n e and shale gradually change to sandstone w h i c h is t h e n abruptly overlain by an e n o r m o u s thickness of conglomerate t h a t looks s o m e w h a t like t h e c o n g l o m e r a t e on Sucia but is usually composed of larger cobbles. T h e transition is dramatic. For w h a t e v e t reason, t h e e n v i r o n m e n t where, for more t h a n 1 million years (and perhaps as long as 5 million years) only fine mud particles accumulated on t h e b o t t o m of the sea suddenly began to receive gravel, pebbles, and larger h u n k s of rock. This transition clearly records a dramatic c h a n g e in t h e e n v i r o n m e n t a l history of the region. It also marks a c h a n g e in formations. T h e top of t h e Haslam Form a t i o n is marked by t h e last m a r i n e shale. In many cliff faces and river cuts, we c a n observe t h e rocks t h a t succeed t h e shale; they are composed of very p r o m i n e n t conglomerates. T h i s lithological transition defines t h e boundary between t h e fotmations.

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In places, these conglomerates ( w h i c h are called t h e Extension Formation), are also as m u c h as a t h o u s a n d feet in aggregate thickness. W h e r e this formation is exposed, as on the south face of W a l d r o n Island, we see only a huge wall of rounded rocks all jumbled togethet, with only t h e faintest h i n t of sedimentary bedding. N e a r their top we see t h e m t h i n a n d c h a n g e to smallet clast sizes, eventually to be succeeded by siltstone with fossils. If we c o n t i n u e our t o u t t h r o u g h t h e N a n a i m o G r o u p , we find at least five such transitions from fossil-bearing shale to more coatsely grained deposits without fossils. T h i s a l t e r n a t i o n b e t w e e n m a r i n e deposits and marginal marine or terrestrial deposits t h a t makes up t h e N a n a i m o G r o u p continued until the end of t h e Age of Dinosaurs. T h e section on Sucia is roughly in the middle of this long history. W h y do such dramatic changes in lithology take place? Normally only two explanations are offered. Either t h e level of the land is rising or falling (which happens w h e n m o u n t a i n s form nearby), or the sea level itself is changing. It is the latter explanation that is now favored in most cases. If this explanation is correct, the level of the sea rose dramatically over a 20-million-year period and t h e n receded at least five times. Sucia Island was deposited during the third of these cycles. A r e these cycles the result of a c h a n g e in sea level? Every day the sea rises and falls, its tide a clock of n a t u r e . A l t h o u g h we think of tides as coming in and going out (we h a v e e v e n i n v e n t e d two words for the p h e n o m e n o n , flood and ebb), the c h a n g e is more a vertical t h a n a horizontal effect. T h e tides are familiar to all of us as a n o r m a l consequence of gravity, a large m o o n so near, and a sun tugging on everything. Tidal change is usually imperceptible—unless you live in t h e Bay of Fundy, where it takes a steady trot to o u t r u n the tide. T h e tides ate t h e most familiar change in what we may call sea level. Yet daily tidal change is n o t t h e only routine c h a n g e in sea level; it is only the fastest. T h e r e are longer-term changes t h a t are far less intuitive and familiar. Off the east coast of N o r t h America, for instance, fishing boats routinely trawl up cobbles and rocks indicative of the seashote from depths as deep as 150 metets. T h e teeth of mastodons and m a m m o t h s are found in this

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way as well, and unless these great Ice Age elephants of N o r t h America were swimmers far from shore (doubtful), or had their t e e t h somehow transported to locales many miles off the shoreline (equally doubtful), we can conclude that during t h e Ice Ages, t h e level of t h e sea was far lower from what it is now. T h e sea has indeed b e e n quite unstable in its position telative to the land's surface. Sea level routinely changes, although t h e rate of change is so slow t h a t no c h a n g e would be observable in a h u m a n lifetime, or e v e n many lifetimes. H o w does this h a p p e n ? H o w did science make this discovery? T h a t t h e sea does c h a n g e in level over time has been k n o w n for nearly two centuries. W h e n n i n e t e e n t h - c e n t u r y geologists discovered the reality of the Ice A g e s — w h e n it b e c a m e clear that the e n o r m o u s quantity of ice covering so m u c h of c o n t i n e n t a l land surfaces could h a v e come only from the sea—they realized t h a t t h e consequences of such an e v e n t would be a lowering of sea level. So large are t h e volumes of water required that fresh water on land could n o t h a v e produced t h e necessary volumes of ice. Large portions of water were extracted from t h e sea to be turned into ice. Normal runoff back into the sea did n o t take place. More and more water became contin e n t a l ice, and t h e level of t h e o c e a n began to fall. T h e most recent Ice A g e was n o t a single event, but the alternation of more t h a n 20 individual glacial advances and retreats covering t h e last 2 million years of e a r t h history. Each glacial a d v a n c e and retreat caused a corresponding retreat and a d v a n c e of sea level. W h a t is so extraordinary is the rapidity and magnitude of these changes: drops and rises of as m u c h as 150 meters. We h a v e arrived at two causes of c h a n g e in sea level—tides, which cause changes of up to 15 meters w i t h i n a single day, and c o n t i n e n t a l glaciation (and growth of icecaps), w h i c h causes changes over thousands of years. But t h e r e is a third type of sea level c h a n g e t h a t is far slower. It is currently the subject of intense research by a p h a l a n x of e a r t h scientists, and the impetus for this sustained research comes from t h e oil companies. According to many earth scientists, this third type of sea level c h a n g e is brought about by long-term changes in t h e volume of the ocean basins. T h e s e changes, called

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eustatic sea level changes, take place over t i m e scales measured in h u n d r e d s of thousands of years. Eustatic changes appear to he caused by the same processes t h a t bring about c o n t i n e n t a l drift. T h r o u g h plate t e c t o n i c processes (so goes t h e most popular theory), the volume of t h e ocean basins increases or decreases, a n d these volumetric changes are sufficient to cause t h e oceans to spill o n t o land surfaces and flood the lowland areas of all c o n t i n e n t s . T h e m e c h a n i s m t h a t causes this volumetric c h a n g e is t h e rise and fall of m i d - o c e a n "spreading centers," such as the mid-ocean ridge e x t e n d i n g t h e length of t h e A t l a n t i c . We k n o w t h a t sea floor spreading is caused by c o n v e c t i o n of t h e earth's m a n t l e region and t h a t the giant plates (which can include b o t h oceans and c o n t i n e n t s on t h e same plate) sit atop these gigantic c o n v e c t i o n cells. C r e a t i o n of n e w o c e a n i c crust occurs at the spreading centers, and if t h e rate at w h i c h h e a t rises in these regions increases, t h e spreading centers themselves increase in volume. W h e n heat flow diminishes, the spreading centers c o n t r a c t . T h e y act like gigantic m o u n t a i n ranges that inflate or deflate in response to t h e h e a t w i t h i n t h e m . T h e changing volume of rock w i t h i n t h e spreading centers causes t h e changes in sea level. W h e n spreading centers receive more h e a t and increase in volume, the net effect is to decrease t h e ocean basin volume and cause water to flow out of the oceans o n t o land surface, m u c h like a b a t h t u b overflowing. Sea level rises. T h e opposite occurs w h e n h e a t flow decreases, and the spreading c e n t e r subsides. Sea level drops. T h e magnitude of these changes can be e n o r m o u s . N e a r t h e e n d of t h e Age of Dinosaurs, t h e sea may h a v e been at its "highest" stand ever; half of N o r t h America, as well as huge regions of all o t h e r c o n t i n e n t s , were covered with shallow inland seas. N o r t h A m e r i c a was really two c o n t i n e n t s : o n e east, one west, with a seaway e x t e n d i n g from t h e Rocky M o u n t a i n s to near the Appalachians and from t h e A r c t i c Circle to t h e tropics. A n d because t h e "seven seas" are really a single global ocean of i n t e r c o n n e c t e d water, any change in sea level is global. T h e concept t h a t long-term global changes occur in sea level has launched a rising star a m o n g t h e geosciences; t h e field of sea level change. A

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n u m b e r of new terms h a v e b e e n coined to describe all the manifestations of sea level c h a n g e : high stands (times of sea water high levels), low stands (the opposite), o n l a p (a landward migration of underwater deposits as the sea slowly floods a c o n t i n e n t a l surface), offlap ( t h e opposite), transgression (a slow flood of c o n t i n e n t a l regions caused by rising sea level), and regression ( t h e opposite). T h e field of sea level c h a n g e remains o n e of the most intensively studied disciplines of geology, because it has b e e n so useful in finding oil. It is also useful in d e t e r m i n i n g b o t h time and t h e character of past environments. A q u a n t u m leap in our u n d e r s t a n d i n g of sea level c h a n g e came about in t h e 1960s and 1970s with t h e i n t t o d u c t i o n of "seismic stratigraphy." G e ologists discovered t h a t by tracing t h e p a t h of shock waves m o v i n g through rock, they could observe structures deeply buried u n d e r t h e earth's surface. W h e n charges of d y n a m i t e are e x p l o d e d a b o v e a buried pile of sedimentary rock a n d t h e reflections of these shock waves are followed t h r o u g h t h e rock w i t h recording i n s t r u m e n t s , very detailed t h r e e - d i m e n s i o n a l pictures of t h e stratigraphy emerge. U s i n g this methodology, t h e geologists recognize o n l a p and offlap deposits in s e d i m e n t n o w deeply buried. T h e oil companies h a v e found ( a n d still find) a great deal of oil in this way. O v e r many years, scientists also n o t i c e d t h a t in m a n y different parts of t h e world the sea level curves—diagrams illustrating sea levels t h r o u g h t i m e — s e e m e d to m a t c h up. But do t h e various sea level curves really m a t c h up, or are we seeing different curves in every individual ocean basin? To find out, you need excellent time control correlation m a t c h i n g t h e various sedimentary rocks that record t h e sea level c h a n g e s — i n t h e o t h e r words, you need to be able to recognize t h e age of sediments in widely disparate tegions. W i t h o u t great time control, t h e a c c e p t a n c e or rejection of global sea level curves could n o t be completed. By some strange c o i n c i d e n c e , t h e latter part of the Cretaceous seems to hold as m u c h oil as, or e v e n more oil t h a n , rocks of any o t h e r age. Yet for reasons outlined in t h e first several chaptets of this book, the sea level curves for t h e latter part of t h e Cretaceous Period h a v e been a m o n g t h e least

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well known, because it has been so difficult to find and decipher the C r e t a ceous time markers on a global scale. Five sea level oscillations are present in t h e sedimentary rocks of Late Cretaceous age in the Vancouver Island region. A r e these regional or global changes? O n l y by studying rocks of similar age in m a n y o t h e r regions could this be ascertained.

Sea level c h a n g e and life Sea level c h a n g e is certainly an i m p o r t a n t e n v i r o n m e n t a l factor t h a t affected a n c i e n t e n v i r o n m e n t s , but it may play an e v e n more important role in governing t h e nature of life on earth. For more t h a n a century, sea level change has been considered o n e of t h e leading causes of mass extinctions, which turn out to be t h e largest-scale evolutionary p h e n o m e n a t h a t affect our planet's biota. Mass extinctions are global catastrophes t h a t h a v e caused large n u m bers of species to become e x t i n c t in t h e geological past. A mass e x t i n c t i o n event can last between a t h o u s a n d a n d several million years. T h e r e h a v e been about 15 such events during t h e last 500 million years of e a r t h history (the time of skeletonized life on this p l a n e t ) . Five of these are classified as "major" in that they caused more t h a n half of all species t h e n living to go extinct. T h e most d e s t m c t i v e mass e x t i n c t i o n e n d e d t h e Paleozoic Era. T h e second most destructive ended t h e Mesozoic Era, of w h i c h t h e Cretaceous is the last unit. T h i s " K / T " mass e x t i n c t i o n e n d e d t h e A g e of Dinosaurs and brought the Cretaceous Period to an end as well. T h e possible association between sea level c h a n g e and mass e x t i n c t i o n was recognized early by geologists. More t h a n a century ago, it was noted that each of t h e major mass e x t i n c t i o n s seemed to h a v e occurred soon after a sudden and precipitous drop in global sea level. Yet by what m e c h a n i s m might a simple drop in sea level h a v e caused planetary d e a t h on a global scale? T h e r e is no doubt t h a t several of the major mass e x t i n c t i o n s occurred

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either during or immediately after a great sea level change. Might this have b e e n only simple coincidence? T h e rising or falling of t h e sea's surface would probably n o t itself kill a n y t h i n g (unless, of course, it caused shallow seas to disappear, thus killing all of the trapped i n h a b i t a n t s ) . However, t h e c h a n g e in sea level could trigger a m u c h more deadly killer: catastrophic global climate change. As sea level drops, land area increases relative to t h e area of t h e sea; this, in turn, stimulates climate c h a n g e , because temperature fluctuations on the earth's surface are significantly influenced by t h e relative a m o u n t s of ocean and land area. Sea level c h a n g e can also reconfigure the geography of the earth, and this too plays a part in t h e n a t u r e of oceanic current systems. Because organisms are usually quite narrowly adapted to specific climates, sudden climate c h a n g e is a plausible "kill m e c h a n i s m " associated with sea level change. Geologists of my g e n e r a t i o n were thus faced with several very interesting questions about sea level c h a n g e . Was it global? A n d did a major sea level c h a n g e occur at t h e very e n d of the Cretaceous Period and thus create a climate c h a n g e t h a t e x t e r m i n a t e d t h e dinosaurs and m u c h else? T h e s e are two different questions, and n e i t h e r could be tested by using observations of rocks only in o n e area. Furthermore, t h e fact t h a t the Cretaceous rocks in the Vancouver Island region occurred on either isolated islands or isolated riverbeds left m u c h of t h e c o m p l e t e record of time in this region covered by t h e sea or by a sea of vegetation. A different succession of sedimentary rocks of this age needed to be studied, rocks with better c o m p l e t e exposure, a place where n e i t h e r t h e sea n o r vegetative cover was present. A desert region was needed, but a desert region near t h e European type regions so as to ensure good time correlation. After some deliberation, an international group of geologists chose a thick exposure of sedimentary rocks found in central Tunisia. It was decided t h a t an expedition would be m o u n t e d to look at these rocks in order to determine w h e t h e r the mass e x t i n c t i o n e v e n t at the end of the Cretaceous was c o i n c i d e n t w i t h a major drop in sea level. I was invited, and I was eager to go for many reasons, n o t t h e least being to see w h e t h e r t h e sea level changes I

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had long observed in the Vancouver Island area could be recognized in Tunisia as well.

The verdict All the others had gone, leaving me alone in t h e empty hotel in El Kef. It was very cold. I had come to El Kef, Tunisia, in April of 1992 to help conduct the crucial observations concerning sea level change and the " K / T " mass extinction represented by the region's strata and fossils. T h e rocky country did not disappoint. Tunisia has some of the best exposures of t h e Cretaceous/Tertiary boundary known in the world, so it had been chosen as t h e site of a test to determine whether the great mass extinction that ended the Age of Dinosaurs— thought to h a v e been caused by climate c h a n g e , or sea level c h a n g e , or e v e n by the collision of a great c o m e t with t h e e a r t h — w a s a sudden, short-term or a slow, more gradual e v e n t . Two dozen scientists had c o m e here to collect sedimentary rock from either side of t h e Cretaceous/Tertiary boundary in order to see w h e t h e r t h e enclosed fossils disappeared right at t h e " K / T " boundary or did so gradually well below t h e boundary and to see w h e t h e r t h e geological evidence suggested t h a t t h e e x t i n c t i o n coincided with a drop in sea level, as so many had postulated. If t h e latter were true, t h e n a sudden dtop in sea level just might be o n e of t h e most extraordinary killers on the planet. We were especially interested in t h e n a t u r e of strata found in the last meters of the Cretaceous. If sea level were dropping here, we would expect to find evidence of shallowing water, and thus coarser-grained strata, as we approached t h e " K / T " boundary

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methodology, our "time m a c h i n e , " was t h e same as t h a t used on Sucia Island in the account earlier in this chapter. We "walked" t h e section, making detailed measurements of the stratal thickness and m i n u t e observations about every aspect of the rocks: their grain size, their color, t h e types of fossils present (or absent), the nature of sedimentary structures such as ripple marks or

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cross beds, t h e presence or absence of conglomerates, and any trends discernible in these features. No high technology was needed—just detailed observation carefully recorded in field notebooks. After several days of this our results were clear. T h e r e was no evidence of a sudden drop in sea level c o i n c i d e n t with the great mass extinction. In fact, we found just t h e opposite. T h e water in this region (and in many others, it t u r n e d out) was deepening w h e n the e x t i n c t i o n occurred, n o t shallowing. Sea level was n o t t h e culprit. A b u n d a n t evidence eventually showed t h a t eatth's collision with a gteat c o m e t in t h e Yucatan region of Mexico was t h e real killer. At t h e end of a week t h e various geologists left for their h o m e countries. I stayed on to spend more time in the field, for my work here was still unfinished. T h e hills in this part of Tunisia c o n t a i n thick successions of sedimentary tock exactly t h e same age as t h e sedimentary rocks in the Vancouver Island region. H e r e was an ideal test of t h e hypothesis that sea level c h a n g e is nearly always caused by global events rather t h a n due solely to local events such as regional uplift, w h i c h might be caused by m o u n t a i n building. H e r e I could see w h e t h e r t h e p a t t e r n of sea level change so wonderfully exposed on t h e various islands of t h e Vancouver Island region was caused by global rather t h a n regional processes. El Kef is located in t h e central part of Tunisia and is at sufficient altitude t h a t spring comes late. It seemed ironic to be so cold here, for to the south of us lay broad desert regions, giving way to t h e patched and hot Sahara. It was a small town, with few of t h e W e s t e r n trappings that characterize t h e larger cities fatthet n o r t h in Tunisia. A truck with a loudspeaket drove t h r o u g h t h e t o w n each m o r n i n g and evening, calling the faithful to the mosque. A r a b m e n t h r o n g e d t h e bars and cafes, but few w o m e n were to be seen. I could feel t h e discipline of t h e place, and its strangeness to me was palpable. T h e days in t h e field were long and exhilarating. T h e rocks were laid out as if by giant brushstrokes across t h e face of t h e low m o u n t a i n s , alternations of thick limestone and dark shale stteaked across t h e rugged countryside. A m m o n i t e s had been reported from here but had barely been studied. I 122

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had assumed they would he rare and so was delighted to find t h e m in abundance. In places they were almost stacked together and elsewhere they were rare, with no apparent reason for their curious distributions. T h e limestone contained the most a m m o n i t e s , and it was t h e r e t h a t I spent most of my time, scanning rock surfaces for t h e telltale sign of ribs or a spiraled shape. T h e most c o m m o n forms had shells t h a t looked like giant snails, rather t h a n the usual coiling in o n e pale t h a t typified t h e vast majority of a m m o n i t e s . O n e particular species was especially c o m m o n , a form called Bostrychoceras polyplocum well k n o w n from Europe. Rocks c o n t a i n i n g this particular ammonite may be exactly time-correlated with t h e rocks of Sucia Island, and like the rocks on Sucia, t h e sediments encasing this particular a m m o n i t e showed evidence of increasing water d e p t h . Limestone and shale: a d a n c e of ancient rock, o n e telling of a d e e p e n i n g sea, the o t h e r of dropping sea level. T h e Tunisian rocks were beautifully exposed; there were no missing intervals due to faulting, no covered intervals due to vegetation. In this regard they were completely unlike the rocks I had long studied in t h e Vancouver Island region, where t h e strata are found only on seacoasts or in river gorges. Here, in this Tunisian semi-desert, they are inescapable. T h e y are t h e land itself, the skeleton of this country with t h e bones exposed. T h e very a b u n d a n c e and completeness of t h e rock record here enabled me actually to see how important sea level c h a n g e is in d e t e r m i n i n g t h e nature of sedimentary rocks. T h e r e appeared to be many different cycles of change superimposed on one another. Long-term changes visible in thousandfoot increments of sediment (and thus talking place over millions of years) were made up of shorter-term fluctuations visible in hundred-foot increments. T h e s e changes could be read in t h e way t h e rocks looked, in t h e way they were bedded, and in t h e way their enclosed fossils changed. I could see shallow-water organisms being replaced by deeper-water assemblages as I moved up through thousands of feet of strata in this region, and t h e n I could watch the opposite occur. T h e level of t h e sea h a d b e e n t h e mastet here, dictating so many aspects of the formation of sedimentary rocks long ago. In turn, the ancient rocks themselves dictate h o w t h e land looks today, n o t just in the colors of the dark shale and white limestone, but t h e very n a t u r e of 123

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the landscape itself. T h e limestone is far harder t h a n t h e shale and less easily eroded; because of this, t h e limestone makes up the ridges and high places, and t h e softer shale is usually found at lower elevations. You can literally m a p t h e topography by mapping t h e limestone and shale, its locations brought about by a n c i e n t changes in a n c i e n t sea level. Worldwide units. It seemed t h e very essence of circularity. It took highprecision, worldwide correlation t h r o u g h fossils and radiometric dating to c o n v i n c e scientists t h a t t h e fluctuations in sea level, as deduced from the rocks left behind, were worldwide in scope. Yet o n c e t h a t had b e e n proved, the very changes in sea l e v e l — t h e worldwide sea level c u r v e — b e c a m e a new sort of clock, a n e w way of telling time. O n c e you find your place in the sea level curve, you c a n m a k e powerful predictions about time. It would seem t h a t t h e r e could be no two places more dissimilar t h a n the green islands of t h e Vancouver Island region of N o r t h A m e r i c a and the deserts of n o r t h e r n Africa. T h e rocks are equally dissimilar: the dark olive sandstone and shale of t h e N a n a i m o G r o u p and the white limestone of Tunisia. Even t h e fossils in b o t h regions are different, and no species comm o n to b o t h exists. But they are united by their age: Both sets of rocks were deposited between 80 and 65 million years ago, and being of the same age, they experienced the same fluctuations in sea level. T h e simplest of all time m a c h i n e s , detailed observation, has shown us t h a t this is so and has elucidated two a n c i e n t places and their e n v i r o n m e n t s .

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F a r up t h e Inside Passage, Vancouver Island begins to nestle inward toward mainland British C o l u m b i a , and t h e frigid water begins to warm a bit as t h e Georgia Strait narrows. T h e salmon fishing improves, and t h e feel of wildness increases. Many small towns dot t h e countryside, most surviving on logging, tourism, and t h e groceries sold to folks in retirement double-wides. It is certainly n o t t h e U . S . A . , for t h e subtle but distinct feel of C a n a d a is perceptible everywhere. T h e nature of t h e rocks begins to c h a n g e as well. Fossils in this part of Vancouver Island are no longer found on t h e seacoast. To find fossils this far north, you h a v e to trek inland on t h e logging roads winding t h r o u g h t h e second- or third-growth forest, where isolated canyons of shale h a v e been 127

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cut deep into t h e countryside by t h e region's many rivers and creeks. T h e n a m e s of these watercourses reflect a heritage of native C a n a d i a n s and logging moguls: Tsable, Bloedel, Trent, Puntledge, Btowns, N a n a i m o , Qualicum, Little Q u a l i c u m , Haslam, C o w i c h a n , C h e m a i n u s ; each is a river where the dark shale and their enclosed a m m o n i t e s lie exposed. All have rocks older t h a n either Sucia or Hornby, a n d t h e a m m o n i t e s are different, too. T h e two most c o m m o n are uncoiled species—one a giant snail shape, the other an o p e n spiral; b o t h are exquisite to find and behold, real heart thumpers. Elsew h e r e in t h e dark strata are m a n y types of clams a n d snails, but in forms associated with deep-water e n v i r o n m e n t s . I c a m e w i t h a crowd in 1994 to see these creeks and t h e i t fossil fauna: friends from t h e local S e a t t l e m u s e u m , my son, and a Seattle reporter n a m e d Roger Downey. All h a d c o m e for a week of fossil collecting. We c a m p e d along t h e rivers a n d e x c a v a t e d in t h e dark shale, m o v i n g n o r t h ward up t h e east coast of V a n c o u v e r Island and its N a n a i m o G r o u p deposits. It was a perfect lazy s u m m e r trip; no pressing agenda, beautiful fossils, a good group. O n e of our last stops was t h e t o w n of C o u r t n e y , sprawled along t h e b a n k s of t h e P u n t l e d g e River. C o u r t n e y sported s o m e t h i n g n o n e of t h e o t h e r small logging t o w n s h a d : a museum. A n d in this museum reposed t h e most extraordinary fossil ever collected in British C o l u m b i a : a 50-foot-long elasmosaur. A l t h o u g h t h e A g e of Dinosaurs is r e n o w n e d for its sautian b e h e m o t h s on land, t h e seas supported large and exotic reptilian wildlife as well. G r e a t sea lizards and long-necked reptiles occupied roughly t h e niche of today's t o o t h e d whales. Yet prior to t h e late 1980s, n o t a single b o n e of any of these creatures had ever b e e n found in t h e Vancouver Island region, and it was t h o u g h t t h a t perhaps these great sea serpents had n o t lived in this region of the world, 80 to 70 million years ago. T h a t perception was radically changed by an a m a t e u r fossil h u n t e r prowling t h e banks of the Puntledge River. T h e skeleton was extraordinary, as was t h e story of its recovery. A local resident, Mike Trask, was wandering t h e edge of the Puntledge, looking for a m m o n i t e s , w h e n he spotted a most unusual fossil just sticking out of the

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riverbank. It turned out to be t h e vertebra of a large marine reptile. Trask soon spotted o t h e r vertebras, and various o t h e r bones as well. Large excavating e q u i p m e n t was brought in, and over several m o n t h s t h e remains of this creature—intact and c o m p l e t e — w e r e removed from its lithic t o m b . Specialists from the Royal Tyrell M u s e u m in A l b e r t a were brought in to h e l p with skull preparation, but it was largely a local p r o d u c t i o n . T h e best part of this story is t h a t t h e skeleton stayed h o m e . It was n o t sold for big bucks; it was n o t exiled to some far off museum. It stayed in Courtney, and a museum grew up around it. T h i s particular find galvanized t h e paleontological c o m m u n i t y in British Columbia and elsewhere. Simply knowing t h a t such fossils were pres* ent in the Vancouver Island region sharpened eyes grown c o m p l a c e n t and brought new collectors to t h e region to search for this type of fossil treasure. Before long several more finds were made. Perhaps t h e most exciting came from Hornby Island, at the same site where we had drilled for paleomagnetics. On Fossil Beach, o n e of t h e best of northwest collectors, a m a n n a m e d G r a h a m Beard, found the region's first mosasaur fossil. T h e presence of a mosasaur, a large m a r i n e lizard, sent a n y o n e w h o had discovered a m m o n i t e s in this region scurrying back to look at their fossils, for mosasaurs are t h o u g h t to h a v e b e e n t h e most i m p o r t a n t of all a m m o n i t e predators. T h i s conclusion had c o m e from supposedly telltale bite marks found on many a m m o n i t e shells. T h e past is time and place. But it is life, t h e i n h a b i t a n t s , as well. T h e fossil themselves t h a t we find are time m a c h i n e s , for they as m u c h as any other information can transport us back into deep time. But as we shall see in this chapter, the study of fossils is fraught with uncertainty and with multiple paths of interpretation. T h e fossils are t h e data: T h e y are t h e real o b jects coming to us from deep time, and as is written on many a laboratory door, "Good data are immortal." But data are as naked as t h e skeletons we find; they need to be prepared and interpreted. T h o u g h t h e data are immortal, the interpretations are n o t . To put interpretations to t h e test, scientists all over the world invoke a n o t h e r time m a c h i n e .

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Evidence of ancient predation A seashell pressed to t h e ear will evoke t h e sound of surf, aural waves on some far tropical beach, t h e t o n e of t h e sea. But any seashell records far more t h a n an imaginary surf. Shells bear t h e equivalent of a tree's rings, giving us age and clues to e n v i r o n m e n t ; all shells m a i n t a i n a record of their life and times, and sometimes t h e t i m e and m a n n e r of their d e a t h . O n e of the properties of sea shells—including ancient sea shells—is t h a t they are faithful recorders of age-old predation. M u c h information about the past comes from reading the record of shell breaks t h a t offer an account of some a n c i e n t predatory attack. Interpreting breaks in fossil shells is an important and widely used means of bringing the past back to life. T h e shells and their breakage patterns, t h e n , are the data. But our interpretation of what caused those breaks can be far more ambiguous. M a n y fossil shells show breaks. Sometimes t h e attacks t h a t caused these breaks killed the animal w i t h i n . Often, however, t h e predator did n o t succeed in killing its shelled quarry, leaving t h e organism to repair the breaks and, in t h e process, leaving a scar behind, yielding fascinating infotmation about w h o ate w h o m in a n c i e n t time. Sometimes, however, the investigators zeal for such investigations outstrips t h e evidence. A n d w h e n such excitement is coupled with an incomplete or faulty understanding of h o w shell material fails under pressure or point load, misinterpretations can ensue. T h e following is just such a cautionary tale. It n o t only pitted those w h o understand the m e c h a n i c a l and material properties of molluscan shell against those who don't but also cast into sharp relief a clearly sensational explanation for fossil evidence against a far more prosaic—yet in this case accurate—portrayal. A m m o n i t e shells often h a v e round marks in t h e m . Were these holes left by the dramatic attack of a marine lizard of great size and strength or by the slow rasping of a tiny snail shell over many years? A r e these holes t h e bite marks of a creature whose closest living relative is t h e K o m o d o dragon? T h e K o m o d o dragon is a large lizard (up to 10 feet long) t h a t now lives only on several small Indonesian islands, where it preys mainly on small deer and pigs, killing t h e m w i t h a saliva rendered poisonous by highly toxic bac130

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teria. T h e K o m o d o d r a g o n is t h u s a most impressive c r e a t u r e . However, the m o d e r n lizards are dwarfed by t h e i r ancestors from t h e A g e of Dinosaurs, w h i c h were 30 to 40 feet in l e n g t h a n d were, during t h e heyday of the dinosaurs, t h e most successful a n d largest of all seagoing vertebrates. A l t h o u g h relatively few people h a v e seen a K o m o d o dragon (and no one has ever seen a living mosasaur, because t h e last of t h e m died out at t h e end of t h e Cretaceous Period, killed off no doubt by the lingering effects of the comet t h a t ended t h e Mesozoic Era), their family is fairly well k n o w n to us. All, t h e living a n d t h e dead alike, are m o n i t o r lizards, a group still highly successful in many parts of t h e world. Long ago, during t h e Cretaceous Period, giant m o n i t o r lizards—the mosasaurs—were t h e largest and most ferocious carnivores in t h e sea. Mosasaurs were n o t t h e only large reptiles in t h e sea, of course. Two other oceangoing reptiles also vie for our a t t e n t i o n in t h e Mesozoic rock record: the long-necked (and sometimes short-necked as well) creatures k n o w n as plesiosaurs ( t h e archetype for t h e Loch Ness monster) and t h e more fish-like (or dolphin-like) forms called ichthyosaurs. T h e latter were extremely a b u n d a n t in t h e Jurassic, but by t h e Cretaceous Period they were eclipsed in n u m b e r (and certainly in size) by t h e mosasaurs and plesiosaurs (elasmosaurs, such as the type found on t h e Puntledge River, are a type of plesiosaur). Ichthyosaurs and plesiosaurs were n o t dinosaurs e i t h e r — i t appears t h a t no true dinosaurs m a d e t h e evolutionary leap back i n t o t h e sea. Mosasaurs were very late arrivals to t h e Mesozoic world. U n l i k e plesiosaurs and ichthyosaurs, w h i c h c a n be traced well back into t h e earliest epochs of t h e Mesozoic Era, mosasaurs first appeared in t h e Late Cretaceous. Until the discoveries on Vancouver and H o r n b y Islands, they were largely absent from the west coast of N o r t h A m e r i c a , h a v i n g b e e n found only at a few localities in California. All mosasaurs had four flippers, with t h e toes e x p a n d e d into web-feet. T h e bodies were long, t h e tail e v e n longer. S o m e h a d tails with a large caudal fin as well, a structure u n k n o w n in our world's lizards. As in modern-day whales, the bones of t h e pelvic region were reduced, making l o c o m o t i o n on land almost impossible. Yet unlike whales, w h i c h h a v e lost any semblance of I SI

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a neck, t h e mosasaurs retained distinct head tegions set apart ftom the body by a strong, if short, neck. T h e head itself was out of some n i g h t m a t e . Flat and narrow with a long, tapering snout, its most distinguishing characteristic was t h e n u m e r o u s t e e t h . T h e jaws, like those of most vertebrate animals, were lined above and below with n u m e r o u s dagger-like teeth. But the palate bones had t e e t h as well, a second set also conical and tapering well back in the roof of t h e m o u t h . Clearly, these were creatures evolved to bite. Finally, t h e r e is t h e m a t t e r of t h e t o n g u e . All ptesent-day m o n i t o r lizards have a forked tongue, like a snake's. In all probability t h e mosasaurs of the ancient world were similarly e n d o w e d . No w o n d e r t h e s e cteatures are favorites of illustrations depicting the Mesozoic seaways, for here is a monster every bit as frightful as any T. rex or any of t h e v e r m i n emerging from the imagination of H. P. Lovecraft. Imagine some sort of odious (but spectacular) gladiatorial c o m b a t b e t w e e n mosasaurs and killer whales of our world or between a mosasaur and a great white shark. I would bet on t h e mosasaurs. W h y did t h e lizard-ancestors of t h e mosasaurs go back into t h e sea? W h y a b a n d o n t h e rich, tropical rainforests of t h e Mesozoic Era, a time w h e n

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jungle largely covered the land, for life in t h e sea? We might also ask the marine iguanas of our day, w h o h a v e t a k e n t h e same step. ( T h o u g h n o t so giant a step: M a r i n e iguanas are fully amphibious, being as adept on land as in the sea, whereas the mosasaurs may h a v e left t h e sea only to lay eggs—or n o t at all, giving live birth in t h e sea just like ichthyosaurs and whales.) T h e answer to all these questions may be t h e same: food. T h e sea is rich in resources, and the lure of t h a t food has caused many lineages of animals to return to t h e place of their ultimate ancestry. A n d if it was food t h a t induced a previously obscure lineage of small m o n i t o r lizards to a b a n d o n t h e land in t h e Late C r e taceous, what was t h e n a t u r e of t h a t food? T h a t particular answer is on display in virtually every natural history m u s e u m on earth. T h e seas of t h e Mesozoic were filled with those a n c i e n t shelled cephalopods called ammonites. U n c o u n t e d n u m b e r s of a m m o n i t e shells h a v e b e e n recovered from Cretaceous-aged deposits bearing n u m e r o u s circular holes t h a t closely m a t c h the size and shape of mosasaur teeth. Case closed: Mosasaurs ate a m m o n i t e s and left a record of their feasts b e h i n d , dramatic s t a t e m e n t s of a n c i e n t predation. A n d so it is t h a t countless natural history museums, if n o t lucky e n o u g h to h a v e a mosasaur skeleton to display, at least can show an a m m o n i t e shell bitten, supposedly, by a mosasaur. T h e only problem is t h a t in every case examined to date by a t e a m of Japanese and C a n a d i a n scientists t h a t has scrutinized this famous paleontological lore, t h e so-called mosasaur bite marks are anything but the work of gnashing mosasaur t e e t h . In fact, they h a v e a

Fossil Mosasaur of Cretaceous Age. 133

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far more prosaic cause: T h e y appear to be n o t h i n g more exotic t h a n the resting holes of circular m a r i n e snails called limpets; resting holes are small depressions t h a t limpets drill into t h e shell or rock t h a t serves as a h o m e territory. S u c h a radical reinterpretation has predictably caused howls of protest. W h a t is t h e origin of this interpretation, first m a d e in 1960, that t h e circular

Diagram showing ammonite shell and position of so-called mosasaur bite marks. (From Kauffman and Kesling, 1960.) 134

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holes found on so many U p p e r C r e t a c e o u s a m m o n i t e s are mosasaur bite marks, and why (ot h o w ) was it s h o w n to be wrong?

A tempting interpretation T h e story began in t h e early 1960s and was originated by o n e of the most flamboyant and colorful characters ever to h a v e studied t h e deep past, Erie Kauffman. Erie, as he is k n o w n to all, remains o n e of t h e most revered of living paleontologists. He grew up in t h e west, and during his long career he became perhaps the finest field paleontologist of t h e t w e n t i e t h century, specializing in the paleontology and stratigraphy of Cretaceous rocks. His major study area has been t h e great W e s t e r n Interior Seaway of t h e U n i t e d States, the large sea that split t h e land area of N o r t h A m e r i c a in half, r u n n i n g from n o r t h to south. T h i s seaway was t h e h o m e to u n c o u n t e d a m m o n i t e s , and not a few mosasaurs as well, judging from t h e large numbers of skeletons t h a t have been collected over t h e years from formations such as t h e Pierre Shale and the Niobrara chalk. S o m e w h e r e , early in his career, Erie came to t h e conclusion t h a t mosasaurs must h a v e e a t e n a m m o n i t e s . T h e logic is impeccable. T h e very a b u n d a n c e of a m m o n i t e s in C r e t a ceous oceans must h a v e made t h e m a t e m p t i n g a n d attractive food source for many types of marine carnivores. Because many a m m o n i t e s were large (many species had shells over 3 feet in d i a m e t e r ) , they would h a v e b e e n a very appropriate prey for t h e mosasaurs—providing, of course, t h a t t h e hard outer shell of t h e a m m o n i t e could be breached. Erie and his academic advisor A. Kesling at t h e University of M i c h i g a n fitst published this interpretation in 1960. T h e paper remains sprightly and readable. It starts as follows: An Upper Cretaceous a m m o n i t e of t h e genus Placenticeras has been found bearing numerous perforations and impressions made by the teeth of a mosasaur. . . . T h e shell was bitten tepeatedly, and bears dramatic evidence of t h e fatal encounter. From a composite

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of the patterns of t o o t h marks we h a v e reconstructed the dentition, and from the relationships of t h e upper and lower jaw we offer certain inferences on the shape of the head, the structure and action of t h e jaws, and the diet of the mosasaur. (Kauffman and Kesling, 1960, p. 193) T h i s scientific paper about the proposed mosasaur bite marks found in a m m o n i t e shells was so different in its style and tenor from t h e paleontologic papers of its time t h a t it stands out like a beacon. Paleontology in the 1950s had b e e n d o m i n a t e d by descriptions of a n c i e n t species, n o t descriptions of h o w those species lived, but here was a true interdisciplinary paper. N o t only did Kauffman and Kesling dare to describe mosasaurs ( t h e province and territory of "vertebrate" paleontologists), but in t h e same paper they described a m m o n i t e s , an "invertebrate" fossil. Specialists in t h e two fields at that time (and to some e x t e n t e v e n n o w ) rarely read e a c h other's papers and don't e v e n a t t e n d t h e same scientific meetings. W a s this a paper about mosasaurs, or a m m o n i t e s , or what? T h e paper was also fun to read. S o m e of the desctiptions sound far more like a novel t h a n like a learned scientific paper. Mosasaurs are characterized as h a v i n g a "pugnacious n a t u r e " and are described as "the most vicious, rapacious creatures of t h e w a t m e p i c o n t i n e n t a l seas during the epoch of theit existence." T h e Kauffman and Kesling papet dealt with one single fossil—and still managed to c o m e in at a length of 58 pages and to offer 7 figures and 9 fullpage plates of p h o t o s . Perhaps n e v e r in the history of paleontology has so m u c h b e e n written about a single fossil shell. T h e attack itself is described in blow-by-blow fashion, for Kauffman and Kesling believed t h a t their shell (which is indeed riddled with holes) was b i t t e n sixteen times. Each bite is described in detail. For instance, T h e initial bite resulted in eight imptessions on t h e shell. Teeth of t h e upper jaw struck the right side of the c o n c h , leaving marks of maxillary teeth. . . . A c c o r d i n g to our reconstruction of t h e

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mosasaurs d e n t i t i o n , based on a composite of all bites, all t e e t h represented in bite 1 are strongly developed. Since only t h r e e perforated the shell, the mosasaur did n o t exert m u c h pressure in this bite. . . . Since t h e bite was directed for the anterodorsal side of t h e a m m o n i t e shell, above its aperture, t h e animal may h a v e b e e n picked up from t h e b o t t o m or attacked while swimming at some distance below the surface. A n d so on, for fifteen more bites. T h e authors concluded t h a t t h e attack was directed at t h e upper side of the a m m o n i t e . T h e y t h o u g h t t h a t t h e mosasaur tried to swallow t h e entire a m m o n i t e , pulling it as far back into t h e t h r o a t as possible, and t h a t t h e mosasaur was in t h e habit of eating a m m o n i t e s . T h e plan of assault—seizure from above, a t t e m p t to swallow whole, and failing this, crushing t h e living c h a m b e r to squeeze out the soft parts—seems to indicate familiarity with t h e prey. T h e large, conical biting t e e t h and t h e wide intermaxillary angle appear to be adaptations for c a t c h i n g , killing, and swallowing or crushing big shelled animals, such as a m m o n i t e s . (Kauffman and Kesling, 1960, pp. 2 3 4 - 2 3 5 ) All in all, t h e paper was a sensation, and it l a u n c h e d Erie's career. T h e r e was only o n e huge, glaring problem: Was this t h e only mosasaur in the history of t h e world t h a t ate ammonites? Kauffman and Kesling conceded that this was t h e only specimen k n o w n with bite marks. Surely, if o n e mosasaur was such an avid (if i n c o m p e t e n t ) a m m o n i t e eater, t h e n o t h e r shells bearing other telltale bite marks should be k n o w n . Thirty years after his initial publication on this subject, Erie Kauffman was still c h a m p i o n i n g t h e idea t h a t mosasaurs bit a m m o n i t e s . By this time he had identified a n o t h e r 30 specimens w i t h "definite p r e d a t i o n marks" and at least this m a n y with "suspect" marks. F u r t h e r m o r e , Kauffman asserted that most of the confirmed predated a m m o n i t e s were attacked in a m a n n e r

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similar to t h a t described by Kauffman and Kesling, but "with greater efficiency," and he also n o t e d t h a t In most cases t h e initial crippling bite is directly followed hy a major bite or bites across t h e back of the ammonite's living c h a m ber, and rapid extraction of t h e soft parts from t h e shell. . . . T h i s seems to show a familiarity with t h e prey and a learned predation pattern; this and t h e increasing n u m b e r of k n o w n predated amm o n i t e s in t h e Late Cretaceous, suggest t h a t mosasaur predation on a m m o n i t e s was a normal but n o t d o m i n a n t food c h a i n relationship. (Kauffman, 1990, p. 185.)

M o s a s a u r s and me Two events in my life had sensitized me to the issue of mosasaurs and ammonites. T h e earlier had occurred more t h a n two decades before, during my first research trip to N e w C a l e d o n i a . My c o m p a n i o n on this trip, a zoologist n a m e d A r t h u r M a r t i n , placed a living nautilus in a tank full of large marine turtles. Nautiluses are n o t a m m o n i t e s ; t h e nautilus shell is thicker, and the septa within t h e shell are far less complex and convoluted. A n d sea turtles, of course, are unlike mosasaurs in many ways, n o t the least of which is their lack of a large m o u t h filled with teeth. Nevertheless, t h e result of this attack was quite impressive and was fatal to t h e nautilus, whose shell was fragm e n t e d into pieces large and small by the turtle's hard beak. T h e key observation was t h a t t h e turtle's attack on t h e nautilus resulted in a fragmentation of t h e s h e l l — n o t a h o l e or gouge left into t h e shell by the turtle's beak. Hit a potcelain plate w i t h a h a m m e r and you get a similar result, and for the same reasons. Mollusk shell (like porcelain) is composed of limy material t h a t is p r o n e to shattering u p o n impact. T h e second c h a n c e e v e n t t h a t piqued my interest in t h e "mosasaur bites a m m o n i t e " story occurred near Calgary, C a n a d a , in early M a r c h of 1996, w h e n I h a d a c h a n c e to visit t h e Royal Tyrell Museum. Sitting on the edge of the great A l b e r t a prairie, this m o d e r n museum houses the finest col138

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lection of dinosaur specimens in t h e world. But it holds o t h e r fossils as well, including a huge collection of a m m o n i t e s . By far t h e most a b u n d a n t of these belong to t h e genus Placenticeras, a large, discoid a m m o n i t e from the U p p e r Cretaceous and, coincidentally, t h e same genus first e x a m i n e d by Erie Kauffman in his pioneering mosasaur bite study. Placenticeras is an extraordinary fossil from an extraordinary creature. T h e fossil shells of this species are large for an a m m o n i t e ; specimens a meter in diameter are quite c o m m o n . ( T h e largest a m m o n i t e ever collected is about 3 meters in d i a m e t e r ) . In certain C a n a d i a n deposits they are very c o m m o n , surely mirroring their a b u n d a n c e in t h e shallow U p p e r Cretaceous oceans that covered this part of C a n a d a from 80 to 70 million years ago. T h e shells are compressed, like giant discs, and often are found with t h e motherof-pearl shell material still beautifully iridescent. It is w i t h i n t h e shells of this taxon t h a t the great p r e p o n d e r a n c e of circular holes h a v e b e e n f o u n d — t h e same holes originally described by Kauffman and Kesling as mosasaur bite marks. But in the Tyrell there are so many of these shells, collected over t h e years, that an efficient numbers game can be played: H o w many of t h e shells have holes, and do all or any of t h e h o l e marks suggest t h e spacing t h a t a mosasaur jaw would produce? My guide to t h e "mosasaur bites a m m o n i t e " story, as least as it was being played out in 1996, was Dr. Paul J o h n s o n of t h e Tyrell Museum, a specialist in U p p e r Cretaceous bivalves. S o m e m o n t h s earlier, J o h n s o n h a d been c o n t a c t e d by Dr. Tatsuro Kase, a researcher in Japan, asking w h e t h e r the Tyrell had a m m o n i t e s with circular holes in t h e m . Kase h a d b e e n studying U p p e r Cretaceous a m m o n i t e s from Japan and had begun to suspect t h a t many of the circular holes found in these a m m o n i t e s were t h e innocuous product of boring (literally and figuratively) limpets of t h e time, rather t h a n the exciting evidence of a n c i e n t predatory behavior. Kase visited the Tyrell's collections, a n d in every case t h e circular holes seemed to conform to t h e sizes and shapes produced by limpets. W h e n I heard this story, I had to laugh—I certainly preferred t h a t t h e many holes give us a glimpse into predatory sea monsters instead of snails. T h e clincher, at least to me, was t h a t t h e patterns of these holes seemed r a n d o m ; only o n c e 139

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in a while in this large collection would a shell show holes arranged in a row, looking for all t h e world like it h a d been produced by a row of biting teeth arranged along a linear jaw. A m o n t h after my visit to t h e Tytell Museum, t h e issue of mosasaur bite marks in a m m o n i t e shells was c e n t e r stage at a large m e e t i n g celebrating the A g e of Dinosaurs. T h e meeting, n a m e d Dinofest 2, was held in Tempe, Arizona. It was t h e second in a n o w - b i a n n u a l e v e n t exhibiting and discussing dinosaurs. T h e dinofests last a m o n t h and include a gymnasium-sized public display of many fine dinosaur skeletons and o t h e r fossils. A thtee-day scientific symposium held at t h e e n d of t h e T e m p e dinofest was attended by the brightest lights in t h e dinosaur h u n t e r s ' firmament: t h e A list, headed by Jack H o r n e r and Bob Bakker, and t h e B list, which was virtually everybody else still living w h o ever studied dinosaurs or their wotlds. I was included in t h e latter category, n o t because I study dinosaurs, but because I study h o w they died. Naturally, being a specialist on why everyone's beloved beasts are no longer on e a r t h makes o n e less t h a n popular. No wonder they scheduled my p r e s e n t a t i o n at t h e e n d of t h e last session. Nevertheless, I was happy to h a v e b e e n invited at all, and I a t t e n d e d many of t h e excellent talks. O n e I especially wanted to c a t c h was Erie Kauffman's; its subject was an update on h o w mosasaurs consumed a m m o n i t e s in those a n c i e n t Cretaceous oceans. T h e talks wete held in a large room packed with professionals and the general public. Erie strode to t h e p o d i u m at t h e appointed time and began speaking. Erie showed, on t h e basis of his decades of bite analyses (neatly 40 years h a d passed since his original paper with Kesling), how mosasaurs would stealthily creep up on t h e a m m o n i t e s and t h e n ( d e p e n d i n g on the particular species attacking or being a t t a c k e d ) , dive down, or swoop from behind, or pirouette in some mad dive-bomber attack, w h o o s h i n g through t h e watet, s n a t c h i n g their prey unawares, giving t h e m a "crack" and darned if they weren't suddenly calamari. In fact, Erie estimated t h a t at least a h u n d r e d specimens had b e e n s h o w n to carry u n d o u b t e d mosasaur t o o t h marks. Erie delivered a b r e a t h t a k i n g performance, and the rest of the audience clearly felt t h e same way. It was great: diving mosasaurs, dead a m m o n i t e s , predation

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in the J e e p dark Cretaceous seaways. At the end of the talk, Erie basked in the glow of the respectful questions. Bob Bakker c h i m e d in from t h e back of the room (as he is w o n t to d o ) , adding his imprimatur to t h e mosasaur bite mark theory. Bakker described h o w t h e peculiarly articulated mosasaur jaws allowed these great m a r i n e lizards to e n v e l o p t h e a m m o n i t e shells before piercing t h e m with t h a t mouthful of cruel, dagger-like teeth. O t h e r workers added their own anecdotes and stories about b i t t e n a m m o n i t e s they had seen. T h i s was paleontology at its finest, no doubt: serious research about an inherently interesting topic. Unfortunately, although t h e topic was good, the science wasn't. U n k n o w n to me at t h e time, in Seattle, S o p h i e Daniel, t h e eight-yearold daughter of a zoologist n a m e d T o m Daniel, was being s h o w n fossil exhibits at the local University of W a s h i n g t o n museum. O n e of t h e exhibits they viewed together consisted of a mosasaur skeleton encased with an a m monite bearing purported mosasaur " t o o t h marks." T h i s particular amm o n i t e was displayed in a case at about t h e eye level of Tom's daughter. S h e turned to her father ( w h o recounted t h e whole story to me later) and said, "How could there be t o o t h marks.' T h e shell would break in pieces and not leave t o o t h marks." H e r father looked at t h e specimen closely and had to agree with his daughter. In the question period following Erie's talk at Dinofest, I tried to make a similar point. In t h e past I had c o n d u c t e d simulated predatory attacks on nautilus shells, using pliers ( t o simulate t h e predator), and in every case t h e shell simply shattered. Imagine, I asked the group, trying to drive a nail through a nautilus shell (or an abalone or clam shell, for t h a t m a t t e r ) . Producing a large, circular hole in a mollusk shell by impact of a large, t o o t h shaped object is impossible. At this point t h e assembled audience (perhaps about 200 people) became somewhat confused and restless. W h o was this character from Seattle, not even a dinosaur paleontologist, d o u b t i n g our h e r o Bob Bakker as well as the mosasaur's ability to bite any number of t o o t h marks into a m m o n i t e shells? Hetesy! An uneasy rustling filled the room, and I sat d o w n in a hurry.

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Luckily for t h e h o n o r of t h e Mesozoic, Boh Bakker t h e n saved the day (if only temporarily) for t h e mosasaurs. He opined t h a t he had seen many such holes in a m m o n i t e s , obviously produced hy mosasaurs, and that although he respected my observations, he h a d an e x p l a n a t i o n t h a t might clear things up. Bob began his lecture from t h e back of t h e room: " T h e mosasaur jaw has long b e e n k n o w n to h a v e h a d a very peculiar articulation. T h e y could unhinge their jaws somewhat, in a m a n n e r analogous to most snakes, and position their jaws around t h e a m m o n i t e shell. T h e circular holes were p u n c h e d t h r o u g h t h e a m m o n i t e s shells, cookie cutter fashion, because t h e mosasaurs put pressure of t h e shell extremely slowly" W i t h this red herring now fouling t h e water, order was restored by N e i l Larson, a professional fossil collector w h o has probably found more a m m o n i t e s t h a n any other person in the world. Neil has found many a m m o n i t e s with t h e circular holes within t h e m and thus knows whereof he speaks, at least on any subject related to ammonites. He proposed t h a t h e , Erie, and Bob Bakker discuss the various specimens they had seen and report to t h e audience later in the day. T h i s pleased t h e group. As good as his word, later in t h e day Larson stood up to a n n o u n c e the results of this conference. After consulting with his colleagues, he could say t h a t t h e mosasaur t o o t h marks in a m m o n i t e shells were real. However, they could be confirmed in only three specimens in the world, rather t h a n in the h u n d r e d or more claimed earlier by Erie Kauffman. A n d t h a t is where matters left off as far as Dinofest went. But t h e affair certainly did not end there.

P u t t i n g a n i n t e r p r e t a t i o n t o t h e test U p o n my return to Seattle, T o m Daniel told me of his daughter's discovery, and I told h i m of t h e c o i n c i d e n t a l dustup at Dinofest. Tom laughed, especially w h e n I described Bob Bakker's theory t h a t a slow bite might produce holes where a rapid bite would n o t . Pressure is pressure, he declaimed, and t h e r e is no way a material such as mollusk shell could ever be b i t t e n so as to produce perfectly circular holes. T h e shell would crack, just as his daughter intuitively divined upon first seeing an a m m o n i t e shell with holes in it. 142

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Tom Daniel had a great advantage in this controversy, for he is a specialist in a field k n o w n as b i o m e c h a n i c s . Biomechanicists are really engineers dressed in zoologist or paleontologist clothing, for it is engineering principles that they bring to the work b e n c h . T h i s clan has d o n e m u c h work on the nature of molluscan shell and on h o w it responds to pressure. Typical molluscan shell is composed of several distinct layers and is far more t h a n a simple crystal substance. Tiny crystal of calcium carbonate are interlayered with tough organic material of t h e same composition as fingernail. T h e two together give far more strength t h a n either o n e alone. C o m b i n e d , they form what is k n o w n as a composite material. C o n c r e t e is a n o t h e r type of composite material; it is formed of lime, sand, and rock, w h i c h , w h e n c o m b i n e d , form a far stronger substance t h a n any of these materials alone. If you add in reinforcing steel rods to t h e mix, you approach (in design) a molluscan shell. O n e great advantage of molluscan shell over c o n c r e t e is t h a t it is capable of at least limited bending. Yet in m a n y ways, it also acts as porcelain c h i n a does: It reaches a certain critical p o i n t and t h e n shatters. Large cracks run through the material at high speed, usually producing irregularly shaped surfaces. P u n c h i n g holes in a mollusk's shell or a c h i n a plate c a n be d o n e only under very bizarre circumstances. Mosasaur t o o t h pressure does n o t seem to be o n e of t h e m . It seems very unlikely t h a t mosasaurs p u n c h e d holes in a m m o n i t e shells. W h y dwell on this story of what is n o w nearly four decades of interpretation about ammonites with holes in their shells as being caused by mosasaurs? Because paleontology has labored for so long under "stories" rather t h a n science. Erie Kauffman long ago found a shell with holes in it. He deduced t h a t the holes wete made by a m a r i n e lizard and t h e n , having c o m e to this c o n clusion, spun out a blow-by-blow tale to support it. N o t a single e x p e r i m e n t was ever performed. Tom Daniel, on t h e o t h e r h a n d , after having been alerted to this interesting problem by his young daughter, set out to see w h e t h e r various hypotheses would stand up to scrutiny. In doing so he employed the scientific method, perhaps the most powerful of all time machines. T o m convinced a grad student n a m e d Erica R o u x to try actually to produce round holes in nautilus shells (very close a p p r o x i m a t i o n s of a m m o n i t e shells) 143

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experimentally. T h i s e x p e r i m e n t was designed to d e t e r m i n e w h e t h e r the hypothesis t h a t a t o o t h could break a circular h o l e in a shell could be falsified (shown to be false). Etica constructed an artificial mosasaur jaw. It did n o t look m u c h like the real thing, being fabricated of metal with series of t e e t h made out of nails and screws, but nevertheless it closely approximated t h e real thing in many ways. T h e " t e e t h " descended o n t o t h e shell surface just as a mosasaur jaw would h a v e , and a gauge a t t a c h e d to t h e jaw showed t h e a m o u n t of pressure needed to produce a break. A nautilus shell was put between t h e jaws, and the type of damage inflicted on t h e shell was observed. For several days Tom Daniel's fourth-floot lab reverberated with cracks and snaps as shell after shell fell victim to these jaws of d e a t h . An army of mosasaurs could n o t have h a d so m u c h fun. A n d in all t h e carnage t h a t ensued, n o t o n c e was a round circular h o l e approximating t h e size of a mosasaur's t o o t h ever produced. All nautilus shells we h a d smashed up to this point had been empty. W h a t might be t h e effect of a living body in t h e shell? Might a circular hole be p u n c h e d in a shell filled with flesh? To test this possibility, Erica constructed nautilus "bodies" out of Jell-O and stuffed t h e m into the shell. O n c e again, t h e shells smashed gleefully, and larger circular holes the size of the t e e t h n e v e r formed (Smaller holes, never circular, did appear rarely in the walls of t h e shell in tegions underlain by t h e chambers.) A conclusion was reached: Unless a m m o n i t e shells were radically different from nautilus shells (which all investigators agree is n o t the case), t h e t e is no way that a mosasaur could h a v e produced a circular t o o t h h o l e in an a m m o n i t e shell. T h e mosasaut jaw produced in T o m Daniel's lab was constructed with a single i n t e n t i o n : to test w h e t h e r a circular hole could be p u n c h e d in a c h a m b e r e d cephalopod s h e l l — a n d thus to falsify (if possible) t h e hypothesis t h a t mosasaur t e e t h left circular t o o t h marks in a m m o n i t e shells more t h a n 65 million years ago. T h a t m e c h a n i c a l jaw was crude to look at, but it did its job. S o o n , howevet, a far more realistic test was made. T h e K a s e - J o h n s o n team was also intetested in actual tests, and they h a d access to far b e t t e t material. T h e Tyrell Museum has a large n u m b e r of beautifully preserved mosasaur skulls in its collections. Using molding and 144

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casting techniques, skilled t e c h n i c i a n s at t h e Tyrell created a hard-plastic cast of a large skull, t e e t h and all. N o t c o n t e n t merely to m u n c h nautilus shells, however, the masters of verisimilitude at t h e Tyrell did our experiments o n e (or several) better: T h e y took their mosasaur head to t h e Philippine Islands and tried it out on living nautiluses in t h e sea. I can only imagine t h e looks t h e Filipino customs agents must h a v e given this grotesque bit of carry-on luggage. A n d it is a good t h i n g t h a t t h e Society for the P r e v e n t i o n of Cruelty to A n i m a l s didn't get wind of this little gig. T h e chutzpah was amazing. A n d w h o came up with t h e m o n e y for this? In any event, off they went, and sure e n o u g h , mosasaurs could certainly break into shells, but making little cookie cutter holes in these shells was n o t in their a n c i e n t repertoire. W h a t can we say to end this story? I h a v e b e e n a bit unfair to Erie. Ironically, I think Erie Kauffman was right for t h e w t o n g reasons. Did mosasaurs eat ammonites? No current e v i d e n c e suggests t h a t they did. T h e bite story as originally devised, and t h e n latet a m e n d e d by Erie, is clearly implausible. But I h a p p e n to believe t h e mosasaurs did eat a m m o n i t e s . A m monites, aftet all, were a m o n g t h e most a b u n d a n t and c o m m o n l y e n c o u n tered food resources in t h e Cretaceous oceans. It is ahsutd n o t to assume t h a t large carnivorous vertebrates t h e n (as n o w ) relished c e p h a l o p o d meals. T h e elaborately o r n a m e n t e d a m m o n i t e shells, especially a m o n g larger species, were probably effective designs to thwart smaller predators, such as most fish. Mosasaurs, however, could h a v e b e e n highly efficient a m m o n i t e eaters. T h e only problem—for us paleontologists—is t h a t such attacks would never have left any sort of identifiable mark in t h e shells, o t h e r t h a n a few cracks. Such shells, after attack, would h a v e b e e n no more t h a n a few calcareous shards drifting to an uncertain fossilization at t h e b o t t o m of t h e sea. W h o would recognize such fossil fragments as t h e evidence of an a n c i e n t predatory attack ? Each spring, the eroding cliffs n o w seem to yield a new m a r i n e reptile from the black shale of Vancouver Island. S o o n e r or later, I am sure, o n e of these wondrous fossils will erode out of Sucia Island as well. It is certain t h a t mosasaurs great in size and n u m b e r o n c e r o a m e d t h e a n c i e n t seas of this 145

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region, a n d surely they would h a v e b e e n wonders to see. Now, sadly, they roam only in our i m a g i n a t i o n — a n d sometimes that imagination is stretched too far. Fossils c o m e d o w n to us t h r o u g h t h e immensity of geologic time. T h e y are our data. T h e y do n o t c h a n g e , but h o w we interpret t h e m does. It is we h u m a n s w h o h a v e to make t h e interpretations, and we are highly fallible time m a c h i n e s . T h e fossil record can be interpreted in myriad ways, and finding t h e t r u t h is no simple matter. T h e r e are a m m o n i t e shells with holes in t h e m , of t h a t we are sure. Of t h e rest, we c a n only subject hypotheses to tests t h a t will d e m o n s t r a t e t h e falsity of those t h a t are disproved. But whereas hypotheses can be s h o w n to be in error, they can never be proved true. T h a t is t h e n a t u r e of t h e time m a c h i n e we call the scientific m e t h o d . We c a n n o t be sure t h a t limpets drilled t h e telltale holes in ammonites. But we c a n be confident t h a t mosasaurs did n o t .

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H o w can we reconstruct t h e life of an e x t i n c t animal, such as an a n c i e n t ammonite? H o w is it t h a t paleontologists h a v e revivified dinosaurs as agile and obstreperous? H o w c a n they assert t h a t a pterodactyl could fly rather t h a n simply glide? T h e s e and m a n y more feats of apparent sorcery fill t h e scientific journals and sometimes spill over o n t o t h e wide screen and t h e wider popular consciousness. T h e y derive from a type of scientific analysis called functional morphology, w h i c h is a way of studying biological structures to determine not h o w they looked but h o w they worked and what they did. This form of analysis is a m o n g t h e most useful of time m a c h i n e s .

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Scientists w h o are interested in reconstructing t h e past lives of ancient organisms by studying form and function recognize three ptimaty factors that must be considered in interpreting biological sttuctutes. First, and most obvious, are t h e functional considerations: Just what does this structure do . 7

Most biological structures yield some obvious clue. Wings are clearly for flying, fins for swimming, legs for walking. But sometimes things get far more complicated. S o m e structures are not as we would imagine t h e m to be to fulfill some obvious function, whereas others share a function, or perform two or more tasks, a n d thus b e c o m e compromises in form. Take t h e gills of clams, for instance. Gills first evolved for respiration; they ate used to exttact oxygen from sea water. But in some clams, gills ate also used for feeding. T h e same structute n o w has two functions. It is optimal for n e i t h e r but, by doing b o t h jobs, serves its owners well. O t h e r structures seem i n c o m p l e t e , only partially useful, or so woefully inefficient as to be laughable. W h y do we h a v e appendixes and wisdom teeth, for instance? S o m e structures h a v e no obvious function at all. Intetpreting task, t h e n , is n o t e n o u g h to explain why some organs or biological structures h a v e t h e a n a t o m y t h a t they show. Yet evolution, which shapes all life, rarely produces wasted organs or structures. Perhaps more t h a n simple function is at work here. T h e second factor t h a t influences function is telated to constructional aspects. Organisms h a v e a very finite suite of material they can build with. T h e r e is no Teflon, or WD 40, or duct tape, or stainless steel, or a million o t h e r h u m a n - m a d e building materials in t h e animal and plant worlds. Some biological structures h a v e to be made of material less t h a n optimal for their function and are "designed" ( h a v e evolved) accordingly. O u r teeth, for instance. T h e y wear out, they are made of a mineral (apatite by n a m e ) that abrades a n d is attacked by decay over t h e years. W h y didn't we evolve stainless steel t e e t h , w h i c h would be far superior? T h e answer is obvious. O u r bodies can secrete the mineral apatite, but they c a n n o t produce steel. Finally, any biological structure must be viewed from a historical perspective. Evolution is like a river, and although it can eddy, t h e river even-

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tually flows in o n e d i r e c t i o n . S o m e structures or p r o t e i n s evolved by organisms early in their history stay w i t h t h e m t h r o u g h o u t t i m e and may play a large role in h o w they and their ancestors are e v e n t u a l l y m a d e . My favorite example of h o w historical factors affect t h e design of organisms comes from the study of t h e octopus. O c t o p u s e s are a m o n g t h e smartest creatures in t h e ocean ( m u c h more intelligent t h a n fish, for e x a m p l e ) , and o n e wonders why their brains did n o t c o n t i n u e to enlarge until they, like us, b e c a m e truly sentient creatures. Instead, they dwell in t h e n e t h e r world of semiconsciousness. In a classic a c c o u n t worked out by my friend M a r t i n Wells of Cambridge University, it was s h o w n t h a t t h e octopus suffers t h e ill effects of a choice made half a billion years earlier by its hoary c e p h a l o p o d ancestor, the first nautiloid. T h i s creature and its ilk evolved a copper-based rather t h a n an iron-based blood p i g m e n t to carry oxygen. Nautilus ( a n d h e n c e , we presume, t h e earliest nautiloids as well) is a quite stupid beast w i t h a very small brain. A copper-based blood p i g m e n t carries more t h a n e n o u g h oxygen to meet t h e needs of t h e n e r v e cells a n d b r a i n of a nautilus. However, copper c a n n o t carry as m u c h oxygen in blood as iron c a n . W i t h t h e evolution of a larger c e p h a l o p o d brain, oxygen availability b e c a m e an issue for the first time. Because of its large size, t h e poor octopus's brain is nearly always on the brink of oxygen starvation, for nerve cells above all others need a c o n s t a n t supply of oxygen. T h e octopus c a n n o t evolve a larger brain, because its blood supply will n o t support more nervous tissue. Worse yet, so basic is t h e type of blood p i g m e n t t h a t t h e c e p h a l o p o d s c a n n o t redress this wrong by evolving an iron-based p i g m e n t at this t i m e . It is too late. T h i s wrong choice offers an example of t h e historical aspect of functional morphology at work. T h e study of form and function is currently a growth industry in science. A l t h o u g h this type of study has a long history, t h e field has t a k e n on a rigorous d e m e a n o r only in t h e last three decades. In this interval, m o d e r n engineering techniques h a v e been employed in studying biological structures, and m u c h of this new emphasis stems from Duke University, where (among others) Professor S t e v e n W a i n r i g h t and his colleagues and students

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h a v e revolutionized t h e field. A considerable n u m b e r of paleontologists specialize in functional morphology. T h o s e practicing in this relatively new field often h a v e only sketchy evidence to work with; yet they are required to understand and synthesize—literally to "flesh out t h e bones"—in such a way as to bring e x t i n c t creatures to life. Yet functional morphology is n o t restricted to those w h o study t h e fossil record. T h e living as well as t h e long dead are scrutinized, and often it is an understanding of the living relatives of e x t i n c t animals t h a t makes possible a critical insight or breakthrough. Perhaps t h e most challenging functional interpretation occurs w h e n we address a creature t h a t has no living counterparts. Many of the Burgess Shale creatures of C a m b r i a n fame (found on a mountainside in British C o lumbia and vividly described by S t e p h e n Jay G o u l d in Wonderful Life) are in this category. T h e y often look like n o t h i n g still alive, and understanding the function of their peculiar bodies has taxed t h e imagination and skill of many scientists. Yet sooner or later, some insight is reached, and more often t h a n n o t t h e critical b r e a k t h r o u g h comes from two sources: a better understanding of similar bodies or body parts a m o n g the closest living forms (even if they are only distantly related) a n d analyses t h a t borrow from tool kits employed by engineers. In fact, t h e discipline of functional morphology is rapidly being co-opted by engineers w h o h a v e found t h a t studying animals is m u c h more fun t h a n building bridges! O n e of t h e great advantages of this type of work is t h a t several new approaches enable us to "revive" long-extinct animals with computer technology. We can make "virtual animals" by recreating t h e m on c o m p u t e r screens, using t h e same sorts of imaging and technology t h a t brought the dinosaurs of Jurassic Park back to life. Dinosaurs may be long dead, but we can study their c o m p u t e r images. We c a n often achieve new insights into their biology just by seeing t h e reconstructed animals on t h e screen. A n d there are even more powerful applications. Frequently, parts of a n c i e n t animals are reconstructed and t h e n subjected to various computer-simulated pressures, stresses, and strains—an imaginary animal e n c o u n t e r i n g imaginary forces. Yet the results are a n y t h i n g but imaginaty; they can lead to critical insights. Virtual modeling is a very powerful time m a c h i n e . 150

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The mystery of the ammonites In my own field, all of these elements h a v e recently coalesced to solve o n e of the longest-running mysteries in paleontology: W h y did a m m o n i t e s , whose closest living relative is t h e c h a m b e r e d nautilus, h a v e such complex sutures (the intersection of their chambers and shell walls) ? A n d why did these sutures,

"Virtual ammonites" created hy computer, with some of the data illustrating that increasingly complex sutures led to weaker shells.

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w h i c h often c a n be used like a fingerprint to identify an individual species, get more and more complex t h r o u g h time? T h e answers to this particulat problem came from an engineer. U n d e r s t a n d i n g a m m o n i t e s , perhaps t h e most c o m m o n and iconic of all Mesozoic invertebrates, really starts by studying submarines. A n d a horrible marine accident t h a t h a p p e n e d nearly 30 years ago focused m u c h a t t e n t i o n on h o w a m m o n i t e s m a y — o r may n o t — h a v e used their complex septa (the walls t h a t divide t h e shell into c h a m b e r s ) . On April 10, 1963, t h e U n i t e d States nuclear submarine Thresher exceeded a still-classified d e p t h and imploded, killing its 146 crew members in t h e process. Its remains sank to the b o t t o m of t h e A t l a n t i c O c e a n , at a depth of 8 5 0 0 feet about 100 miles east of C a p e C o d . T h e y rest there still, along with t h e remains of t h e crew, scattered over 4 0 0 square yards of muddy bott o m . T h e U n i t e d States Navy, using r e m o t e submersibles, visits this sad grave regularly to m o n i t o r t h e fate of t h e poisonous p l u t o n i u m and other radioactive waste n o w buried at this site. Four or five larger pieces c a n be observed: T h e sail, sonar d o m e , bow section, tail, and engineering sections are recognizable. T h e rest of t h e ship is represented only by scattered ftagments. T h e pictures t h a t emerge bespeak t h e violence of t h e implosion event itself and give m u t e but e l o q u e n t testimony to a law of submersibles: T h e r e exists a maximal d e p t h below w h i c h a submarine c a n n o t dive. If this d e p t h is exceeded, violent, catastrophic implosion ensues. A l m o s t 14 years to t h e day after t h e Thresher's hideous death, I anxiously watched a w i n c h do its slow work on t h e back of a Fij ian fishing boat sevetal miles off t h e verdant coast of Viti Levu, t h e largest island in t h e Fijian archipelago. T h e day before, I h a d caught eight healthy nautilus specimens, creatures at t h e time more precious (at least to a biologist) t h a n any gold or silver. I had n o t c o u n t e d on such a large haul and had decided to "bank" t h e m in a closed trap. T h e y had been caught at over 500 meters, which is about t h e greatest d e p t h at w h i c h these last members of a shelled cephalopod clan c a n reliably be caught, and they had been returned to that d e p t h . But this m o r n i n g my d e p t h sounder showed t h a t the trap I had lowered to 500 meters rested n o w at 750 meters instead. During the night, heavy 152

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surface waves had tugged at t h e buoy, dragging its tethered cage below to a greater depth on the steeply tilted sea b o t t o m . First visible only as a faint p a t c h of light in t h e deeper blue of t h e sea, the trap eventually m e t a m o r p h o s e d into a large c h i c k e n wire and rebar cube. But instead of the eight living nautiluses t h a t I had placed there for safekeeping, I could n o w see only shell fragments. W h e n we finally muscled the trap over t h e boat's side, t h e disaster was confirmed. Eight fleshy carcasses rolled lifelessly about on the b o t t o m of the trap, already m u c h scavenged by the countless smaller denizens of t h e sea. Yet it was t h e shells t h a t were of most interest; it was they t h a t told t h e tale. T h e y were smashed into n u m e r ous small pieces, as t h o u g h some malicious giant had whacked e a c h with a large hammer. T h e pieces were priceless: T h e y m a d e possible a detailed analysis of how pressure caused m e c h a n i c a l failure in a shelled cephalopod, for t h e nautilus and the Thresher had fallen victim to t h e same sad fate. Both had exceeded t h e greatest pressure t h a t their shell was designed to withstand. Implosion, a terrible end for a submarine, is t h e h a n d m a i d e n of hydrostatic pressure. T h i s inexorable force pushes against every square inch of any submerged vessel c o n t a i n i n g gas-filled spaces, and it increases with d e p t h . It is the force that causes ear pain in a swimming pool. It is t h e force t h a t killed the Thresher. S u c h a D a m o c l e a n sword is certainly noticed by the engineers w h o design submarines, and it has certainly b e e n noticed by nature's engineer, t h e principle of natural selection. It comes as no surprise t h a t most interpretations of a n c i e n t submarine d e s i g n — t h e form of t h e nautiluses and their close relatives, t h e e x t i n c t a m m o n i t e s — h a v e been viewed with this paramount fact in mind: Shell strength must be t h e primary c o n c e r n of every o n e of these a n c i e n t or m o d e r n diving devices. So I was taught by t h e greatest student of these creatures, Professor G e r d E. G. W e s t e r m a n n of M c M a s ter University in O n t a r i o , and until tecently I had no doubt about t h e veracity of this interpretation. N o w my mind has been c h a n g e d — a reversal brought about n o t by the study of any new fossil, living animal, or military submarine, but by experiments c o n d u c t e d by a n o t h e r investigator and his trusty Silicon Graphics workstation. T h e life of a n c i e n t a m m o n i t e s has been resurrected by t h e d e v e l o p m e n t of a virtual a m m o n i t e . 153

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since t h e Renaissance. In t h e 1600s, t h e British natutalist Robert H o o k e illustrated some of t h e copious a m m o n i t e fossils to be found at many localities a r o u n d his n a t i v e Britain a n d m a d e t h e first informed speculations about h o w they may h a v e lived. He n o t e d t h a t these a n c i e n t shellfish had shells p a r t i t i o n e d by m a n y calcareous walls ( t h e septa), w h i c h divided the shell i n t o individual c h a m b e r s . H o o k e correctly deduced t h a t the amm o n i t e s from his collections were closely related to t h e living c h a m b e r e d nautilus, k n o w n to h i m from shells brought from t h e far tropical Pacific Ocean. A m m o n i t e s a n d t h e nautilus b o t h live within a chambered shell, and t h e shell itself is cordoned off by t h e internal septa. It is thus reasonable to assume t h a t in many ways they shared a similar m o d e of life. But H o o k e recognized t h a t these two creatures differed in o n e great respect: T h e septa of t h e nautilus, n u m b e r i n g about 30 in an adult shell, h a v e a simple concave shape. T h e y are like small watch glasses fitted within the shell. A m m o n i t e s , on t h e o t h e r h a n d , exhibited vastly more elaborate septa. W h e r e a s their middles might be only slightly curved, t h e margins of t h e a m m o n i t e septa are crenulated into a complex series of curves and vaults t h a t intersect the shell as a very complex p a t t e r n . T h i s intersection is called t h e suture. In nautiluses, t h e suture describes a simple if slightly wavy line. In ammonites, the suture is a very complex c u r v e — a sine wave on LSD. H o o k e was most curious about h o w t h e nautilus and a m m o n i t e s might live. He t h o u g h t t h a t b o t h animals used their shelled portions as a buoyancy device and suggested t h a t the internal, c h a m b e r e d portions in b o t h were filled with air. But air at w h a t pressure? H o o k e was a genius, a person eclipsed in fame only by his immediate scientific a n t e c e d e n t in Britain, Sir Isaac N e w t o n . H o o k e asked t h e following question and, in so doing, set the stage for o n e of t h e most c o m m o n approaches in functional morphology: If this m e c h a n i s m functioned as he t h o u g h t , h o w could it best be engineered? Specifically, if some creature wished to h a v e a gas-filled shell to use as a buoyancy device, h o w could it most efficiently be built and most effectively work?

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T h e answer H o o k e arrived at was simple: T h e a m m o n i t e would h a v e a tiny gas gland capable of filling t h e c h a m b e r s with air at a pressure equal to t h a t of the surrounding water. W i t h such a system, t h e a m m o n i t e would be unlike a submarine: It could descend to any d e p t h and never worry about implosion, because its internal pressure would always m a t c h t h e external pressure, which increases by 14-7 pounds with every 33 feet of d e p t h descended. Hooke's supposition, t h a t a m m o n i t e s (and t h e nautilus as well) were capable of equalizing their internal gas pressure with t h e external pressure through the use of a gas gland, turned out to be false. Instead, these two groups of c h a m b e r e d cephalopods use (or used) a far less elegant solution: T h e i r internal parts are always at lower pressure t h a n a m b i e n t ( t h e water pressure of t h e d e p t h they inhabit at any given m o m e n t ) . In fact, studies have shown t h a t t h e c h a m b e r pressure is usually far lower. Nautiluses (and probably a m m o n i t e s ) are thus susceptible to implosion w h e n sufficient d e p t h is reached. T h e y therefore must depend on t h e strength of their shells to allow t h e m to descend to great d e p t h s in t h e sea.

Comparison of shell interiors from nautilus (right).

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and ammonite

Note the far greater complexity of ammonite septa.

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H o o k e was very m u c h a pioneer and a person of unimaginable brilliance. He was also very far ahead of his time, and he had set out a clear research program to investigate these animals further. Yet little more was written about ammonites for two centuries after Hooke's death, until these curious fossils called once more to scientists—this time as time markers, not biological curiosities. By t h e mid-1800s, a m m o n i t e s h a d t a k e n on e n o r m o u s importance to t h e scientific world, for, as we h a v e seen elsewhere in this book, they were early recognized as being t h e most useful of all fossils for subdividing sttata into time units. T h e pioneering biostratigraphical work of William S m i t h in England and D'Orbigny in France was carried out largely with collections of a m m o n i t e s . T h e s e coiled fossils were regarded literally as godsends, bits of m a t t e r placed on e a r t h by some convivial deity to h e l p us plodding h u m a n s figure out h o w old rocks are. Yet gradually, keener minds began to return to t h e biological questions first posed by H o o k e centuries before. T h e fossil amm o n i t e s were, after all, t h e remains of once-living creatures. H o w had these mysterious creatures lived, and above all, why had they produced such elaborate sutures? For reasons quite obscure, fossil cephalopods (which include ammonites) h a v e attracted some of t h e more colorful personalities ever to practice paleontology. Perhaps c o i n c i d e n c e , perhaps more, but no o t h e r area in paleontology is peopled by a more bizarre cast of characters t h a n the students of cephalopods, a n d especially those interested in a m m o n i t e s . Examples are n u m e r o u s and will be but briefly n o t e d (I want to keep some friends, aftet all). T h e late Rousseau Flower comes to mind, a garrulous sort w h o earlier in this century collected his cephalopod fossils garbed in cowboy outfit, including two C o l t pistols (he also a t t e n d e d a n a t i o n a l geological society meeting wearing a gorilla suit). T h e n t h e r e is t h e late Ulrich L e h m a n n , a mystic and astrologer (as well as an a m m o n i t e specialist) w h o consulted t h e stars in advance of research projects. A n d there's e v e n my close friend and colleague W. James Kennedy, w h o held a soiree a t t e n d e d by t h e president of Oxford University in h o n o r of t h e birthday of o n e of his pet guinea pigs. But for sheer eccentricity, few a m m o n i t e workers can m a t c h t h e n i n e t e e n t h - c e n t u r y British cleric and naturalist D e a n William Buckland. 156

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His gtave sits in a quiet glen n o t fat from Oxford, surrounded by the Jutassic a m m o n i t e - b e a t i n g exposures t h a t were his life's avocation. But Buckland was no mere paleontologist. He was an ordained minister and elder of t h e C h u r c h of England, and indeed he was devoutly religious. He was also clearly "certifiable," as my m o t h e r would say. Even more t h a n a c e n tury after his death, stories abound. Perhaps his most m e m o t a b l e act, performed while on a visit to the Natural History M u s e u m in Paris, was reaching into a bottle t h a t held t h e preserved h e a r t of Louis, t h e last King of France, snatching out t h e dripping organ, and taking a great bite from it, shouting, "I eat the heart of t h e King of France!" A h , nationalism. Lucky for Buckland the kingly heart was preserved in ethyl alcohol, rather t h a n in methyl alcohol or formalin. Early in life Buckland became fixated on two deities, G o d and amm o n i t e fossils, and he managed to mix t h e m together in producing a m e m o rable n i n e t e e n t h - c e n t u r y work k n o w n as The Bridgewater Treatise. Buckland thought he could prove t h e existence of G o d by showing t h e perfection of various aspects of nature, a m m o n i t e s included. He thus set out to illustrate how a m m o n i t e s may h a v e lived. The Bridgewater Treatise is of interest to m o d e r n a m m o n i t e workers because it presents the first detailed hypotheses on a m m o n i t e sutures since t h e time of H o o k e (and it far surpasses Hooke's interpretations in its detail). Buckland was obsessed with a m m o n i t e s during his life and saw thousands of specimens. He knew intimately t h e n a t u r e of t h e intricate suture marks lining the outer shell, and he pondered t h e i t m e a n i n g . His e x p l a n a t i o n for their presence was novel: He saw t h e m as buttressing structures put into t h e shell (by G o d ) to increase shell sttength. T h e more complex t h e suture ( t h e intersection of the c h a m b e r partition with t h e outer shell wall), t h e stronger the shell. T h i s e x p l a n a t i o n seemed obvious to Buckland. Just as a corrugated roof is stronger t h a n a flat sheet of metal would be, so too would corrugated a m m o n i t e septa be stronger t h a n simpler, flatter septa, such as those possessed by t h e nautilus. Buckland eventually went to meet his Maker, and his vast Bridgeii'ater Treatise remains a curious and somewhat derisive m o n u m e n t to one man's life. But a m o n g Buckland's theories, virtually all n o w dismissed 157

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or disproved, his c o m m e n t s on t h e function of a m m o n i t e septa in strengthe n i n g t h e shell stand shining apart. T h e y were largely accepted up to the present day.

D o e s m o r e c o m p l e x m e a n stronger? In t h e early 1900s new breed of paleontologist was emerging, investigators c o n c e r n e d n o t only with w h a t fossils could say about time but with what they could reveal about themselves and t h e world they lived in. T h e analysis of function began to be t a k e n seriously. Foremost a m o n g this new wave were G e r m a n s , most from t h e University t o w n of Tubingen. Tubingen already had a long association with paleontology, having been t h e h o m e of two of t h e greatest of all early paleontologists, A l b e r t Q u e n d s t e d t and his remarkable pupil, A l b e r t O p p e l . But these n i n e t e e n t h - c e n t u r y paleontologists were c o n c e r n e d with biostratigraphy, whereas their early twentieth-century descendants t h o u g h t more about m o d e of life, form, and function. Because they were surrounded by rocks rich in fossil a m m o n i t e s , it is no surprise that many of these students began to study a m m o n i t e paleobiology. O n e of t h e most brilliant of these students was A. Pfaff, w h o made the most detailed functional study of a m m o n i t e s up to t h a t time. He noted that a m m o n i t e s with compressed shells had more crenulations t h a n those with rounder shell cross sections. From this observation he deduced that the flatter shell regions were inherently weaker (because of their lack of curvature) and would therefore need more shell buttressing. R o u n d e r shells would be supported by the curvature of t h e shell and would require less buttressing— and thus less complex sututes. Pfaff and others of his time were also well aware of a n o t h e r curious facet of a m m o n i t e sutures: O v e r t h e long, 360-million-year history of the group, t h e septal sutures just seemed to keep getting more complicated. A m m o n i t e s d i d n ' t show a greater n u m b e r of sutures over t i m e — i n other words, their shells did n o t get packed with more and more s e p t a — b u t those septa t h a t were present b e c a m e more sinuous in theit appearance until, by the Cretaceous Period, they made the most complicated river course seem straight 158

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by comparison. ( S t e p h e n Jay G o u l d has disputed this long-held view in his recent book, Full House. G o u l d quotes t h e work of two paleontologists w h o used fractals to characterize the complexity of a m m o n i t e sutures and concluded t h a t this increasing complexity is less cleat-cut t h a n has b e e n supposed. T h i s may well be, for t h e r e are reversions toward simplicity in some lineages, most noticeably in a gtoup of C r e t a c e o u s a m m o n i t e s called t h e neoceratites. All in all, however, a pervasive trend toward increasing complexity clearly occurs in most evolving a m m o n i t e lineages.) In t h e 1930s a new paleontologist arrived at Tubingen, and his brilliance eclipsed e v e n t h a t of his illustrious predecessors. O t t o Schindewolf arrived at Tubingen as a young professor and proceeded to b e c o m e t h e most influential paleontologist of his generation. Schindewolf considered many large-scale questions, such as t h e nature of e v o l u t i o n and m u t a t i o n rate, t h e cause of mass extinctions, and, of course (like all good G e r m a n paleontologists), the curious evolution and p a t t e r n of a m m o n i t e sutures. Schindewolf was so gifted that he n o t only attracted G e r m a n students but also drew young paleontologists to his labs and lecture halls from across t h e seas. T h e s e disciples included young G e o t g e Gaylord Simpson, an A m e r i c a n paleontologist who was to reach the top of his profession as well. Schindewolf kept t e a c h i n g and c o n d u c t i n g research e v e n during World War II, and soon thereafter a succession of o u t s t a n d i n g a m m o n i t e workers were graduated from Tubingen, including D o l p h Seilacher, Jost W i e d m a n n , Jurgen Kullman, and t h e m a n whose n a m e was to b e c o m e synonymous with the functional morphology of a m m o n i t e s a n d t h e i t complex suture, Gerd W e s t e r m a n n . T h a n k s to a providential attack of jaundice, W e s t e r m a n n just missed being sent to the eastern front as a boy soldier. S o o n after t h e wat, he was conscripted by t h e victorious allies as a coal miner, but he soon escaped t h a t fate and completed his P h . D . under Schindewolf's supervision. W i t h degree in h a n d he immigrated to C a n a d a , where he received a university post in t h e early 1960s. W e s t e r m a n n quickly rose t h r o u g h t h e professorial ranks at his college, McMaster University in H a m i l t o n , O n t a r i o . M u c h of his early work was on the biostratigtaphy of Jurassic a m m o n i t e s , a n d like all good G e r m a n 159

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paleontologists, he compiled and published massive monographic treatm e n t s on his specialty. But unlike many of his colleagues, W e s t e r m a n n began to wonder n o t only when his fossils lived but also how they lived. He began to delve deeply into t h e structures and possible workings of these most enigmatic of fossil invertebrates. In 1971 W e s t e r m a n n published a landmark and revolutionary paper about a m m o n i t e paleobiology. By incorporating newly available information about t h e function of t h e nautilus shell based on breakthrough work conducted by Eric D e n t o n and J o h n G i l p i n - B r o w n in t h e mid-1960s, Westerm a n n proposed t h a t t h e relative h a b i t a t i o n d e p t h of any a m m o n i t e could be d e t e r m i n e d by a simple m e a s u r e m e n t of two parameters found within every a m m o n i t e shell. A l t h o u g h t h e m e t h o d did n o t reveal t h e actual measured depth at w h i c h a given species of a m m o n i t e resided, it yielded t h e relative d e p t h s of various a m m o n i t e taxa: t h a t species A was capable of inhabiting deeper water t h a n species B, and t h a t B lived deeper t h a n C, and so on. A corollary to this discovery was t h a t those a m m o n i t e s with the most complex sutures generally showed t h e deepest d e p t h ranges. All of t h e paleontologists back to Buckland seemed vindicated. A m m o n i t e s with complex sutures lived deeper t h a n those with simpler sutures. During t h e 1970s W e s t e r m a n n kept making discoveries t h a t painted a whole new picture of h o w these a n c i e n t creatures lived and "worked." He used innovations, employed a variety of engineering techniques, and in pioneering fashion e v e n co-authored a paper with a m e m b e r of t h e engineering faculty at his university. O n e of his findings was t h a t a m m o n i t e s with highly complex septa h a d t h i n n e r septa t h a n those with simpler morphologies— and far t h i n n e r septa t h a n any of t h e nautiloids, t h e supposedly most primitive forms w i t h t h e simplest septa of all, watch-glass-like structures slung b e t w e e n t h e shell walls. T h e r e was only o n e snag in all of this: Nautilus, with t h e simplest of septa, managed to live in very deep water. Nevertheless, a general model seemed to be emerging. A m m o n i t e s evolved ever more complex septa t h a t were t h i n n e r t h a n those with less complex morphologies. Simple but strong septa would h a v e to be very thick, and making thick septa

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"cost" t h e animals in t h a t they h a d to e x p e n d more m e t a b o l i c energy. An alternative was to m a k e t h i n septa but septa so complex t h a t they were stronger, t h a n thick septa of lesser complexity. I was privileged to be a grad s t u d e n t of Gerd's at t h e time he was making these seminal discoveries. His office was always open, and we often talked of a m m o n i t e s and many o t h e r things. W h y would they h a v e produced such complex septa? C o u l d some o t h e r function h a v e b e e n involved? Might the very complexity s o m e h o w h a v e been used for a secondary function, such as some type of respiration, or muscle a t t a c h m e n t , or e v e n t h e removal of liquid from newly forming chambers? W e s t e r m a n n would mull these possibilities over and t h e n reject t h e m . Structural support seemed t h e only possibility. T h e intricacies of a m m o n i t e septa continued to intrigue paleontologists during the 1970s and 1980s, but Gerd W e s t e r m a n n was king. Refinements to the model of septa as structural support were made, and W e s t e r m a n n , in collaboration with a brilliant post-doctoral student named Roger Hewitt, began using ever more sophisticated engineering techniques to study these forms. O n e generalization reigned: A m m o n i t e s with more complex septa were capable of living at greater depths in greater pressures. It was a story of imperialist evolution: ammonites invading ever deeper waters through time, colonizing regions of the sea that were previously too deep for their shells. O n e could envision legions of new a m m o n i t e food succumbing to the first prey—their shells, and depth, no longer protecting t h e m from these efficient Mesozoic predators. From Buckland to W e s t e r m a n n was over a century, a long time in science. A m m o n i t e s were touted as engineering marvels, m i n i a t u r e submarines with shells designed to withstand t h e o c e a n depths. Evolution, t h a t supreme engineer, even kept improving t h e design by creating ever more complex septa. W h o could disagree? T h e first crack in t h e edifice of this wonderful p a l e o n t o l o g i c a l story came in 1994, a n d it c a m e from Bruce S a u n d e r s of Bryn M a w r C o l l e g e . Saunders is a specialist in Paleozoic a m m o n i t e s , w h i c h lived from t h e i r inc e p t i o n i n t h e D e v o n i a n Period, some 4 0 0 m i l l i o n years ago, u n t i l t h e e n d

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of t h e Permian Period, some 250 million years ago. T h e a m m o n i t e s of this time possessed relatively simple septa and sutures, hut they did show a progressive increase in complexity from the earliest to t h e latest. Saunders, who was interested in t h e shapes of these many early a m m o n i t e s , conducted an extensive study of many taxa. He amassed a large collection and t h e n proceeded to cut e a c h of these specimens (some priceless, most n o t ) in half with a d i a m o n d saw. T h e perfectly bisected fossils could t h e n be easily measured for t h e i t shell shape. At t h e same time, Saundets decided to measure the thickness of their septa, because these wete visible, and because no o n e had yet repeated W e s t e r m a n n ' s e x p e r i m e n t s in correlating septal thickness with septal complexity ( w h i c h h a d b e e n c o n d u c t e d only on Mesozoic amm o n i t e s ) . In t h e Mesozoic specimens he studied, W e s t e r m a n n had found t h a t t h e a m m o n i t e s with t h e most complex septa were also those with the t h i n n e s t . To his surprise, Saunders found no such relationship in his Paleozoic a m m o n o i d s . It was clear to Saunders t h a t s o m e t h i n g was amiss. Coincidentally, I was visiting Saunders in his Bryn Mawr lah soon after he made this discovery, a n d we talked about t h e implications. I agreed with him: If more elaborate septa were not t h i n n e r t h a n those of lower complexity, what was the use of going to all t h e trouble of elaboration—unless this particular form was serving some o t h e r function. But what? Perplexed, we did what most people do w h e n facing a problem. We sought help. H e l p in this case c a m e from T o m Daniel of t h e Zoology D e p a r t m e n t at t h e University of W a s h i n g t o n , w h o m I knew slightly at the time (we met h i m in C h a p t e r 6 on mosasaurs). He had c o m e from t h e c e n t e r of functional morphology at D u k e Univetsity, where he had been a Steve Wainright student. T o m had started as an engineer and t h e n switched to zoology. He was thus ideally trained to interpret form and function. He worked in a cramped lah packed with wires, machines, microscopes, computers of all makes, and students. Especially students. Students of all shapes, forms, and levels. G r a d u a t e students and post-docs, undergrads and scientific visitors. T o m was n o t yet forty, yet he had alteady received the University's O u t s t a n d i n g Teaching Award, as well as h a v i n g distinguished 162

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himself in a slew of scientific papers. He was a m a g n e t for those w h o wanted to learn about how animals wotk. W a l k i n g into Tom's lab was like walking into a hurricane: noisy, energizing, exhilarating, c h a o t i c . T h e m a n himself was perched in an alcove piled with papers and electronics. Fueled by sugar, caffeine, a n d cigarettes, he barely t o u c h e d t h e floor while walking. Tranquility was n o t part of this package. H u m o t was. T h e lab ran on laughter and tespect. It e m a n a t e d good feeling, and it genetated good science. " W h a t can I do for you two boys?" S u c h was our i n t r o d u c t i o n to T o m Daniel.

Virtual a m m o n i t e s We had brought several a m m o n i t e specimens for T o m to peruse. We explained t h a t the complex septa h a d for centuries b e e n considered structural supports but t h a t we h a d our doubts. W h a t did he think? T o m spent several minutes turning over t h e specimens, looking at t h e septa, m u t t e r i n g to h i m self, singing songs, and trying out various accents. T h e n he p r o n o u n c e d , "Well, they certainly weren't used for s t r e n g t h e n i n g t h e shell." T h u s began a 4-year collaboration t h a t c o n t i n u e s still. Saunders and I c o n v i n c e d T o m Daniel t h a t the " a m m o n i t e suture problem" was important. Perhaps to h u m o r us, or perhaps because he saw t h e beauty and mystery in such complexity, T o m decided to take on this problem, but in an interesting fashion. He decided to test those aspects of shell sttength that wete related to sutural complexity n o t on actual specimens, and n o t even on models made of some bioplastic or o t h e r casting material. He decided to build what we would eventually call "virtual a m m o n i t e s " on computers. A year or so before our arrival with fossils in h a n d , T o m Daniel had been awarded a grant for equipping his d e p a r t m e n t with Silicon Graphics workstations. T h e year before, these computers h a d gained instant notoriety when they were used by t h e creators of Spielberg's Jurassic Park to bring t h e film's stars—the dinosaurs—to life. Tom's acquisition of so many of these 163

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workstations h a d made his c o m p u t i n g c e n t e r t h e rival of small software corporations. Even more impressive, Tom actually knew how to use t h e m . But h o w to test t h e strength of an a m m o n i t e ? H o w to test the hypothesis t h a t increasing septal complexity made t h e shell stronger? O n e could make exact molds. But t h a t would require many weeks of skilled artisan work, and e v e n t h e n it would be impossible to d e t e r m i n e w h e t h e r the artificial a m m o n i t e s were responding to pressure in way faithful to the original— w h e t h e r t h e artificial shell was actually of even strength and was failing because of material rather a n t i q u e design properties. Test an actual specimen? As beautiful as many a m m o n i t e fossil are, it is doubtful t h a t any have survived t h e m i n i m u m of 65 million years e n t o m b e d in sediment since their last demise w i t h o u t undergoing mineral changes t h a t would compromise the delicate balance of shell strength. T h e s e intractable problems had stymied all past investigators. T o m Daniel proposed taking a new tack: Build the amm o n i t e on t h e computer, and t h e n subject it to simulated pressure. Just before our c h a n c e arrival (a visit rued by all at times over the next 4 years), Daniel had bought t h e site license for a new generation of engineering software program. O n e of the most powerful of all engineering procedures is called finite e l e m e n t analysis, or FEA. FEA works by subdividing complex structures into small e l e m e n t s and t h e n m o n i t o r i n g forces t h a t act at t h e junctures, or nodes, of e a c h of these elements. It thus embodies the t i m e - h o n o r e d m e t h o d of attacking a large and difficult problem o n e small step a t i m e . A n y structure is b r o k e n up into thousands of tiny regions, and t h e stress acting on e a c h region is e x a m i n e d separately. A m a p can t h e n be d r a w n to show h o w forces acting on t h e entire structure are encountered. FEA had long been the province of those blessed with large mainframe computers. But t h e computer revolution of the past decade had packed computing power into very small boxes. T h e Silicon Graphics workstation had the processor and e n o u g h memory to construct a charging Tyrannosaurus rex—or to build an a m m o n i t e shell, n o d e by n o d e , and t h e n subject it to pressure. A n d so we began building a m m o n i t e s by computer. Tom's first efforts were crude, but just as evolution starts simply and builds up, so too did the virtual a m m o n i t e s b e c o m e more and more elegant. A n d e v e n our early ef164

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forts yielded fascinating results: As t h e septa in t h e virtual a m m o n i t e s became more complex, t h e stresses applied to t h e m b e c a m e more catastrophic. O u r first runs examined simple cup-shaped septa a n d t h e n septa with folds and kinks that looked vety m u c h like t h e septa of early a m m o n i t e s . T h e simple cap-shaped septa proved far more resistant to stress; this was t h e insight that had led Tom, on our first meeting, to suggest t h a t a m m o n i t e septa had not evolved primarily because they afforded s t t e n g t h against implosion. T h i s was clearly not t h e scenario t h a t a m m o n i t e paleontologists envisioned. T h e evolution of m o t e complex septa was supposed to m a k e t h e shells stronger, not weaker. Perhaps it was the methodology? W e r e we forgetting something? We went back to the drawing board. Bruce Saunders and I were sent to our collections, where we sectioned a m m o n i t e s and made exacting measurements of the thickness of wall and septa, for we needed to e n t e r these values into the c o m p u t a t i o n models if any sort of relationship with reality was to be achieved. In the process we learned m u c h about t h e average thickness of real ammonites, and all this information was fed into t h e models. Weeks turned to m o n t h s , and m o n t h s to years, as T o m and his grad student Btian H e l m u t h , w h o had joined t h e project, produced ever more elaborate ammonites. C o m p u t a t i o n a l time soared. We were n o w r u n n i n g terabits of computations, and eventually eleven Silicon G r a p h i c s m a c h i n e s were r u n n i n g simultaneously, days at a time, for each run required an h o u r and yielded just a single data point. O v e r time, t h e simulations wete made not just on septa but on shells with septa within; the results as they flashed up on the screen were hauntingly beautiful. T h e images showed t h e distribution of stresses as colors, and t h e a m m o n i t e s would light up as spectacles of sparkling reds and yellows, blues and greens d a n c i n g across septal j u n c t i o n s and shell wall. By late 1996 an e n t i t e school of a m m o n i t e s lived in t h e basement of Kincaid Hall, populating t h e bowels of t h e building rather t h a n t h e ocean deeps. T h e m a c h i n e s n o w ran simultaneously, and Brian H e l m u t h ran between t h e m for all t h e hours of many days, plucking a n e w n u m b e r from each laborious, hour-long c o m p u t a t i o n . As T. rexes lived and died in the California studios making Jurassic Park, t h e b r e t h r e n of these powerful machines raised a m m o n i t e s from a n o t h e r grave in Seattle. 165

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All this effort required money. G r a d students d o n ' t c o m e free, and computer time costs. Early in our efforts, we sent a proposal to the N a t i o n a l Science F o u n d a t i o n soliciting a modest grant to fund our study. S u c h grants are peer-reviewed; about a dozen colleagues read each proposal (a document about fifteen pages long) and rate it anywhere from Excellent to Poor on the basis of the merit of t h e proposal, its significance, its practicality, and the qualifications of t h e proposers. T h e s e grants are a bear to get—only about 1 5 % are funded in any given year—so t h e c o m p e t i t i o n is fierce. We submitted out proposal with high hopes, because we h a d demonstrated (we t h o u g h t ) t h e feasibility of our research program. O u t went the grant, and six m o n t h s later it came back, rejected. T h e reviews were split. A b o u t half of our judges were absolutely ecstatic at this new approach to an old problem. T h e o t h e r half were equally certain t h a t we were completely off base, that it could never work, and t h a t everybody knew what a m m o n i t e septa were for anyway. T h e low ratings d o o m e d t h e proposal. Rejection in h a n d , we rewrote t h e proposal. A n o t h e r six m o n t h s went by, and m e a n w h i l e t h e c o m p u t e r c h u r n e d out numbers. A g a i n a p h o n e call, again a rejection. But t h e section head at t h e agency within t h e N a t i o n a l Science F o u n d a t i o n to w h i c h we were submitting, a paleontologist named C h r i s Maples, saw merit in our approach, and threw in a small, one-year allowance t h a t kept our m a c h i n e s rolling. He told us, however, t h a t the amm o n i t e workers of t h e world seemed u n a n i m o u s in their c o n d e m n a t i o n . Leading this charge was n o n e o t h e r t h a n my research supervisor from McMaster University, G e r d W e s t e r m a n n . In several apoplectic p h o n e calls and letters, he let me k n o w t h a t I must h a v e gone mad or suddenly stupid. As t h e model matured, we were able to ask new things. We built in septa of many types and designs, and we varied shell wall thickness and septal thickness as well as septal c o m p l i c a t i o n and design. We varied the spacing of t h e septa. Eventually we were able to subject t h e computer models to attack by virtual predators and to vary t h e simulated attacks. More time crept by; Tom's two infant daughters became little girls; Tom quit smoking. A n d t h e n in t h e spring of 1996, t h e most wonderful thing happened: Tom received a p h o n e call a n n o u n c i n g t h a t he had been chosen to receive a 166

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M c A r t h u r Award, o n e of t h e so-called genius grants. T h e a m m o n i t e work gained new credibility. By early 1997 we had e n o u g h n u m b e r s to produce a solid papet stating what we now know: A m m o n i t e septa did get more complicated t h r o u g h time, but t h a t complication had n o t h i n g to do with h a b i t a t i o n in ever greater d e p t h . Ironically, t h e eatliest of all septa designs, t h a t used in t h e Paleozoic Era of 500 million years ago by t h e earliest nautiloid cephalopods (and a plan close to t h e design used today by t h e still-living nautilus), is by far the best design for shell strength. But a m m o n i t e s , t h r o u g h o u t their history, had freely a b a n d o n e d t h a t design. W h y ? After all of this time and effort we knew what a m m o n i t e septa did not do, but we still d i d n ' t k n o w w h a t they did accomplish with their amazing complexity. O u r best guess about t h e real function of a m m o n i t e septa comes from studying the still-living nautilus. T h e nautilus achieves nearly prefect neuttal buoyancy in the ocean with its chambered shell. As t h e animal grows, it secretes new chambers, and in these lie pools of liquid that must be removed. I have long thought that t h e tate at which this liquid is removed is the ultimate rate-limiting step in t h e growth of a nautilus, as well as in t h a t of an a m m o n i t e . But a new possibility has been entertained in the 1990s: Perhaps it is n o t the tate at which a c h a m b e t is emptied but rather the rate at which it can be refilled. T h e buoyancy system in these creatures—the e x t a n t as well as the extinct—is a two-way street. N o t only can a c h a m b e r e d cephalopod get lighter in the sea (and thus reduce its buoyancy), but it c a n also get heavier, by readmitting liquid into previously emptied chambers. W h y do this? T h a t answer is simple. T h e Achilles heel of the shelled cephalopod design is t h e fact that any removal of shell at its a p e r t u r e — t h r o u g h shell bteakage by accidental contact or, more frequently, by predatory a t t a c k — m a k e s the cephalopod suddenly mote buoyant. T h i s is probably t h e most dangerous thing that can h a p p e n to one of these creatures. W h e n suddenly made buoyant through shell loss, a chambered cephalopod loses its freedom of m o v e m e n t . Sudden buoyancy causes it to float to the surface of t h e sea, where it is t h e helpless victim not only of creatures in the sea but of creatures in the air as well, t h e ubiquitous birds watchfully waiting for any type of food to emerge from the depths. 167

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S u d d e n loss of buoyancy is certainly fatal to a nautilus. In most places where it lives, t h e surface of t h e sea is simply too warm for a nautilus to live. Surely,

t h e r e must be n u m e r o u s a d a p t a t i o n s — s u c h as rapid chamber

refilling—to c o m p e n s a t e for this hazard. But t h e r e are not! T h e rate of refilling in a nautilus is very slow. A n d t h a t characteristic, which I discovered in t h e mid 1980s, may be a clue to why a m m o n i t e s evolved more complicated sutures. T o m Daniel has looked at this problem and has concluded that the complications of septa w i t h i n t h e c h a m b e r e d cephalopod shell would favor t h e readmittance of water to an already emptied chamber. Because of surface tension properties, such complications actually make it easier for an amm o n i t e to refill chambers. Because any bite by a predator would cause a sudd e n increase in buoyancy, this type of a d a p t a t i o n would be selected for. It is a simple a n d elegant solution. A m m o n i t e s with more complicated sututes would be better able to refill c h a m b e r s rapidly—and thus become less buoyant—following a predatory attack. As ever more predators evolved in t h e Mesozoic world, including a whole army of n e w types of shell-breaking predators, a m m o n i t e s "retaliated" by evolving ever more elegant and sophisticated ways of c o m p e n s a t i n g for sudden buoyancy. If our view is correct, t h a t m e a n t more complicated sutures. Microcomputers h a v e thus transported us back into Mesozoic oceans. T h e y h a v e served as powerful time m a c h i n e s . W h e r e are they now, these elegant ammonites? Could n o t a few, at least, still grace our planet? Sadly, I k n o w t h e answer to t h a t question. T h e y are gone, long gone, never to be resurrected, driven into e x t i n c t i o n by the collision of a giant c o m e t with t h e e a r t h 65 million years ago. But some vestige of t h e m persists in t h e fertile imaginations of a few paleontologists, for surely I am n o t alone in c o n t e m p l a t i n g deep, calm bottoms where these ancient creatures evolved structures whose startling regularity and grace so long h a u n t e d my dreams.

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ago, w h e n animals had but a single c o m m o n n a m e , natural philoso-

phers speculated about t h e separateness of animals and plants. Surely t h e individuality of what we n o w recognize as species (as well as t h e richness and diversity of these entities) was there for any to see. But just as surely there were connections between certain organisms. Dogs are n o t wolves, and lions are n o t lynx, yet w h o would deny t h a t some c o n n e c t i o n exists? But h o w much, and why? If life is a great tree, h o w ate its b t a n c h e s differentiated, and how can those p t u n e d by e x t i n c t i o n be detected?

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T h e c l a s s i f i c a t i o n o f life We k n o w so m u c h more now. We k n o w about evolution, and genetics, and the double helix of life uniting all living organisms on this planet. Yet there is speculation and mystery still about t h e categories into which we classify life ( t h e province t h e field of study k n o w n as t a x o n o m y ) , their validity, and t h e relationships a m o n g t h e m ( t h e province of systematics). We know that life is organized into basic units, the species, and t h a t species somehow come into being, exist for a period of time, and t h e n disappear t h r o u g h extinction. Species were o n c e recognizable only for their morphology and t h e n , as life scientists peered closer, t h r o u g h t h e recognition t h a t species are entities that c a n successfully interbreed. Finally, as technology advanced m u c h further, scientists delved into t h e very D N A of a species, to discover t h e nature of the unique aspects of t h e g e n o m e t h a t dictate t h e n a t u r e of all o t h e r characteristics, be they physical or behavioral. Defining species n o w dead is m u c h harder. T h e r e is no D N A to play with, no opportunity to observe breeding habits. Assigning fossils to species groups is thus m u c h more difficult t h a n categorizing living creatures. Yet is it d o n e — w i t h mistakes to be sure—but d o n e nevertheless, probably with good success. It is in t h e nature of our species to categorize things, to classify; and fossils are no exception. M a n y species still living h a v e left no fossils; usually these are t h e creatures with no skeletal or o t h e r hard parts t h a t might readily fossilize. C o n versely, many fossil species h a v e no living relatives; such victims of extinction h a v e left no kin, and these poor o r p h a n s are often left dangling in our classification schemes. But a good many animals and plants on earth today do h a v e a fossil record, a n d it is from these organisms t h a t we can learn the most about evolution. No paleontologist is i m m u n e to t h e call of evolutionary study. Even we stratigraphic paleontologists, w h o c o m b t h e rock record for adequate time markers, quickly h e a r t h e siren song of evolutionary c h a n g e as we dig fossils from rocks. A n d t h e n e x t natural step for any scientist is to write about it, the evidence of e v o l u t i o n — t o describe, to study it. T h a t is what we do. It is 170

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certainly no burden, and is usually a pleasure, to make such studies. T h e fossils of Sucia are an example. A m m o n i t e s are the greatest fossil treasures to c o m e from Sucia. Yet here and there o n e c a n discover fossils easily mistaken fot a m m o n i t e s , until one looks a bit closer and sees t h a t these particular shells are simpler, less elegant. T h e i r c h a m b e r edges form simple wavy lines, rather t h a n t h e flowery contacts so characteristic of t h e a m m o n i t e design. T h e y are fossils of nautiloid c e p h a l o p o d s — a group represented today by the c h a m b e t e d n a u t i l u s — cousins of t h e a m m o n i t e s . A l t h o u g h the nautilus has b e e n studied for centuries, many questions about it remain unanswered. Is t h e nautilus a very a n c i e n t creature or a very new one? Is it a living fossil (a designation first proposed by C h a r l e s Darwin for organisms with long fossil records bereft of evolutionary c h a n g e ) ? Is it t h e last of its kind or o n e of t h e first? Does it h a v e many relatives or very few? A n d perhaps most important, why should a n y o n e care about these odd animals? For me, at least, t h e h o o k is t h a t this e n d a n g e r e d body plan, so rare among swimming animals in today's seas, was o n c e clearly t h e rule, n o t t h e exception. T h e nautilus has two great claims to fame. First, because its shell so closely resembles t h a t of t h e a m m o n i t e s , it c a n be used to understand b e t t e t the complex workings of t h e intricate a m m o n i t e shell, w h i c h must h a v e evolved as a compromise b e t w e e n p r o t e c t i o n and a form of buoyancy control. Studying still-living creatures as a m e a n s of understanding t h e past is one of the most powerful of all time m a c h i n e s , and in this case, t h e nautilus seems to give us an accurate glimpse far back into time. Second, as I h o p e to show in this chapter, t h e nautilus does appear to be a living fossil, a form t h a t has existed for millions or e v e n tens of millions of years without change. We h a v e discoveted t h a t some fossil nautiloids closely resemble the living species. T h i s realization has c o m e about only because detailed studies of the nautiloids show t h e evolutionary relationships of the distinct species. T h e classification a n d systematic zoology of the nautiloids have enabled us to identify t h e m as living fossils. T h e way in w h i c h we study the evolution of animals and p l a n t s — i n c l u d i n g t h e nautiloid 171

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cephalopods—is t h r o u g h t h e disciplines of systematics and taxonomy. C o m bined, they are a n o t h e r powerful type of time m a c h i n e . T h e story of h o w t h e nautilus has b e e n classified is an example of how these particular time m a c h i n e s operate. It is detective work, and as t h e work progresses a n d t h e family tree is discerned, o n e feels great satisfaction, fot any view of a family tree always brings new knowledge and a new perspective on t h e past. Imagine t h a t you did h a v e access to a time m a c h i n e capable of whisking you (along with a good set of scuba gear) back to t h e last days of the Mesozoic E t a — t o 65 million years ago, just before t h e asteroid strike that was to end t h e A g e of Dinosaurs. W h a t would you see? On land, of course, you would sooner or later e n c o u n t e r dinosaurs in great variety and profusion. But in the sea, would it be as immediately apparent t h a t you were not in our time, t h a t you were indeed back in t h e Mesozoic Era? Actually, as you settled o n t o a C r e t a c e o u s sea b o t t o m 50 feet deep, it might be e v e n more apparent t h a t you h a d arrived in a foreign, long-ago place, for in any Cretaceous ocean you would quickly e n c o u n t e r a fantastic assemblage of large, alien-looking shelled c e p h a l o p o d mollusks acting and swimming like fish. By the Mesozoic Era, t h e c h a m b e r e d cephalopods were already a n c i e n t . As t h e first latge, swimming carnivores in t h e world's oceans, they h a v e b e e n a m o n g the domin a n t marine predators for m u c h of t h e last 500 million years; there are over 10,000 k n o w n fossil species. R a n g i n g in shell size from less t h a n an inch to m o t e t h a n 12 feet across, and in shape from coiled to straight to elabotate, c a n d y - c a n e c o n t r a p t i o n s , t h e great armored dreadnoughts of the Mesozoic world t h a t you would see would be of two kinds: a m m o n i t e s and nautiloids. T h e former, by far t h e more a b u n d a n t and diverse of the two groups, would be easily distinguishable by their more o r n a t e shells and peculiar shapes. But t h e latter, more conservative group, bereft of t h e rococo ribs and spines, keels, and knobs t h a t characterize t h e a m m o n i t e lineage, would look quite familiar to most of us. W h o has n o t seen t h e shell of the nautilus? Following t h e 6 5 - m i l l i o n - y e a r - o l d C h i c x u l u b c o m e t impact (the " K / T " e x t i n c t i o n ) , all of t h e a m m o n i t e s (like t h e dinosaurs on land) were quickly e x t e r m i n a t e d . Yet t h e r e were nautiloids t h a t survived this great 172

A) Exterior and B) interior views of the Chambered Nautilus. (With permission of Scientific American.)

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global catastrophe. But w h i c h ones, and h o w many? Was it some distant ancestor of our familiar c h a m b e r e d nautilus (technically Nautilus pompilius)! Or was it t h e very same species t h a t is living today, whose shells can be purchased in any curio or shell shop? A n d did only a single nautiloid survive, or might several types (either several species or higher t a x o n o m i c groupings, such as several genera or e v e n several families) h a v e dodged the bullet of this mass e x t i n c t i o n ? Even several years ago, paleontologists w h o study the fossil record of shelled cephalopods ( w h i c h include t h e a m m o n i t e s and nautiloids) would h a v e told you t h a t t h e nautiloid cephalopods living in the Cretaceous were only distant ancestors of t h e Nautilus of our world, in the same way that early apes are related to h u m a n s . According to this evolutionary hypothesis, the single genus Nautilus, with its four or five living species, is the sole surviving r e m n a n t of this ancient group. Increasingly, however, this time-honored view of cephalopod evolution appears to be a hypothesis that must be rejected. N e w methodologies (such as advances in D N A sequencing techniques and a new way of tracking the course of evolution called phylogenetic systematics (also k n o w n as cladism, it is described in more detail below) and recent discoveries of previously u n k n o w n living and fossil nautiloid specimens have drastically changed our understanding of these ancient animals. O u r current knowledge would have been paleontological heresy even a decade ago: T h e nautilus n o t only dates back to (and lived through) the great K / T calamity but also became the rootstock for an evolutionary radiation of new nautiloid genera in the ensuing Cenozoic Era. A n d (heresy of heresies!) our world is graced with not o n e but two genera of living nautiloid cephalopods. H o w we arrived at these new understandings is perhaps as fascinating as the animal itself, for the recent elucidation of the nautilus's great feat of survival—it has lasted at least 100, and perhaps 200, million years—is a saga of h o w science often works. It frequently progresses in fits and starts, is shaped the influence of forceful personalities and c h a n c e discoveries, and is hampered by many decades of mistaken identity. T h e pearly nautilus, w i t h its spiraled, chambered shell, is often grouped with the c o e l a c a n t h , t h e opossum, and the dragonfly as living fossils— archaic creatures t h a t h a v e s o m e h o w survived to t h e present. In Charles 174

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Darwin's time, the nautilus was certainly accepted as a living fossil. But duting the last century, our definition of w h a t is (and what isn't) a living fossil has changed: We now regard t h e m n o t only as organisms of great antiquity but also as belonging to evolutionary groups that, t h r o u g h time, h a v e produced very few species. T h i s is a subtle but i m p o r t a n t difference from the earlier definition. S o m e facets of a living fossil's habitat, ot habits, n o t only preserve it from e x t i n c t i o n but also s o m e h o w inhibit t h e process t h a t leads to new species formation. Nautilus was sttuck from t h e rolls of b o n a fide living fossils w h e n paleontologists realized t h a t in b o t h of these attributes it differed very m u c h from the o t h e r recognized living fossils. G e n e r a of nautiloid cephalopods ( t h e group to w h i c h nautilus belongs) typically c o n t a i n n u m e r ous species, not few; and most troubling of all, t h e genus Nautilus seemed n o t to be of great antiquity at all, but rather a recently evolved t a x o n .

A l i v i n g fossil? My scientific studies of t h e nautilus, whose earliest relatives are found in Camhrian-aged rocks only slightly younger t h a n those in t h e storied Burgess Shale of C a n a d a , dated back to 1975, w h e n 1 took time out from my work on Vancouver Island to spend t h r e e m o n t h s living on t h e tropical Western Pacific islands of N e w C a l e d o n i a and Fiji studying these odd creatures. My m o tive at t h a t time was simple: T h e life of t h e living nautilus provided t h e best time m a c h i n e with which to extract a m m o n i t e s from their a n c i e n t past. I wanted to bring the Vancouver Island C r e t a c e o u s back to life. A n d to do that, I needed to study the living as well as t h e dead. I had collected many nautilus fossils from Sucia Island and elsewhere. I was familiar with the living nautilus's shell, of course, hut like most people had never seen the animal t h a t lives inside, because nautiluses occupy deepwater habitats of the western Pacific O c e a n . I had supposed t h a t t h e living animals would be more snail-like t h a n a n y t h i n g else; their shells resemble n o t h i n g so m u c h as large snails of some peculiar ancestry. But during those three wonderful m o n t h s so long ago, I learned my mistake many times over as I observed t h e habits of living nautiluses in their natural h a b i t a t on the 175

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seaward edges of N e w C a l e d o n i a . W i t h members of a local French oceanographic institution, O R S T O M , I would dive t h e magnificent outer barrier reefs of this island after s u n d o w n , and I was routinely rewarded with sightings of these beautiful animals as they concluded their long nocturnal ascents from their d e e p daytime habitats. T h e N e w Caledonian barrier reefs parallel the Great Barrier Reef of Australia and, like the latter, form great vertical walls extending from the warm surface to cold, thousand-foot muddy bottoms. During the day, the nautiluses lurk on the deep bottoms, out of sight and danget from the efficient shell-breaking predators of the reefs' shallower regions. But at night, emboldened, they swim up the reef walls to the shallows, where they feed under cover of darkness. Like h o t air balloons, they would rise upward along the reef walls, and night after night I would wait for them, hanging weightless in hundred-foot depths, sweeping the black water with my dive light to catch a glimpse back into time. Sooner or later an isolated specimen would swim into view—they always travel alone—and I could follow it on moonlit nights into shallower water without lights. Nautiluses swim vigorously; they are nobody's placid snail. My initial work was entirely c o n c e r n e d with h o w a nautilus uses its c h a m b e r e d shell to achieve and t h e n m a i n t a i n neutral buoyancy in t h e sea. At the time I h a d no research interest in t h e evolutionary history of this animal, and for good reason: That story had long b e e n worked out to virtually every biologist's satisfaction. Just as no physicist would b o t h e r recalculating the speed of light, n o r any biologist again a t t e m p t to show t h a t D N A is the molecular basis of heredity, so too was working out t h e evolutionary history of t h e e x t i n c t a n d e x t a n t nautiloid cephalopods, at least as understood in the 1970s, viewed as a job already d o n e . Two giants of A m e r i c a n paleontology had said all t h e r e was to say on t h e phylogeny of the nautiloids—and of Nautilus—in t h e 1950s. Or so we all t h o u g h t . A l t h o u g h t h e n a m e Nautilus was applied to b o t h fossil and living taxa during t h e n i n e t e e n t h and early t w e n t i e t h centuries, by t h e 1950s the name was restricted to t h e living species, e v e n t h o u g h it was recognized t h a t many fossil forms were morphologically similar to t h e living species. T h i s change in c o n c e p t was brought about largely t h r o u g h the landmark work of A. K. 176

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Miller of t h e University of Iowa, t h e n t h e feigning expett on nautiloid cephalopods. Millet, a workaholic of amazing e n d u r a n c e and longevity, had the interesting habit of airbrushing t h e p h o t o s of his nautiloid specimens to make t h e m look bettet in his published m o n o g r a p h s . In spite of such idiosyncrasies (today considered a n a t h e m a in all scholatly publications), he was unchallenged in his specialty. He was a c h a m p i o n of distinguishing taxa on the basis of only o n e or two morphological characters. For instance, in his most i m p o t t a n t work, published in 1947, he wrote, In general, diffetences in suture p a t t e r n [a s t m c t u r e formed by t h e intetsection of the shell wall and the septum t h a t is visible only w h e n t h e shell wall is removed] and o r n a m e n t a t i o n must be given far mote weight t h a n shape of t h e c o n c h in t h e d e t e r m i n a t i o n of the t a x o n o m i c position of a genus or species of nautiloid cephalopods. . . . Miller's subsequent description of the genus Nautilus was indeed based largely on the morphology of the suture pattern. He also recognized only living species as members of genus Nautilus. T h e s e two c o n c e p t s — t h a t nautiloid genera (including Nautilus) were best differentiated by sutures and o r n a m e n t , and that the genus Nautilus had no fossil record—were subsequently adopted by Millet's heir to the title of world authority on the nautiloids, Bernard Kummel of Harvard University, who, like Miller, believed that Nautilus first evolved in the Late Tertiary (perhaps 5 million years ago) and was without any fossil record. In 1956 in a latge m o n o g r a p h dealing with every k n o w n nautiloid species from the Jurassic Period to the modern day, Kummel noted, " N o fossil species are assigned to the genus Nautilus. No Pliocene or Pleistocene nautiloids are known." T h i s view made Nautilus anything but a living fossil. Millet and Kummel also framed a standard species c o n c e p t for fossil nautiloids. T h e y believed t h a t nautiloid genera were highly prone to producing new species. By Miller's time, over a t h o u s a n d post-Triassic-aged nautiloid species had been recognized by paleontologists. Eithet there were an extraordinary n u m b e r of these cteatures swimming the world's oceans through time, or the species c o n c e p t for nautiloids was exceedingly narrow. 177

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U n t i l recently, t h e only assertion t h a t Nautilus might be more ancient t h a n Millet and K u m m e l believed came from a Russian n a m e d V. S h i m a n sky, w h o in 1957 published t h e description of a nautiloid fossil from rocks 30 to 40 million years old in Kazakhstan. He n a m e d this specimen Nautilus praepompilius n.sp. Because it was remarkably similar in shell morphology to Nautilus pompilius, Shimansky suggested t h a t t h e genus Nautilus might be traced back to t h e mid-Tertiary, rather t h a n to the later Tertiary or Pleist o c e n e . But Shimansky's n e w species was k n o w n only from a single specim e n , so it was largely ignored by subsequent workers. Miller and Kummel's claim t h a t Nautilus was very recently evolved, and therefore h a d no fossil record, was endorsed by each new generation of paleontologists interested in cephalopods, including J. W i e d m a n n in the 1960s, J. Dzik in t h e 1970s, and C. Teichert and T. M a t s u m o t o in t h e 1980s. T h e latter two had a century of c o m b i n e d experience studying nautiloids by t h e time, in 1987, w h e n they wrote an atticle on nautiloid systematics and evolution teaffirming t h a t Nautilus, t h o u g h perhaps somewhat older t h a n Miller and Kummel imagined, was the last-evolved externally shelled cephalopod, was recently evolved, and was t h e only such creature left in the world today. W h o could argue with this Who's Who a m o n g t h e greatest paleontologists of t h e t w e n t i e t h century?

A n e w s c h e m e of c l a s s i f i c a t i o n All taxonomists of this period (including, of course, those working on cephalopods) used a similar scheme of classification: Organisms were grouped together into taxa because they shared specific morphologies. O p i n i o n s on which characters were most i m p o r t a n t in this endeavot, however, were based on e a c h worker's experience and observations, so they differed greatly among scientists. " G o o d " systematic biologists were those w h o had a "feel" for defining i m p o r t a n t characters. T h i s m e t h o d , called phenetics, was originated and used by such pioneering e i g h t e e n t h - and n i n e t e e n t h - c e n t u r y taxonomists as Linnaeus, Cuviet, a n d O w e n , and it persisted t h r o u g h t h e first half of the t w e n t i e t h century. By t h e 1970s, however, a contrasting philosophy and 178

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methodology for discerning evolutionary lineages began to c o m p e t e with phenetics. T h i s new t e c h n i q u e was k n o w n as phylogenetic systematics, or, as it came to be called, cladism. T h e beauty of cladistics is that, w h e n correctly applied, it is far less subjective t h a n p h e n e t i c m e t h o d s . Instead of focusing on o n e i m p o r t a n t character, or at best on a few (what is " i m p o r t a n t " being d e t e r m i n e d by t h e practitioner), a cladist tries to use multiple characters, thus eliminating t h e need for deciding subjectively which characters, or traits, should be chosen. Furthermore, it is n o t t h e shated presence of specific characters t h a t is used to define taxa but rather t h e n u m b e r of shared "derived" c h a r a c t e r s — t h a t is, characters t h a t h a v e u n d e r g o n e evolutionary transformation from more primitive states. For example, all vertebrate animals (such as h u m a n s ) h a v e forelimbs of some sort. T h i s c h a r a c t e r has b e e n "derived" into wings in birds. Because all birds share this derived character (as well as sharing a greater n u m b e r of o t h e r derived characters t h a n they h a v e in c o m m o n with any other group of animals), they are grouped together into what we call a clade. T h u s , whereas b o t h pheneticists and cladists search for and "use" characters, a cladist gives each character at least two states: primitive and derived. At last, a new and objective philosophy of classification could be employed. Its availability d e m a n d e d t h a t every group, every past classification, be reexamined. Nautiloid cephalopods, past and present, were no exception. As the cladistic revolution was sweeping t h r o u g h paleontology and systematic biology in t h e early 1980s, I was m o v i n g westward across t h e Pacific O c e a n , island group by island group, still primarily studying buoyancy in t h e Nautilus. But the great c h a n g e in h o w we classified organisms brought about a shift in my interests from functional morphology to evolution, and as I saw more and more nautilus specimens, and thus was able to observe variability both within and between isolated nautilus populations, I began to doubt t h e then-accepted phenetics-based classifications of t h e living and e x t i n c t nautiloids. Most extinct nautiloid species were k n o w n from only a handful of representatives—or e v e n from a single specimen. C h a r a c t e r variability within a given species was t h o u g h t to be very low, but because so few specimens were typically k n o w n , this interpretation was still unsubstantiated. 179

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Nevertheless, c e p h a l o p o d paleontologists such as Miller and Kummel had used e v e n t h e slightest morphological difference in suture, shell shape, or orn a m e n t as an excuse to declate n e w species. A d d i n g to this was the fact that status a m o n g paleontologists was often accorded to those w h o "discoveted" t h e most new species d u t i n g a career. T h e r e was thus incentive (promotion, pay, prestige) to a n n o u n c e the discovery of as many new species as possible. N o t surprisingly, "new" species proliferated in t h e literatute. By t h e early 1980s I was n o t alone in harboring a deep suspicion of currently accepted nautiloid taxonomy, for by this time a n o t h e t paleontologist intetested in cephalopods, Dt. Bruce Saunders of Bryn Mawr College, had also spent several years studying living nautilus populations. He too had doubts about t h e classification of Nautilus. In 1983 we joined forces to try to understand these creatures' evolutionary history. O u r first task was to discover exactly h o w m a n y species of t h e genus Nautilus exist today.

Classifying the nautilus T h e n u m b e r of living Nautilus species has long b e e n in dispute. By the mid1800s, four species were c o m m o n l y recognized: t h e widespread Nautilus pompilius,

N.

macromphalus from N e w C a l e d o n i a , N.

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G r e a t Barrier Reef of Australia, and N e w Guinea's N. scrobiculatus, also k n o w n as t h e King Nautilus. Remarkably little was k n o w n about these fout species, because only two (N. pompilius and N. macromphalus) had ever been seen alive. T h e o t h e r two accepted species, N. stenomprialus and N. scrobiculatus, had (like all fossil nautiloids) b e e n defined on shell characters alone; they were k n o w n only from drift shells without soft parts. By this century, many more nautilus shells had b e e n collected from isolated island groups across t h e Pacific O c e a n , and, given t h e philosophy of classification t h e n d o m i n a n t , it is n o t surprising t h a t m a n y more new species were defined, including N. repertus, N. alumnus, N. perforatus, N. ambiguous, and, most recently, N. belauensis. Yet all save t h e last were k n o w n only from shells, and t h e i t supposed differentiation as distinct species was based only on perceived differences in shell shape or size. It seemed to many c e p h a l o p o d specialists 180

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that a tremendous diversity of living Nautilus species existed. But o n e nagging problem remained: In t h e three species from w h i c h soft parts as well as hard parts were k n o w n , the soft parts were absolutely identical in anatomy. A n d on the basis of t h e great variability in mature shell size, shell o r n a m e n t , and shell geometry a m o n g t h e various "species" observed by Saunders and myself, it seemed doubtful t h a t all of these denned nautilus species could be valid. Clearly, we needed more information n o t just from t h e hard parts, but from all anatomical characters, of t h e living Nautilus species. It was thus imperative to capture living s p e c i m e n s — a n d especially those forms from w h i c h no soft-part a n a t o m y was yet k n o w n . Of all of t h e "species" d e n n e d only by shells, we were most interested in observing a living "King Nautilus," N. scrobiculatus. U n l i k e t h e o t h e r Nautilus "species," w h i c h differ only slightly in shell shape, this latter has a shell radically different from any o t h e r nautilus. For instance, its coiling configuration is such t h a t it has a very large, central depression in t h e shell ( t h e umbilicus). It also exhibits a square (rather t h a n rounded) cross section and a peculiar, cross-hatch shell sculpture unique a m o n g living nautiloids. Yet in spite of h u n d r e d s of its shells having been found, no living s p e c i m e n — a n d thus no example of its soft parts—was k n o w n . O n l y a single tantalizing clue existed: At t h e turn of the last century, an English zoologist n a m e d A r t h u r Willey had found a rotting carcass within the shell of a beach-stranded N. scrobiculatus on a r e m o t e N e w G u i n e a beach. T h e soft parts appeared quite distinct from those typical of any of the o t h e r living Nautilus "species." But t h e advanced state of decomposition precluded obtaining any definitive answer. It would be more t h a n 80 years (and several generations of c e p h a l o p o d specialists later) before this most enigmatic of living nautiloids was finally seen alive. T h e finding of t h e c o e l a c a n t h , t h o u g h t to h a v e b e e n e x t i n c t for over 100 million years at t h e time of its capture, surely ranks as t h e foremost discovery of a living fossil in this century, and t h e recovery soon thereafter of a small mollusk named Neopilina (considered to h a v e been e x t i n c t since the Paleozoic Eta) was exciting as well. But a third discovery, the first capture of a living Nautilus scrobiculatus by Bruce Saunders, must be reckoned with 181

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these others for many reasons. T h e o t h e r two discoveries occurred by sheer c h a n c e ; Saunders's discovery was a t r i u m p h of ingenuity and intellectual sleuthing. Saunders at least h a d t h e benefit of k n o w i n g t h a t his animal existed. But his rapid discovery first of its h a b i t a t site and t h e n of the living animal itself, was extraordinary. A r t h u r Willey searched for this animal for two years and never found it. W i t h i n a week of arriving in N e w G u i n e a in 1983, Saunders h a d captured this prized creature. A n d what a creature it was. T h e shelled c e p h a l o p o d t h a t Saunders captured in the deep blue sea off M a n u s Island, had a completely u n e x p e c t e d appearance, for it looked almost n o t h i n g like t h e nautiluses we had grown so familiar with. A n d it was not alone, for Saunders began c a t c h i n g b o t h Nautilus pompilius and the "King Nautilus" at t h e same locality. Saunders discovered n o t only t h a t two completely different types of nautiloids lived on e a r t h but also t h a t they lived side by side in t h e same habitat. I was able to see these extraordinary creatures in J u n e of 1984 w h e n I traveled to N e w G u i n e a with Bruce Saunders. W e r e able to c a t c h more of these odd nautiloids. T h e i r shells were quadrate, with weak yellow stripes, and t h e soft parts looked quite unlike those of a nautilus, for the upper body was covered with thick, fleshy tubercles t h a t are lacking in all o t h e r Nautilus species. But t h e most striking feature was t h e shell's cover. A thick, shaggy, orange fur covered t h e shell, almost completely obscuring the shell ornam e n t and m a k i n g t h e creature look like it wore a fur coat. T h u s was my first view of Nautilus scrobiculatus, also k n o w n as t h e King Nautilus. O v e r time we trapped more of t h e m and t h e n released t h e m back into t h e sea to swim with t h e m . T h e y looked and behaved unlike any of the other Nautilus species we were familiar with. T h e i r shells also bore an u n c a n n y resemblance to o n e of t h e most a n c i e n t (and t h e most c o m m o n ) of Mesozoic nautiloids, a genus n a m e d Cenoceras. A heretical t h o u g h t crept in to our discussions: C o u l d this living animal, for almost two centuries placed in the genus Nautilus, actually belong to a new genus? Or (an e v e n more exciting prospect), could it be an undiscovered living fossil that had existed on earth, without leaving any fossil trace, since t h e Jurassic Period? T h i s question 182

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could be answered only by looking in more detail b o t h at t h e fossils and at modern nautiloids. In late 1994, Saunders and I finally got a r o u n d to looking at t h e softpart a n a t o m y of Nautilus scrobiculatus. We performed a series of parallel dissections on the soft parts of t h e King Nautilus and Nautilus pompilius. T h e t i m e - h o n o r e d m e t h o d of comparative a n a t o m y is o n e of t h e most powerful m e t h o d s applied in elucidating evolutionary relationships and thus is a "time m a c h i n e " in its own tight. O u r work showed t h a t Nautilus scrobiculatus, t h e so-called King Nautilus, was distinct in many a n a t o m i c a l characters, such as gill and reproductive system morphology, shell ultrastructure, and morphology of the h o o d . T h u s in soft-part as well as hard-part a n a t o m ical featutes, it was clearly distinct. But was it ancestral, or was it a descendant of some Nautilus species, or was it completely unrelated? To addtess such evolutionary issues, we needed to perform a cladistic analysis, and to do that, we needed to know which characters were primitive and w h i c h derived. Unfortunately, we still did n o t h a v e e n o u g h information to make such judgments. H e n c e we turned to a n e w source of evolutionary evidence: t h e genes of the nautiloids themselves. By the 1980s, extremely powerful t e c h n i q u e s based on D N A sequencing afforded investigators new ways of testing phylogenetic hypotheses such as those we had framed for the living nautiloids. T h e power of t h e D N A methodology is t h a t , unlike the traditional nautiloid t a x o n o m y pioneered by Miller and Kummel, it looks at many individual characters ( t h e genetic arrangements) rather t h a n only a few ( t h e shell and sutute characters) and thus allows t h e use of the new cladistic approach. But for these tests, tissues from live animals h a d to be obtained, frozen immediately at very low temperatures, and kept frozen until t h e laboratory analyses were obtained. T h i s posed huge problems for those of us collecting samples from living nautiloids. T h e s e animals lived in r e m o t e , tropical localities. In many such places there was no possibility of o b t a i n i n g dry ice, t h e substance used to fteeze and t h e n m a i n t a i n t h e tissues. T h e logistics of freezing t h e samples and t h e n getting t h e m back to N o r t h A m e r i c a from distant tropical regions was daunting. It took us 5 yeats. 183

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Tissue samples were ultimately o b t a i n e d from 13 geographically distinct nautiloid populations a m o n g t h e "species" Nautilus pompilius,

N.

macromphalus, N. stenomp/ia!us, N. belauensis, and N. scrobiculatus from numerous localities in Fiji, Samoa, Australia, N e w G u i n e a , t h e Philippines, Palau, and N e w C a l e d o n i a . T h e s e tissue samples were analyzed first in the lab of David Woodruff of t h e University of California at S a n Diego, using a t e c h n i q u e called gel electrophoretics, and later, using more powerful D N A sequencing techniques, by geneticist C h a r l e s Wray at the A m e r i c a n Museum of N a t u r a l History. Both sets of analyses yielded t h e same surprising result: O n l y two distinct groups emerged. O n e group was composed of Nautilus scrobiculatus, w h i c h (according to t h e molecular "clock" approach of analyzing genetic distance, w h i c h compares differences in D N A results to an estim a t e d rate of c h a n g e in all D N A molecules) appears to h a v e descended from an u n k n o w n Nautilus species s o m e t i m e in t h e M i o c e n e Epoch, or about 15 million years ago. T h e other group was composed of all other Nautilus "species." "Nautilus" scrobiculatus is so different in its gene sequences from Nautilus that David Woodruff suggested to me t h a t it might n o t e v e n belong in the same family as Nautilus, let alone t h e same genus. T h e results suggested t h a t n o t only did t h e many isolated populations of N. pompilius all fall into t h e same species ( w h i c h was at least comforting) but so too did N. belauensis, N. stenomphalus, and (to a slightly lesser e x t e n t ) N. macromphalus. T h e genetic results suggested t h a t separating out these latter as distinct species of Nautilus made little biological sense, and indeed Saunders and I provided i n d e p e n d e n t confirmation of this with our discovery t h a t Nautilus stenomphalus, w h i c h we captured for t h e first time alive in 1986, was apparently breeding with N. pompilius on t h e G r e a t Barrier Reef of Australia. If t h e genetic evidence was to be believed, t h e n t h e long-accepted classification of t h e living species assigned to Nautilus had crumbled. N o t only did N. scrobiculatus appear to represent a different genus, but the slight differences in shell morphology of t h e o t h e r species classically placed in Nautilus appeared to be of little or no t a x o n o m i c significance. We had gone from five species belonging to o n e genus, to two genera, e a c h with o n e species. In184

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stead of being composed of many species, Nautilus was beginning to look much mote like a typical, low-diversity living fossil. In 1995 we n a m e d t h e other living nautiloid genus Allonautilus (alio means " o t h e r " ) . T h a t was all very well, but now we were in a quandary. It appeated t h a t shell characters and genetic chatacters were giving two very different classifications for t h e Nautilus species. A n d because t h e shell chatacters used originally to define t h e living Nautilus species by t h e classical taxonomists Linnaeus, Sowetby, and Lightfoot in t h e e i g h t e e n t h and n i n e t e e n t h centuries were t h e same ones used by Millet and K u m m e l in t h e t w e n t i e t h century fot classifying fossil nautiloid species and geneta, it appeated t h a t if t h e m o d e r n day species were oversplit (too narrowly defined), so too might be t h e t h o u sands of fossil nautiloid species. But could t h e genetic results be trusted? Didn't the c o m b i n e d paleontological wisdom of so m a n y past students of the fossil cephalopods m e a n more t h a n a few genes? To answer these questions, we had to e x a m i n e the fossil record, as well as genes and living animals, using cladistics.

Cladistics to the rescue Bruce Saunders and I thus embarked on a new a t t e m p t to reconsttuct the phylogeny of all nautiloid geneta since t h e Jurassic Period. O u r intetest was stimulated equally by our a n a t o m i c a l research on Nautilus scrobiculatus and by the newly emerging D N A work c o n d u c t e d on tissues t h a t t h e two of us had obtained in the 1980s. But a third source of evidence also was emerging, for many new discoveries of fossil nautiloids became available in t h e early 1990s as well. We intended to use cladistics to analyze t h e various genera and species of nautiluses b o t h living and dead. O u r nearly two decades of studying N a u tilus species had given us new insight into just what a fossil "species" ought to encompass in tetms of variability; we thus used t h e m o d e r n animals as a guide to interpreting fossil taxa. But we needed more t h a n simply an understanding of variability to conduct such a study: We needed many additional hard-part 185

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characters t h a t could he recognized in fossils. T h e traditional shell characters, such as shape, o r n a m e n t , and sutute type, were useful but too few in n u m b e r to allow meaningful cladistic analysis. Luckily, just at this time a wealth of morphological characters, buried deep in t h e middle of every nautiloid, was discovered t h r o u g h t h e detailed work of Neil L a n d m a n of the A m e r i c a n M u s e u m of N a t u r a l History. T h e nautilus has long b e e n k n o w n to h a t c h at a very large size: It emetges from its egg with seven fully formed chambers and a shell diameter of over an inch, w h i c h makes it t h e largest invertebrate, at h a t c h i n g , in the world. Indeed, it may h a v e b e e n this trait t h a t enabled it to survive the gteat Cretaceous mass e x t i n c t i o n , for t h e nautilus appears to lay these eggs in very deep watet w h e t e they take a year to h a t c h , and it may h a v e been the deepliving juveniles, or e v e n t h e u n h a t c h e d eggs, t h a t survived in this refuge. W h e n a young nautilus emetges from its egg, a distinct mark is left on its shell. L a n d m a n began dissecting many types of fossil nautiloids to see whether similar marks were found in a n c i e n t species as well. He discovered n o t only t h a t these marks did occur but also t h a t many other types of characters could be found in t h e h a t c h i n g stages of all nautiloid fossils. By c o m b i n i n g these traits—shell shape complexity of sutures, ornam e n t a t i o n , and h a t c h i n g s t a g e — S a u n d e t s and I finally had e n o u g h characters to perform a meaningful cladistic analysis of fossil nautiloids. To our surprise, these analyses showed t h e genus Nautilus to be extremely primitive. R a t h e r t h a n being a d e s c e n d a n t of some Late Tertiary (perhaps 30-millionyear-old) nautiloid genus such as Eutrephoceras or Hercoglossa, Nautilus appears to be derived from a m u c h older ancestor, probably t h e Jurassic-aged, 180-million-year-old Cenoceras t h a t our new genus Allonautilus so resembles. Furthermore, rather t h a n being t h e last-evolved nautiloid genus, it seems to h a v e b e e n a m o n g the first of its family and t h e ancestor of most of the C e n o zoic Era nautiluses. T h e r e was only o n e problem: If Nautilus was so old, why were t h e r e no fossils of it? It turns out t h a t t h e r e are many fossils t h a t we c a n n o w confidently place in t h e genus Nautilus. T h e first to point this out was t h e paleontologist Richard Squires of California. Squires, a specialist in Tertiary-aged mollusks, 186

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was given a collection of nautiloid fossils from W a s h i n g t o n state to analyze. These specimens belonged to a fossil species assigned to t h e genus Eutrephoceras by A. K. Miller in his famous 1947 treatise. Squires, however, was the first to declare t h a t this particular emperor had no clothes. He had t h e intellectual courage to challenge Miller and t h e others by assigning his fossils to the genus Nautilus. Squires thus confirmed t h e 1957 discovery by t h e Russian Shimansky, as well as e x t e n d i n g the k n o w n range of Nautilus back at least 40 million years. Nautilus now had a fossil record. But n o t e n o u g h of a one yet to jibe with the implications of our cladistic studies. At about the same time t h a t Squires's heresy was provoking t h e ghosts of A. K. Miller and Bernard Kummel to roll over in their graves, sheer c h a n c e played a part in this story. In 1988 I had t h e privilege of e n t e r t a i n i n g Steve Gould of Harvard University at my house for lunch prior to o n e of his speaking engagements. It was a perfect day, we had plenty of time, and because I had on my m a n t l e a fossil nautiloid collected from Cretaceous deposits in California t h e year before, our conversation eventually turned to this particular specimen. So there it sat in my house, just waiting for Steve Gould to get invited to lunch. Steve looked at this large, beautifully preserved nautiloid fossil, and p r o n o u n c e d , "Looks like Nautilus to m e . " At t h e time I was aghast: Didn't t h e learned Steve G o u l d k n o w t h e r e were no C r e taceous Nautilus? After all, he h a d worked alongside Bernie Kummel at Harvard for years and he was surely aware t h a t t h e r e were n o t e v e n any fossil Nautilus, let alone Cretaceous-aged specimens. But t h e c o m m e n t stayed with me, and later, after Squires's paper about Tertiary-aged Nautilus from the west coast of N o r t h A m e r i c a was published, I began to wonder w h e t h e r Gould and Squires were right. M i g h t these west coast specimens be t h e missing fossil nautiloids t h a t our cladisitic analyses suggested should be present? T h e r e was only o n e way to test this: C u t t h e m o p e n and e x a m i n e their h a t c h i n g stage, which would give us more characters with w h i c h to test their pedigree. T h e Tertiary-aged species described by Squires and t h e Cretaceousaged specimens from California, w h e n cut, showed h a t c h i n g stages identical to those of the m o d e r n nautilus. Like t h e m o d e r n nautilus, they h a t c h e d at 187

Evolutionary history of Nautilus and AUonautilus.

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over an inch in diameter, with seven fully formed septa. S o o n we found other nautiloid specimens squirreled away in various museum collections. C u t in half, they also showed internal shell characters t h a t , w h e n added to other shell and suture character states, gave telltale e v i d e n c e of b e i n g — o r in some cases not b e i n g — m e m b e r s of t h e genus Nautilus. We had s h o w n t h a t Nautilus lived in Cretaceous seas, and more recently we h a v e found Jurassic specimens that indicate that this wondrous creature may h a v e lived as along as 200 million years ago. A final o u t c o m e of all of this is t h e need to suppress h u n d r e d s of species defined for various nautiloid genera. To date we c a n confirm only three (and perhaps four) discrete species of Nautilus: t h e modern-day N. pompilius, perhaps the modern day N. macromphalus ( w h i c h may turn out to be a subspecies of N. pompilius), and a ribbed species from t h e C r e t a c e o u s of Vancouver Island. T h e others, including t h e hundred-million-year-old specimen that Steve Gould resurrected from my m a n t l e ( n o w sitting safely, if less eloquently, in a dark museum drawer) may all simply be Nautilus pompilius. On the basis of shell characters, t h a t is certainly what they seem to be. T h i s raises a profound evolutionary question. C a n any "species" exist for such a long period of time? A l t h o u g h t h e t e are many k n o w n cases of genera lasting for a h u n d r e d million years, the persistence of a species for so long is far more problematical, especially t h a t of a species of a creature as complex as a cephalopod. W o u l d n ' t genetic drift—the rather r a n d o m evolutionary change that can affect any p o p u l a t i o n — e v e n t u a l l y result in a new species over such immense periods of time? Or would our hundred-million-year-old nautilus, if somehow brought back to life, happily and successfully m a t e with a Nautilus pompilius from today's oceans? Is a hundred-million-year-old species n o t a rare exception, but perhaps more c o m m o n t h a t we think? A r e there even billion-year-old species on e a r t h , perhaps a m o n g t h e bacteria, blue-green algas, or e v e n flatworms, annelids, and mollusks as well?

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To t h e n o r t h of Sucia Island lie t h e C a n a d i a n Gulf Islands, an isolated archipelago made up of the same C r e t a c e o u s strata we find on t h e U . S . side of the international b o u n d a r y — t h e mixture of shale, sandstone, and conglomerate so typical of t h e N a n a i m o G r o u p formations. T h e C a n a d i a n Gulf Islands float like serene battleships off the coast, but getting to t h e m is e v e n harder t h a n making port at Sucia. Unless you cheat (like t h e many smugglers in the region) and scoot across in a fast boat, t h e Gulf Islands are a long travel day from the U n i t e d States. You h a v e to take a British C o l u m b i a ferry out of t h e crowded Vancouver tetminals, but o n c e you are loaded aboard, conditions improve considerably; t h e sea voyage is spectacular as you head

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west, crossing t h e wide Strait of Georgia with the m o u n t a i n o u s Vancouver Island looming in t h e distance. O n c e you arrive on these eagle-infested C a n a d i a n islands, it is clear t h a t you are out of t h e U n i t e d States: better beer, worse food, no Starbucks coffee (but mercifully no M c D o n a l d s either), and everywhere t h e lilt of C a n a d i a n English with t h e distinctive "ehs" creatively interspersed in every s e n t e n c e . T h e s e islands are long and t h i n , carved by t h e glaciers with a n o r t h - s o u t h whim, and they form a rampart t h a t seems to protect V a n c o u v e r Island from an e n c r o a c h i n g N o r t h America. O n e of the longest of these islands is Gabriola Island. Its few, rare a m m o n i t e fossils tell us t h a t its strata are n o t so old as t h e rocks of Sucia. Gabriola contains some of the youngest, and thus last-formed, rocks still of Mesozoic age in all of western C a n a d a . S o m e w h e r e buried in its youngest rocks is a C r e t a c e o u s / Tertiary boundary site, t h e boundary b e t w e e n t h e Mesozoic and Cenozoic Eras n o w t h o u g h t to h a v e b e e n formed by t h e impact of a giant c o m e t 65 million years ago.

A n a n c i e n t giant c l a m T h e rocky n o r t h e r n coast of this island is largely u n i n h a b i t e d , although a road still gives access to it. O n e can easily find a trail through the salal and huckleberries, scrambling past t h e red-barked arbutus trees and o n t o a beach replete with strata. Black shale greats us, a shale dense with fossils and living oysters, and sometimes it is hard to tell t h e dead from t h e living. T h e fossils d o n ' t j u m p out at you, but they seem ubiquitous o n c e you learn to spot them. T h e problem is t h a t these fossils are almost unrecognizable as the remains of a n c i e n t life. T h e y are large, usually t h e size of a d i n n e r plate but sometimes as large as 3 feet across, yet so t h i n t h a t they often appear as only slender white lines in t h e middle of sttatal blocks. W h e n we find a particularly large specimen t h a t has been eroded into view, we can see t h a t it looks like a gigantic oyster with a t h i n shell, t h e shell material covered with numerous fine ribs and some coarser undulations. Well-preserved specimens can be identified as some kind of giant clam. But h o w peculiar! T h e r e are no 3 -foot clams on e a r t h today with shells only 1/8 inch thick. T h e s e odd clams with nearly 192

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paper-thin shells are scattered in e n o r m o u s profusion: t h e giant inoceramids, extinct for 65 million years. C l a m s they are and huge as well, hut they are n o t "giant clams" in the sense of the familiar giant clams, or Tridacna, so a b u n d a n t in t h e tropics today. Tridacnas are large, thick-shelled creatures living a m o n g t h e coral reefs. T h e giant clams of these C a n a d i a n beaches are n o t e v e n closely telated to the living tridacnas. Instead, they were a kind of giant o y s t e r — t h i n k of the chowder that could be made from such b e h e m o t h s ! T h e Gabriola Island beach we visit is absolutely packed with t h e things. Gabriola Island is n o t u n i q u e in possessing a large n u m b e r of gigantic clams of Cretaceous age. Sucia has m a n y inoceramid clams ( t h o u g h n o n e so large as those on G a b r i o l a ) . In fact, most m a r i n e rock of U p p e r Cretaceous age anywhere in the world harbors inoceramid clams in varying, sometimes fantastic numbers. T h e s e clams may h a v e b e e n t h e most a b u n d a n t type of larger life on earth in t h e C r e t a c e o u s Period. S u c h mass occurrences are found elsewhere in t h e V a n c o u v e r Island region, such as on H o r n b y Island, G a l i a n o Island, and some of t h e rivers far up the Strait of Georgia. T h e y also occur in Texas, on a beautiful beach exposure in San Diego, and at m a n y localities along t h e coast of Spain. It is always a spectacular sight: u n c o u n t e d giant clam shells littering t h e a n c i e n t sediment. Sometimes these shells are themselves covered with smaller shells, the remains of encrusting clams and worms and o t h e r small creatures t h a t used these islands of shell material as living quarters on t h e otherwise muddy bottoms. N o t h i n g on t h e b o t t o m of our world's oceans is e v e n remotely comparable. T h e central question is how these huge clams lived. Most, you see, are found in sedimentary deposits t h a t appear to h a v e accumulated in very deep water. In t h e oceans of today, there are very few clams of any sort in deep water, and certainly no clams up to 3 feet across. H e r e , t h e n , is a mystery. T h e Cretaceous Period was a time w h e n multitudes of giant clams lived in ateas of t h e ocean where no self-respecting clam lives today. W h a t sorts of creatures were these inoceramid clams? A n d perhaps more important, what kind of ocean did they live in? 193

An ancient giant clam the size of a plate. Cretaceous-aged inoceramid fossil, the most common type of bivalve shell from the Mesozoic Era, but now extinct.

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We will need at least two types of time m a c h i n e s to answer these two questions. T h e first is called trophic group analysis, and it is a discipline of ecology—or paleoecology if we are analyzing a n c i e n t life. T h e second is a m e t h o d that enables us to d e t e r m i n e t h e temperatures of t h e a n c i e n t sea by analyzing fossil shells for their oxygen isotopic ratios.

The concept of community We use trophic group analysis to e x a m i n e h o w energy flows t h r o u g h ecosystems. All life on the planet depends on energy, be it from t h e sun, from chemicals such as m e t h a n e , or from o t h e r organisms t h a t are s o m e h o w ingested. Organisms eat o n e another, and as they do so, they pass energy from one body to another. You could say t h a t t h e living associate along pathways of energy flow; such associations are often called c o m m u n i t i e s . C o m m u n i t i e s are generally defined as t h e recurrent associations of organisms through which energy flows. T h i s flow of energy is quite often referred to as a food c h a i n or a food web. Food chains and food webs are t h e m selves broken down into groups called trophic levels, or feeding types. T h e lowest level of a community's "trophic structure" is composed of those organisms that use inorganic energy sources (such as sunshine or m e t h a n e gas) to power the synthesis of inorganic c o m p o u n d s into living material t h r o u g h some chemical pathway. For example, plants carry on photosynthesis, transforming light energy and raw material into living material. S o m e types of bacteria use m e t h a n e gas as an energy source. All such organisms are called autotrophs. A u t o t r o p h s make up t h e base of t h e trophic structure in any c o m m u nity. T h e y themselves are t h e n c o n s u m e d by plant (or bacterial) grazers, the herbivores. T h e energy stored in t h e living material of t h e autotroph's bodies is t h e n transferred into new types of cells, those t h a t make up t h e bodies of the herbivores. In turn, the herbivores are e a t e n by carnivores, and the smaller carnivores by e v e n bigger carnivores; all, m e a n w h i l e , are being e a t e n by parasites. In this way energy flows t h r o u g h o u t the system, and the organisms in this system are all considered members of t h e same community. 195

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As we know, t h e r e are unequal numbers of organisms on earth, and these differences are often related to position in a food c h a i n or food weh. T h e most n u m e r o u s , or voluminous (it is more practical to measure the total volume of a group of organisms t h a n their individual numbers), are those organisms t h a t capture and incorporate t h e primary energy source; they may be plants or bacteria. T h i s volume is often teferred to as biomass, and in most c o m m u n i t i e s the biomass of plants is t h e largest in t h e system. Because the transfer of energy from plants to those animals t h a t eat plants is never complete (most energy is lost), t h e biomass of herbivores is normally only a fraction of t h e a u t o t r o p h biomass. In many ecological systems, herbivores acc o u n t for only about 1 0 % as m u c h biomass as t h e autotroph. T h e same ratio obtains for t h e carnivores t h a t eat t h e herbivores; they add up to perhaps 10% as m u c h biomass as t h e herbivores. If we arrange these biomass measures in tabular form, we quickly see t h a t t h e trophic groups make up a pyramid. T h i s trophic pyramid explains why large carnivores are so rare compared to herbivores and why plants are so a b u n d a n t compared with any of t h e animals t h a t eat t h e m . T h e s e and o t h e r simple principles are the rules t h a t enable ecologists to organize their u n d e r s t a n d i n g of living organisms. T h e y h a v e been applied (with less success) to t h e a n c i e n t world as well, in t h e discipline of paleoecology. T h e m a i n problem, as noted earlier, is t h a t we can see only the animals t h a t h a v e left fossils, and thus we h a v e a very biased view of the ancient world and its ecosystems. T h e s e simple rules are t h e guiding principles of paleoecology. Just as particular mixtures of animals and plants in our world define living associations, or c o m m u n i t i e s , so too should fossils found in recurring associations be considered a n c i e n t c o m m u n i t i e s . T h e relative a b u n d a n c e of the fossils should similarly be clues to a n c i e n t trophic structure. A n d most important, the types of organisms should be clues to a n c i e n t e n v i r o n m e n t s if we accept t h e principle of uniformitarianism, w h i c h states t h a t t h e present is a clue to t h e past. In our world, coral reefs are found in tropical latitudes in warm, clear, shallow seas. C o r a l reefs of t h e deep past may h a v e occupied deep, cold watet, but this is very unlikely, and m u c h information suggests t h a t reefs of 196

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the past inhabited e n v i r o n m e n t s very like those surrounding t h e reefs of today. In accordance with t h e principle of uniformitarianism, we use the lives of present reef animals to infer t h e biology of those n o w extinct. T h e types of organisms found in any community, be it m o d e r n or ancient, are adapted to their specific e n v i r o n m e n t s . As e n v i r o n m e n t a l conditions change, so do t h e animals a n d plants t h a t make up the various communities. All that said, what can we make of t h e inoceramid associations? W h e r e in the food c h a i n do they rest? W h a t did they eat, and w h o ate them? W h e r e do we find living analogs?

The mystery of the inoceramids T h e a n c i e n t ecosystem of Sucia Island is fairly recognizable. Most of its fossils are made up of clams and snails t h a t belonged to groups (if n o t to species) still living today. Most of the clams are forms t h a t lived in the sediment, much like t h e vast majority of today's clams. T h e s e types of clams, w h i c h are called infaunal suspension feeders, burrow to escape predators. T h e y feed by sucking large volumes of water t h r o u g h their necks and t h e n straining planktonic organisms from this ingested water. Because most of t h e p l a n k t o n is composed of single-celled plants, these types of clams are t h e herbivores of this ecosystem, t h e lowest rung of t h e food c h a i n above t h e autotrophs, which in this case are the p l a n k t o n . On Sucia, t h e clams are thus t h e lowest animal members of the trophic pyramid. Most of t h e snails from Sucia, on the other hand, were carnivores, and judging from t h e small bore-holes left in many of the a n c i e n t bivalves' shells, m a n y of t h e snails fed on bivalves. All in all, this assemblage of creatures on Sucia seems to make very good ecological sense. T h e r e are about ten times as many herbivorous forms (the clams and a few of t h e snails) as t h e r e are carnivores. T h e r e are a few oddballs—the inoceramids, for i n s t a n c e — t h a t sat on t h e s e d i m e n t rather t h a n living in it. Yet these small forms (usually just a few inches long) are so much like oysters that they do n o t seem incongruous. On Gabriola Island, however, and at so m a n y o t h e r localities around the world with an a b u n d a n c e of large inoceramid clams, things are far more 197

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strange. T h e food chains as represented in the fossil record are not chains at all, for on Gabriola the giant clams are the only fossils. T h e r e were surely many softpart organisms that left no fossil record, for there are many other signs of life, such as abundant trackways and trails, but other t h a n the very rare ammonite fossils, it is a land of inoceramids. W h a t is the nature of the trophic pyramid here? Perhaps the inoceramids fed on plankton and thus were the equivalent of the shallow-water clams. But there is a big problem with this scenario: T h e inoceramids appear to have lived at such great depths that they would have starved to death. T h e r e is no plankton pasture at the bottom of the sea. A great deal of paleontological research has addressed this question, and t h e answer c a m e from quite u n e x p e c t e d sources. T h e clues that helped us solve t h e mystery of t h e inoceramids came from two separate discoveries, o n e an act of genius, t h e o t h e r brought about completely by c h a n c e .

T a k i n g t h e t e m p e r a t u r e of a n c i e n t seas T h e act of genius occurred in C h i c a g o in t h e early 1950s and was t h e creative work of a N o b e l laureate from t h e University of Chicago, t h e chemist Harold Urey. Urey's discovery derived from the study of isotopes. An isotope is o n e of two or more atoms of a single e l e m e n t whose nuclei h a v e t h e same n u m b e r of protons but different n u m b e r s of n e u t r o n s . In an earlier chapter we saw h o w i m p o r t a n t t h e b r e a k d o w n of radioactive isotopes is in geological age d e t e r m i n a t i o n . O t h e r isotopes h a v e proved equally useful in a variety of geological investigations dealing with a n c i e n t e n v i r o n m e n t s . O n e of the most useful tools is oxygen isotopic ratios. Urey discovered that by measuring (with a mass spectrograph) t h e ratio of t h e very rare isotope oxygen-18 to t h e far more c o m m o n oxygen-16 from calcareous shells, he could deduce the temperature at w h i c h t h e shell formed. T h e warmer the temperature of shell formation, t h e less oxygen-18 there was in the shells. As long as the shell has n o t b e e n altered, t h e same types of analysis c a n be performed on fossil shells. Urey h a d devised a way to measure t h e temperatures of t h e ancient sea. 198

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In the decades following this m o n u m e n t a l discovery, thousands of scientific papers appeared detailing t h e tesults of oxygen isotope analyses of ancient temperature. S o o n a rough, and t h e n an increasingly more precise, picture emerged of global sea t e m p e r a t u r e t h r o u g h time. T h e most neatly continuous record of variation in m a r i n e t e m p e r a t u r e over the past 100 million years has c o m e from isotopic analyses of well-preserved foraminiferans (single-celled protist shells) recovered from d e e p sea cores. T h e r e were many caveats, of course. It did no good to compare t h e average b o t t o m temperature (as measured from shells of bottom-dwelling creatures) and t h e average t e m p e r a t u r e of surface water (as measuted from shells of p l a n k t o n i c creatures, w h i c h live mainly at t h e sea's surface), because b o t t o m water is always m u c h colder t h a n t h a t at t h e surface. But w h e n similar sorts of c o m p a r a t i v e analyses were m a d e , a q u i t e detailed picture emerged. T h e result of this work was to show t h a t t h e temperature of t h e sea has clearly fluctuated. T h e two warmest periods of t h e last 100 million years were during the Late Cretaceous (about t h e t i m e w h e n the rocks t h a t n o w m a k e up Sucia were deposited) and during t h e 50-million-year-old Eocene Epoch. T h e world's oceans appear to h a v e b e e n appreciably warmer during these two times t h a n they are now, e v e n in high-latitude seas. Many measurements of a variety of mollusk shells were made u n e v e n t fully, but w h e n scientists began measuring t h e temperature of inoceramid shell material, they got a profound shock. T h e temperatures found in these shells were always very high compared to those of o t h e r shells in t h e same deposits. Inoceramid shells from Sucia Island, for example, yielded a temperatute of 95°F! T h e only places on earth w h e t e o n e finds such h o t sea water are right at the surface at t h e equator a n d in restricted lagoons and salt marshes. Sucia was tropical, t h o u g h n o t t h a t tropical, according to most indicators. Analysis of the o t h e r clams and shells from Sucia suggested t h a t its sediments were deposited in fairly shallow water, perhaps 50 to 100 feet deep at most. Perhaps—just possibly—the water could h a v e b e e n t h a t warm. But a greater surprise was yet in store. Isotopic analyses of inoceramid shells collected from very deep-water sediment showed similarly high readings. 199

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T h e r e was no possibility t h a t these large inoceramids, such as t h e forms on Gabriola Island, lived in such shallow water. Unless . . . Unless t h e giant clams did not live on t h e cold b o t t o m at all but fell there only after d e a t h . In t h e 1980s a new hypothesis was proposed: Inoceramid bivalves were a t t a c h e d to floating logs, and all those found in various deep-water deposits had arrived t h e r e only after they died. T h e r e seemed to be no o t h e r way to explain t h e isotopic results, and many serious scientists subscribed to the "floating inoceramus" theory. In the late 1980s, two of my graduate students advanced a n o t h e r idea. In a paper published in t h e journal Geology, Ken MacLeod and Kathryn H o p p e , after analyzing inoceramid shells collected from deep-water cores in Europe, suggested t h a t t h e inoceramids formed their shells in a way t h a t excluded t h e isotope oxygen-18. T h i s led to spurious results w h e n t h e values were converted to temperatutes using t h e m e t h o d s of Urey. T h e inoceramids were not living in 95°F water, but their shells wete painting that picture t h r o u g h what was described as a "vital effect." S u c h vital effects were n o t u n p r e c e d e n t e d . T h e y are also k n o w n from living corals, w h i c h harbor a tiny plant in their flesh t h a t aids in formation of t h e skeleton. T h e presence of this microscopic alga in t h e coral's flesh also reduces t h e a m o u n t of oxygen-18 incorporated into the coral's skeleton, and this yields an anomalously high p a l e o t e m p e r a t u r e reading. Yet corals live only in very shallow seas, for t h e symbiotic algas in their flesh need warm water and light. T h e deep-water inoceramids could not possibly be harboring such shallow-living symbionts. S o m e t h i n g else had to be involved.

H y d r o t h e r m a l v e n t s and "cold s e e p s " T h e answet came from a completely c h a n c e discovery: that of hydrothermal v e n t faunas in the modern-day deep sea. On February 17, 1977, the submersible ALVIN was diving on a mid-ocean ridge deep in the Pacific O c e a n . T h e s e are t h e regions where n e w sea floor is produced. O c e a n o g r a p h e r Tjeerd v a n A n d e l , w h o was on this historic dive, described the discovery as follows: 200

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W h e r e a s t h e ocean floor at this d e p t h [2500 meters] tends to be rather poor in organisms large e n o u g h to be seen f r o m the ALVIN, t h e spring [a h o t , volcanic water seep] seemed to be a veritable garden or aquarium full of large life forms. W h i t e clams, mussels, large

white crabs resembling those of

coastal

tide

pools,

wotms with featherdusters living in calcareous tubes were everywhere. T h e n u m b e r of animals, t h e total a m o u n t or biomass, seemed far, far larger t h a n a n y t h i n g ever seen on t h e deep sea floor. Moreover, most of t h e animals did n o t resemble t h e deep sea

kind

sea cucumbers,

anemones,

shrimp—at all, but rather

reminded me of the fauna of a coastal tide pool. On t h e first dive I was especially struck by t h e white clams with e n o r m o u s shells measuring up to 20 cm in length; we later found t h e m to weigh several pounds each. (Van A n d e l , 1977, pp. 1 4 9 - 1 5 0 )

All of this newly discovered "vent fauna" lived well below t h e zone of plankton, just like t h e inoceramids of t h e Cretaceous. T h e v e n t fauna, a n d faunas discovered soon after in regions of cold m e t h a n e seeps (areas where cold, m e t h a n e - r i c h water comes up t h r o u g h t h e sea floor), used an entirely different energy source t h a n sunlight for t h e base of their food chains. T h e y used m e t h a n e gas. T h e discovery of deep-sea v e n t faunas revolutionized n o t only biological oceanography but in a significant way paleontology as well. Hydrothermal vent and cold seep-faunas (where animals cluster around natural gas, cold brine, or petroleum seeps) are diverse and rich in life in places where life is normally sparse and rare. T h e discovery of h y d r o t h e r m a l v e n t c o m m u n i t i e s in t h e late 1970s alerted biologists to t h e presence of significant associations of " c h e m o a u totrophic" organisms on t h e sea floor—organisms t h a t use as their primary energy source n o t sunlight but o t h e r types of energy. By t h e 1980s it was realized t h a t two distinct associations of animals are present: h y d r o t h e r m a l vent faunas and "cold-seep" faunas. C o l d seeps are found in a variety of volcanic areas and over organic-rich sediment accumulations. Cold seeps produce 201

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a very peculiar type of sediment formation; they produce limestone bodies in sediment where limestone is usually absent. T h e y also c o n t a i n a fauna different from t h a t in t h e surrounding sediment. Present-day h y d r o t h e r m a l vents and cold seeps are characterized by localized c o n c e n t r a t i o n s of hydrogen sulfide and/or m e t h a n e - r i c h fluid that are generated and t h e n expelled o n t o t h e sea floor. At these sites, high densities of c h e m o a u t o t r o p h i c bacteria t h a t live on m e t h a n e occur in suspended ventfluid emissions, or as bacterial symbionts enclosed within invertebrate tissues, or e v e n as free-living surface mats. T h e c h e m o a u t o t r o p h i c bacteria oxidize t h e vent-seep fluids to produce metabolites and energy at the base of a c h e m o s y n t h e t i c food c h a i n . T h e s e v e n t fluids mix with sea water to form localized and often anomalous sedimentary precipitates t h a t include metallic sulfides and barite, a n d isotopically distinctive carbonates. Many of the organisms adapted to these areas live in e n v i r o n m e n t a l conditions t h a t would prove toxic to most marine organisms. T h e recognition of v e n t a n d cold-seep localities in t h e ocean floor caused paleontologists to re-evaluate t h e origin of numerous anomalous rock and faunal associations. Most troubling had been the presence of isolated limestone bodies in deep-water sandstone or turbidites. T h e s e had long been interpreted as shallow shoals or fossiliferous blocks transported to deep-water settings. T h e fossil fauna within these limestone bodies was quite different from faunal elements found in the surrounding matrix, just as it is in modern cold-seep areas. T h e final peculiar characteristic of these limestone bodies was their isotopic composition. T h e y yielded isotopic readings typical of very warm water, w h e n in fact they formed in water near t h e freezing point. Limestones in m o d e r n seep deposits, just like t h e shells of the a n c i e n t inoceramids, give a false picture of their temperature of formation. T h e fauna of such cold seeps are n o w k n o w n to be highly distinctive in b o t h their recent incarnations and t h e distant past. Most c o m m o n and p r o m i n e n t members of e x t a n t cold-seep c o m m u n i t i e s are large clams and mussels with bacteria in their flesh t h a t enable the clams to live off m e t h a n e in the surrounding sea water rather t h a n off p l a n k t o n , like most other clams.

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Tube worms and specialized gastropods are present as well. O n e of t h e most striking aspects of t h e cold-seep bivalves is their large size. T h e bivalves found in the seeps are normally several times larger t h a n any bivalves found in the surrounding, n o n - s e e p deposit sediment. Since these early discoveries, a variety of cold-seep faunas, mainly of Mesozoic and Cenozoic vintage, h a v e b e e n identified in t h e geological record. Yet research into m o d e r n and a n c i e n t cold-seep accumulations is still in its infancy. To date, research efforts h a v e b e e n largely observational; we have little or no theory from w h i c h to predict t h e geographic p l a c e m e n t , biological makeup, or temporal d u r a t i o n of these deposits. A large number of cold-seep regions h a v e now been identified. Many are associated with deep-sea plate t e c t o n i c settings, a l t h o u g h they also occur on the margins of c o n t i n e n t s , at t h e base of underwater cliffs, and at oil and gas seeps on the c o n t i n e n t a l slope. T h e fauna surrounding vents and seeps is normally characterized by an unusual taxonomic assemblage. Some researchers have proposed that vent/seep faunas are long-lived groups composed of many relict taxa of great geological antiquity. This implies that vent/seep faunas have been largely immune to the mass extinction events that have so profoundly affected the rest of our planet's biota. If so, the vent/seep fauna may be the most insulated group of animals on earth from mass extinction events, being largely self-sufficient except for a need for oxygen. This fauna might be able to survive even catastrophic meteor impacts and other planetary calamities. Vent and seeps may thus be important faunal reserves or refuges, "lost worlds" retaining archaic forms. An important and still unresolved question is whether the vent/seep areas are also seed stocks for evolutionary innovation and planetary repopulation following a mass extinction event. Are these faunas units of evolutionary innovation, where new types of life first atise? Are they regions of relict taxa? A r e they sites impervious to mass extinction, and therefore storehouses of diversity? Fossil cold-seep areas are most c o m m o n l y recognized from Tertiary deposits. Far fewer h a v e b e e n recognized from Mesozoic deposits, and only small n u m b e t are yet recognized from Paleozoic deposits. Verena Tunnicliffe

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of t h e University of Victoria, a specialist on this fauna, has proposed that t h e vent/seep c o m m u n i t i e s first arose in t h e middle Paleozoic, although this theory has n e v e r b e e n rigorously tested. Cold-seep deposits dating from the early Paleozoic a n d oldet are still p r o b l e m a t i c . T h e inoceramid clam accumulates are surely related to cold seeps. 1 surmise t h a t they were clams t h a t housed symbiotic algas or (more probably) bacteria and lived preferentially in areas of t h e sea b o t t o m whete m e t h a n e gas was being released. T h e fact t h a t so many regions of t h e Cretaceous oceans seem to h a v e b e e n colonized by inoceramid clams, presumably all living on m e t h a n e , tells us s o m e t h i n g fascinating about t h a t long ago time. T h e oceans t h e n were clearly different in chemical structure. T h e y were far less h o m o g e n e o u s , they were m o t e turbid, a n d they retained organic material in sediment to a far greatet degree t h a n now. T h e pristine inoceramid beaches of G a b r i o l a Island h a v e given us a priceless glimpse i n t o t h e d e e p p a s t — t h a n k s to an isotopic time m a c h i n e or two.

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The

Part

Four

Time

Machine

10

Cretaceous

Park

W e h a v e come a long way, i n space and time, t h r o u g h t h e use o f t h e various time machines profiled in this book. Fossil, radiometric and magnetic dating machines; t h e d e t e c t i o n of a n c i e n t latitude, sea level, and temperature; the reconstruction of fossils and t h e c o m m u n i t i e s they lived in. Yet there are so many more invaluable techniques t h a t we h a v e n o t e v e n touched up here. How to summarize? Perhaps t h e best way to recap t h e discoveries, reinterpretations, and e v e n speculations t h a t this book recounts is to recreate ancient Sucia Island in a story, using t h e disparate facts we h a v e u n e a r t h e d as the backdrop. To do t h a t I'll use o n e of science fiction's favorite devices, an "actual" time m a c h i n e . 207

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Physicists, the top carnivores of t h e trophic pyramid of scientists, have at their service t h e most expensive m a c h i n e s and instruments ever devised. To smash atoms, to find and identify t h e smallest particles in the universe, to see a n d measure t h e last whispers e m a n a t i n g from t h e Big Bang—such quests require brute instrumental strength. Nevertheless, physicists still routinely e n c o u n t e r p h e n o m e n a and questions t h a t are beyond the scope of even the most advanced technology. W h e n this h a p p e n s they must take an entitely different t a c k — a n approach t h a t may n o t solve a problem but t h a t at least brings it to an intellectual p o i n t where it can be re-examined and perhaps can eventually be solved theoretically rather t h a n experimentally or observationally. T h e s e exercises are "thought

experiments." Einstein loved

t h o u g h t e x p e r i m e n t s — a n d needed t h e m . Yet these devices are not the sole property of physicists. Scientists in o t h e r disciplines (such as paleontology) c a n use t h e m too. Every time a paleontologist attempts to reconstruct conditions in some long-ago time, he or she is c o n d u c t i n g a t h o u g h t experiment. O u r c o n c l u d i n g c h a p t e r is science fiction, of course, and so is sure to incite t h e wrath of those w h o cringe at any b e n d i n g of the unspoken rules gove r n i n g c o n t e n t in "trade science books" (books written, in other t h a n a textbook format, for people w h o love science). But, as t h e preceding chapters will bear witness, t h e science in t h e following science fiction comes from many years of dogged detective work by many different scientists. W h a t follows is a t h o u g h t e x p e r i m e n t of sorts, for it is t h e best guess I can make, on the basis of t h e evidence, about what a true time-travel expedition back to t h e locality of Sucia Island in t h e Late Mesozoic world would encounter.

June

15, 2 2 2 2

T h e device sat gleaming under sterile fluorescent lights. It looked rather like a boat, instead of w h a t e v e r a time m a c h i n e is supposed to look like. A n d that was a good thing, actually, given t h a t its prime purpose after time-traveling to t h e Late C r e t a c e o u s Pacific O c e a n , just off the western coast of N o r t h A m e r i c a , was to float reliably for three hours in a long-ago sea.

2 OS

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T h e event itself was easy: O n e m o m e n t t h e operator was in his o w n time, sitting in t h e cockpit with all of his gear piled around h i m , and the next he was bobbing on t h e surface of an a n c i e n t sea. His first look was instinctive: T h e n u m b e t s on t h e c h r o n o m e t e t — t h e record of h o w far back into time he had traveled—stared back at h i m . His o w n t i m e was such a low n u m b e t fot such an old p l a n e t — t o measure time in t h e n u m b e r of years since the birth of a m a n seems ignorant of h o w vanishingly brief has b e e n our h u m a n sojourn on earth, but a system of t i m e m e a s u r e m e n t built on historical precedent is an intractable master. H e n c e t h e date on t h e console read - 7 6 , 6 0 0 , 0 0 0 ± 100,000: seventy-six million years before his time. To t h e right of these numbers were t h e o t h e r displays, based on o t h e r types of time keeping. T h e first display was marked G e o m a g n e t i c Polarity Time Scale: It read m a g n e t o c h r o n 33R, which told the operator t h a t he was in t h e first magnetic reversal after t h e C r e t a c e o u s long-normal interval. T h e display marked Biostratigraphy Time Scale was subdivided into European Standard, Western Interior, and Pacific Coast columns and was designed to indicate t h e names of the stages and fossil zones. T h e y read C a m p a n i a n Stage: Bostrychoceras polyplocum Zone, Baculites scotti Zone, and Baculites inornatus Zone, t h e zones being n a m e d after t h e diagnostic fossil a m m o n i t e s found in Europe, the interior of N o r t h America, and the Pacific Coast of N o r t h A m e r i c a , respectively. At t h e fat right, t h e i n s t r u m e n t panel listed t h e sea level indicator: Global sea level sequence H i g h s t a n d 22. He stared at this panoply of measurements of time, as recorded by years, m a g n e t i c reversal stratigraphy, fossils, and t h e very level of t h e sea itself in its global basins, trying to decide whether he felt any older, h a v i n g b e c o m e the first h u m a n on earth. Yet the mishmash of numbers and letters only elicited a wry chuckle, for h e , n o w Master of all Time, was still its slave: Enmeshed in time's various reversible threads was the most inexorable timekeeper of all, t h e wholly finite and utterly d e t e r m i n a t e n u m b e r of heartbeats measuring his o w n life—a stream that could never to be reversed. T h e repetitive c o m m a n d s of long training took over, and he found himself pulling out t h e inflatable buoy with its line and anchor. He watched

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himself, as if from a remote distance, setting t h e huoy with its bright strobing beacon. T h e a n c h o r snagged quickly, telling h i m t h a t he was in shallow water, just as the planners had promised. His insertion point (and he certainly hoped, his removal point as well) was n o w marked in this sea, and at last he could look around on this fine afternoon, late in the Cretaceous Period. First impressions: Land was visible nearby, perhaps a h u n d r e d yards off; it was green and lush, with tall trees a n d a thicker understory. T h e odor of fetid jungle a n d o t h e r things u n k n o w n to h i m thrust t h r o u g h t h e scent of the sea; t h e very air was a miasma of pines, flowers, swamp, m e t h a n e , saurians, and a t h o u s a n d o t h e r Mesozoic perfumes no m a n before had ever smelled. He breathed deeply of this C r e t a c e o u s air, b o t h attracted and repelled, and felt—or imagined he felt—immensely invigorated. He pulled out a small bottle, opened it to t h e air around h i m , a n d t h e n sealed it, a first sample. He looked o n c e more towatd land and saw a faint surf painting white streaks on the distant beach. F a t t h e r inland stood high m o u n t a i n s , and one of t h e m trailed a t h i n p l u m e of black smoke and ash, t h e atmospheric signature of an active v o l c a n o . Yet these were but t h e briefest of impressions before a new sight captured his a t t e n t i o n . M o v e m e n t caught his eye, and he stared up into a sky full of w o n d e r — w i n g e d wonder—for above h i m wheeled great apparitions of scale and fur, t h a t could only be pterosauts. T h e s e bat-like creatures, someh o w simultaneously monstrous and benign, were flying—not gliding— majestically overhead, with many smaller reptilian and avian fliers moving more rapidly a m o n g t h e m . He was amazed at t h e size of t h e larger reptilian aviators; it was as t h o u g h small airplanes had b e c o m e sentient and now navigated t h e sky unfetteted by h u m a n constraint. His small boat bobbed in the swell, and our time traveler marveled as t h e great and small fliers skimmed t h e surface for fish, or dived h e a d l o n g into t h e sea, like great pelicans at play in a hallucinogenic airshow. "It would be good just to float h e t e , " he t h o u g h t , "offshore of this Mesozoic land, and simply w a t c h t h e aetial circus above." But he had been a diver for many years, and always t h e internal clock was ticking, whispering in his

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ear about time passing; this voyage nearly 80 million years into t h e past was like a scuba dive: borrowed time in a foreign world. He h a d work to d o . T h e first observation was t h e quickest, a l t h o u g h he found t h a t taking a latitudinal measurement with a sextant in a rocking boat was trickier t h a n he had anticipated. Nevertheless, he shot a crude solar. He didn't need great precision, for t h e n u m b e r he recorded only confirmed what his first view of the sun had already told him: He was at a low latitude, surely t h e tropics, somewhere between 25 and 30 degrees n o r t h . Nearly 80 million years h e n c e , this place, which would be n a m e d Sucia Island by an e i g h t e e n t h - c e n t u r y Spanish explorer, would be marked on t h e first charts of t h e region at 49 degrees n o r t h . Between t h e e n d of t h e C r e t a c e o u s and t h e emergence of Homo sapiens some 65 million years later, Sucia Island a n d all of its surrounding territory would travel more t h a n 2000 miles n o r t h ! He glanced at his checklist and began preparing for t h e dive. T h e twin80 tanks felt marvelously light in their t i t a n i u m casings, and he decided to wear the thinnest wet suit after measuring t h e surface water temperature and finding it to be a balmy 89°F, compared with readings of less t h a n half t h a t in his time. He looked around o n c e more, tasted twenty-third century air as he sucked from his regulator, and rolled into t h e sea.

A n a n c i e n t sea b o t t o m A lurch and a loud splash, t h e usual m o m e n t a r y vertigo while he somersaulted, and t h e n he bobbed toward t h e surface. T h e water was turbid, filled with great clouds of p l a n k t o n . He was anxious to get d o w n below this murky surface, for in his world t h e surface regions were patroled by large carnivorous hunters, such as t h e sharks, and he had no d o u b t t h a t this world's larger carnivores, which included mosasaurs and elasmosaurs as well as sharks, were far more dangerous t h a n a n y t h i n g of his time. He made a final check of his gear, zeroed his watch, traded snorkel for regulator, and slid d o w n into t h e late Mesozoic ocean.

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U n d e r n e a t h t h e sea's turbid surface layer visibility improved, and our time traveler was relieved to see t h e dim outlines of t h e bottom, far below. He had never liked vertical descents, especially in very deep or murky water where you lost sight of b o t h t h e surface and t h e b o t t o m . He swam down quickly, chased by beams of s h i m m e r i n g sunlight, through a cerulean-blue water c o l u m n rich in tiny invertebrates and m i n n o w s , and he t h o u g h t of the h u n d r e d new species he was surely passing by. N o w t h e b o t t o m was visible, coming up fast, and he gently dropped d o w n o n t o its sandy surface, landing on his knees, to be surrounded like a dream by a Mesozoic sea b o t t o m fest o o n e d with multicolored algas: bright, current-wafted p e n n a n t s in browns, yellows, reds, and greens. But his eyes ignored t h e submarine flora; he searched instead for old friends he had k n o w n only in death. He quickly saw t h e m in legions, quite alive, and he greeted t h e m with t h e hoots of joy t h a t are t h e only underwater e x c l a m a t i o n of a scuba diver. T h e sandy b o t t o m was slightly rippled, barely disturbed by the stronger waves at t h e surface. T h e tubular, tentacled necks of clams whose shells were deeply buried in t h e fine sand were scattered across the b o t t o m in great n u m ber, and he wryly wondered w h a t a c h o w d e r of these Cretaceous clams would taste like. Snails large and small crawled by, leaving irregular tracks across t h e sediment surface, while circular sea urchins rattled their pike-like spines a m o n g t h e immobile i n h a b i t a n t s : t h e sponges, bryozoans, and hydrozoans and a myriad of o t h e r colonial and solitary filter-feeding animals living in their skeletal mansions and t e n e m e n t s . But of all the creatures visible, o n e stood out. T h e b o t t o m was littered with large clams b o t h dead and alive. T h e s e C r e t a c e o u s clams were distant relatives of t h e oyster and perhaps the most ubiquitous residents of t h e Late Cretaceous seaways. By the end of the Cretaceous Period, 65 million years before t h e time of h u m a n s , they would be entirely e x t i n c t . But on this older sea b o t t o m they were everywhere. T h e y sat atop t h e sediment, n o t buried in it like t h e o t h e r species of clams hete, and their large, ribbed shells were crowded with colonies of encrusting invertebrates. Bright m a n t l e flesh e x t e n d e d partly over the inoceramid's shells, making t h e m look like t h e giant clam Tridacna of m o d e r n coral reefs, and probably for the same reason, he t h o u g h t : Tridacna clams harbor gardens of 212

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symbiotic, single-celled p h y t o p l a n k t o n in their flesh, w h i c h aid in respiration and shell formation. M a n y scientists t h o u g h t t h a t the inoceramids used the same

trick, or perhaps

they

used bacteria

instead.

"We shall

see,"

he told

himself. He took a small sample of t h e sediment and t h e n placed an entire inoceramid, shell and all, in t h e large p o u c h sewn into his buoyancy c o m p e n sator. W i t h these samples packed away, he shoved off t h e b o t t o m , taking photos with his camera as he rose, t h i n k i n g of t h e papers t h a t would he written about these clams and t h i n k i n g of o t h e r things: his air supply, the d e p t h , the time, and the o t h e r animals he needed to find. T h e dive was a great mix of t h e u n k n o w n and t h e familiar. T h e sandy b o t t o m was like many he h a d seen before, in his o w n time. T h e fields of clam necks, t h e tropical mollusks and e c h i n o d e r m s — m u c h of what he saw h a d a perfectly modern appearance. But o t h e t things, such as t h e inoceramids and the partly buried trigoniid clams, were foreign—anomalies t h a t were jarring to his trained eye. T h e y were so out of c o n t e x t . T h e y should be fossils in an outcrop, n o t loosely scattered on this b o t t o m , n o t so obviously alive. He powered on, his large fins and steady kick carrying h i m rapidly over fertile fields of t h e clam-rich community. He decided to descend furthet and began to follow the sloping b o t t o m into deeper water, looking for those creatures he had so long dreamed about and so long studied, t h e Mesozoic swimming shellfish called a m m o n i t e s . He knew what they ought to look like. S o m e had shells like great wagon wheels with the body of a squid stuffed inside ("Perhaps*." he told h i m self) or, more probably, like t h a t of t h e c h a m b e r e d nautilus of his o w n time, the last remaining m e m b e r of t h e long-lived group of n o w largely e x t i n c t cephalopods to which t h e a m m o n i t e s belonged. O t h e r s had evolved more ambiguous shapes—some straight, some like snails, some like candy canes, some like the mess a child makes with a capless tube of t o o t h p a s t e — a n d no scientist knew what these uncoiled forms did for a living or e v e n h o w or where in the ocean they lived. A b o u t t h e mystetious a m m o n i t e s only o n e thing was certain: All of t h e m , irrespective of shape, died out in the same great catastrophe that killed t h e dinosaurs, a calamity brought about by the 213

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dire e n v i r o n m e n t a l effects immediately following the collision of a large c o m e t with our planet, some 65 million years ago—a calamity that set the stage for a new suite of creatures on land and sea to vie for d o m i n a n c e . But here on this quiet b o t t o m , with t h e sunlight from the sea's surface 50 feet overhead m o t t l i n g t h e sandy b o t t o m and its late Mesozoic inhabitants with faintly visible patterns, t h a t catastrophe was still 12 million years in t h e future, and a m m o n i t e s and their Mesozoic world were in fine fettle. He had already seen in t h e sand shell fragments t h a t he suspected were from a m m o n i t e s , a n d if he couldn't find any living specimens, these would have to do. T h e r e were too many questions waiting to be answered for h i m n o t to bring h o m e s o m e t h i n g of these enigmatic animals, e v e n if it was only fragmentary shell material from long-dead specimens. But the living could answer far more questions t h a n t h e dead, e v e n t h e recently dead, so he swam onward, searching. A h e a d , emerging from t h e gloom, he saw a new feature: what appeared to be a large m o u n d of rock. Yet, as he moved closer, he saw t h a t the "rock" moved ever so slightly in t h e swell, belying its lithic appearance. W i t h a start he realized t h a t he was looking at a carcass of rotting flesh and disarticulating bones, a once-large m a r i n e r e p t i l e — a n elasmosaur?—now transformed into a submarine feeding station. It was t h e focal point for a diversity of scavengers and carrion eaters. Sharks swam a m o n g the bones, worrying slabs of flesh off t h e rib cage, while smaller fish nipped at gray carrion. Some areas of t h e carcass were nearly covered with crabs and snails, scavengers cloaked in a carnival of shape and color. T h e sharks looked quite familiar, as did the crabs, but many of t h e snails were strange to h i m . T h e s e o r n a t e creatures had ribs and knobs like those found today only a m o n g tropical mollusks, but they were members of species no longer alive. He moved closer, wary of t h e sharks ( w h i c h looked just like those of his world), and as he did so, a new side of t h e carcass came into view. U p o n seeing t h e new suite of animals feeding there, he felt a great t h r o b of joy, for a m o n g t h e busy scavengers were several old friends, creatures still alive in the modern-day tropical Pacific: pearly nautiluses. Two large adults and several

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juveniles belonging to at least two species chewed on a large h u n k of flesh, and he could hear t h e sound of their heavy beaks rasping on a bone's edge. He had expected to see nautiloids, but he had n o t expected t h e m to seem identical to t h e nautiloids of his world. S o m e w h e r e in time, he thought, Eldredge and G o u l d must be s m i l i n g — a n d Darwin rolling over in his grave. T h e s e species would n o t c h a n g e in any appreciable fashion for more t h a n 80 million years. T h e y would survive so m u c h , including t h e impact of t h e c o m e t t h a t spelled t h e dinosaurs' demise. T h e y would b e c o m e "living fossils," persevering u n c h a n g e d . But this species of the genus Nautilus would also give rise to a whole slew of n e w species in t h e aftermath of the impact event t h a t ended t h e Age of Dinosaurs. He moved in closer to t h e oblivious nautiloids and pried o n e away o n e from its meal. In color and shape it seemed identical to Nautilus pompilius, the familiar Nautilus found in the Philippines, Fiji, Australia, N e w G u i n e a , and Samoa and on a t h o u s a n d smaller islands and rocky reefs across a huge expanse of t h e Indo-Paciftc. He let it go, and it turned back toward its meal, tentacles e x t e n d i n g outward. His t a n k was n o w nearly half empty, a n d he had not glimpsed t h e quarry he had traveled so far to see. W e r e t h e ammonites restricted to far deeper water t h a n he could visit? T h e i r fossils were c o m m o n e n o u g h in t h e sedimentary strata of t h e future Sucia Island deposits, yet here, on this b o t t o m t h a t was to b e c o m e those sedimentary rocks, he saw few of their shells, and he saw n o n e alive. He again followed t h e sloping sea floor into greater depths, and as he did so, t h e creatures on t h e b o t t o m c h a n g e d . As t h e sediment became finer, the n u m b e r of burrowing clams greatly diminished, as did t h e n u m b e r s of snails and other creatures t h a t he had seen living atop t h e sediment. T h e fine mud at this 100-foot d e p t h was streaked by a diversity of markings and trails left by vermiferan life forms; here and there a slow-moving sea cucumber or toiling crustaceans also could be seen. T h e only shelled creatutes were the ubiquitous flat clams, t h e inoceramids, but e v e n they were reduced in number. In the distance he saw a n o t h e r nautilus, and he marveled anew at how m u c h they looked like others of their kind t h a t he had trapped in the

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Philippines, N e w G u i n e a and Fiji and had dived with at night in the cool water outside t h e great N e w C a l e d o n i a n barrier reef, the only place on earth in t h e A g e of H u m a n i t y where nautiluses could be seen in the d e p t h ranges of a scuba diver. But in those places, t h e nautilus lived on t h e deep fore-reef slopes, t h e muddy d e p t h s in front of coral reefs. Here they inhabited a completely different e n v i r o n m e n t . He had n o t seen any coral at all, and despite the w a r m t h of t h e seas, t h e r e were no reefs. A n o t h e r mystery a m o n g many. In spite of t h e bright sun he knew to be shining far above, he was now gliding t h r o u g h a twilight world, a dim smoky topaz of clarity but little light. Yet it was by no m e a n s silent: T h e snapping and crackling of crustaceans in thousands of burrows around h i m produced a c h a o t i c percussive symphony. T h i s was his only c o m p a n y as he glided ever deeper, and he felt very, very a l o n e — t h e only h u m a n on t h e planet, t h e only m a m m a l larger t h a n a squirrel. T h e water became clearer a n d colder as he passed through a t h e r m o cline. N o w he could see for m a n y tens of yards in all directions. A h e a d of h i m , t h e greater depths of t h e slope he descended yawned like a dark night b e c k o n i n g . A large shape looming to his right startled h i m , and it resolved into a slim shark following its o w n agenda, passing through the sea whips and sea fans encrusting t h e rare rocks and larger shells t h a t offered anchorage amid t h e pocked and burrowed mud. A school of small lobe-finned c o e l a c a n t h fishes fled before t h e shark and t h e n resumed their own h u n t i n g .

A n old friend He reached 150 feet, his m a x i m u m d e p t h limit on this dive, and now his air supply a n d his body's nitrogen uptake became primary concerns. But those worries vanished instantly as a small forest of objects resembling sticks and large pencils descended to t h e sea floor about 10 yards to his right. He was mystified; t h e r e was n o t h i n g in his long diving experience to compare with t h e sight. He c h e c k e d his camera settings, turned the camera strobe to maximum power, a n d glided toward this curious apparition, uncertain what these creatures were, but unafraid. He approached t h e nearest of the sticks and saw 210

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that it was n o t wood but rather was composed of a long, tapering cone-like shell, with many t h i n tentacles e x t e n d i n g outward from t h e oval o p e n i n g at its b o t t o m . T h e tentacles attached to a tubercular head adorned with fleshy tidges and two large, u n b l i n k i n g eyes recalling H. G. Wells's vision of Martians. But these were n o t Martians. T h e y were earthlings of long standing t h a t first evolved in t h e D e v o n i a n Petiod, some 400 million years before h u manity. T h e y were a m m o n i t e s , in this case straight-shelled forms, t h e ubiquitous Baculites inomatus, by far t h e most c o m m o n (and diverse) a m m o n i t e s of the late Cretaceous seas. He glided in close to t h e nearest baculite. Its shell was about a foot long, and the creature and shell were oriented in a nearly vertical position in the sea, perpendicular to t h e b o t t o m , with t h e head and tentacles facing the b o t t o m while the sharply tipped apex of t h e straight shell pointed toward the surface far above. H e r e was a creature t h a t lived an entirely vertical existence, rising or falling in t h e water c o l u m n but h a v i n g little ability to swim laterally. Its very design suggested speed, but speed upward, and he guessed that these a m m o n i t e s responded to threats by quickly taking flight in t h e unexpected vertical direction. He knew this particular species well. It was an old a c q u a i n t a n c e t h a t he had found as fossils in so many places of his world: t h e S a c r a m e n t o and San Joaquin Valleys of California, Baja California, C o l o r a d o , S o u t h Dakota, and even farther afield, in Madagascar, S o u t h Africa, and C h i l e . H e r e it was o n e of a large school, busily rooting t h r o u g h the soft sediment with its tentacles. Occasionally it would find some crustacean morsel, and pass it to a m o u t h located in the center of the tentacles. O u r time traveler thought it o n e of t h e most beautiful animals he had ever seen. It was not like a Nautilus at all; it gave n o n e of the impression of stupidity and lassitude that set the nautiloids apart from the rest of the cephalopod clan. It was much more akin to the most advanced and beautiful squid imaginable, and the streamlined c o n e of its shell only e n h a n c e d this sense of modernity, not antiquity. He had seen a thousand of its fossil shells, but somehow the living creature was a revelation, like the first view of Saturn or Jupiter through a good telescope. Pictures—and fossils—simply did not do justice. 217

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He watched a play of c h r o m a t o p h o r e s on the haculites's head region— shivers of color passing from tentacles to head, increasing in strength and h u e w h e n a particularly large crustacean was found. He came closer, and the creature remained ohlivious, or indifferent, to his presence. He was now only inches away, lying p r o n e on t h e soft sediment, watching this a n c i e n t organism feed, o n e of h u n d r e d s similarly engaged on this muddy h o t t o m . He tried to peer i n t o t h e m a n t l e cavity and felt almost like a voyeur, but he had to know. " H o w many gills? W h e r e ' s t h e ink gland? W h a t does t h e septal mantle look like? H o w does it m a k e its intricate and florid sutures, among the most complicated sttuctures ever produced by nature? A n d what are the sutures for?" He swung t h e N i k o n o s underwater camera with its flash unit around, centered t h e nearest baculite in his viewfinder, and shot pointblank at t h e long, t h i n a m m o n i t e . T h e flash, a d e t o n a t i o n of light in this near-darkness, precipitated the most amazing spectacle. A h u n d r e d slim cones blasted off t h e b o t t o m as one, the e n t i t e school streaking up in concert, leaving a great trail of black ink in their wake, and thus looking for all t h e world like an ICBM strike in progress. He watched t h e m rise to 20 or 30 feet above the hottom. T h e r e they slowed, finally h u n g motionless in t h e water column, and t h e n began sinking slowly back d o w n to t h e b o t t o m , still vertical, a h u n d r e d rockets fotgetting their fright, r e t u r n i n g to their launching p a d s — a n d feeding grounds. He savored t h e sight and shivered with pleasure, or was it t h e invading cold? T h e cold was a wake-up call; it was clearly time to go. He rose up with his bubbles, carefully following t h e smallest and slowest, ascending into warmer and brighter water, a n d soon n e i t h e r t h e b o t t o m nor t h e surface was visible. He ascended in this c o c o o n , watching jellyfish, small herring, and o n c e a compressed, planispiral a m m o n i t e swimming just at the edge of visibility. N e a r t h e 30-foot level he began hearing sharp cracking noises, and he pirouetted to scan t h e water a r o u n d h i m . He was surprised to see powdery and c h u n k y white and brown material falling a t o u n d h i m . A larger piece cartwheeled downward several yards away, and he interrupted his ascent to swim after the falling material, c a t c h i n g it at a d e p t h of about 40 feet. It was 218

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the size of a d i n n e r plate, with irregular edges. O n e side of t h e fragment gleamed silvery in the shafts of m u t e d sunlight d a n c i n g d o w n from the surface, and he saw t h a t its o t h e r side was creamy white, with a large reddish stripe traversing o n e corner. T h e r e was no mistaking this shell. S o m e w h e t e above h i m , a large a m m o n i t e had just died. He dropped the piece of shell a n d warily rose to 20 feet to start his decompression stop, slowly turning 360's in lookout. During his second or third rotation he saw a distant school of creatures c o m i n g in his direction. As they approached through the shallow surface turbidity, he recognized t h e m as planispiral a m m o n i t e s , species with large discoidal shells, all swimming backwards with head b e h i n d . S o m e had shells more t h a n a yard in diameter, and all were countershaded: dark color on top of t h e shells, white b e n e a t h , a camouflage evolved because it fools predators either above or below. Pachydiscids, he thought, seeing t h e distinctive ribbed shells. T h e y swam slowly but purposefully, conveying a sense of power, like old battleships passing in stately formation. T h e y were n o t like t h e skittish, torpedo squids of his day, which relied on speed to save their u n p r o t e c t e d and succulent bodies from becoming meals. T h e a m m o n i t e s used their shells like a n c i e n t dreadnoughts, a streamlined but massive armor. He could n o w see their large, octopus-like eyes as they passed by, t h e closer animals veering to avoid h i m , the farther reaches of t h e school paying h i m no heed. He watched the last of t h e large a m m o n i t e s swim lugubriously into t h e distance, finally to disappear, swallowed by t h e sea as they left his 50-foot circle of visibility. He was nearing t h e e n d of his first decompression stop, and as he watched t h e second h a n d on his c h r o n o m e t e r sweep its slow arcs, m o v e m e n t caught his eye. He saw a n o t h e r school of large a m m o n i t e s just at the limit of visibility, and o n c e again he heard a piercing crack. He began to swim toward this second school, t h e bright sunlit water warming his body. T h e a m m o n i t e s were careening and scattering as he approached, and now he could see a larger, wraith-like shape a m o n g t h e m . He backpedaled as he watched the mosasaur feeding a m o n g t h e a m m o n i t e s . It was relatively small, only about 8 to 10 feet long, and its shape and head were quite familiar to h i m . He was well acquainted with t h e m o n i t o r lizards of Pacific islands 219

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in his time (a 3-footer had o n c e crawled into his bed on an island on Australia's G r e a t Barrier Reef), and he h a d e v e n seen a K o m o d o dragon, the largest lizard of his world and found only on a r e m o t e island in Indonesia. But e v e n t h e K o m o d o dragon, w h i c h could reach a length of 8 feet or more, was puny compared to t h e more massively built and far longer mosasaurs, which could reach a length of 30 feet. Yet the mosasaurs were close relatives— direct ancestors, really—of those future lizards, and although of dinosaurian dimensions in some cases, they were simply lizards grown giant. But theit feet h a d evolved into paddles, and their tails had broadened into a large, flattened shape more resembling t h a t of a crocodiles t h a n the long whip-like tails of its terrestrial relatives. He watched it swim, admiring its speed and agility; in its e l e m e n t , the mosasaur reminded h i m of t h e large seagoing crocodiles he h a d seen in Micronesia, creatures far more dangerous to h u m a n s t h a n any shark ever evolved. A l t h o u g h he t h o u g h t he could fend off this particular mosasaur if need be, he didn't want to take t h e c h a n c e . But t h e marine lizard seemed u n c o n cerned with h i m , if it h a d seen h i m at all; it dashed again into the crowd of far slower a m m o n i t e s , taking t h e body c h a m b e r of o n e of t h e larger ammonite's shells in its jaws. W i t h a rending crack the shell broke, and the slashing jaws quickly tore into t h e now-exposed body portions of the amm o n i t e . He w a t c h e d t h e victim disappear in an explosion of blue blood and t h e n slide d o w n t h e gullet of t h e lizard as it turned toward a n o t h e r fleeing ammonite. He swam quickly forward and d o w n and snagged t h e largest piece of falling shell. He looked for t o o t h marks or any evidence t h a t would alert some future paleontologist to t h e true n a t u r e of the predatory attack he had just witnessed. Like t h e first bit of shell he had caught earlier in his dive, this fragment bore no holes. T h e a m m o n i t e s retreated i n t o t h e distance, still menaced by the small mosasaur, and o n c e again he was alone in t h e uppermost region of the C r e taceous o c e a n . A brisk wind had risen during his dive, and he was buffeted by t h e wave action only 10 feet above his head. He looked again at his watch and saw t h a t he was n o w free to surface. He watched small fish skim just be220

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n e a t h the wavetops and found himself trying to see t h e smaller life forms around him, wishing he had some way to look at t h e p l a n k t o n and search for the juveniles or larvas of creatures whose adult forms were familiar to h i m . He knew that tiny a m m o n i t e s , clams, snails, urchins, crabs, and at least a thousand o t h e r species surrounded h i m in these highest p o r t i o n of t h e sea, but he could see only particulate m a t t e r floating by. O u t of excuses now, and nearly out of ait, he surfaced, seeing o n c e again t h e blue-green sky, t h e scudding clouds, and the diverse and spectacular reptilian and avian pilots soaring over his head. He was well out to sea from his boat, w h i c h was just visible in t h e distance, a winking r e m i n d e r of his o t h e t life, his real life. He began to swim toward it and looked up at t h e sun. It was far lower in t h e sky a n d was descending toward t h e o c e a n to his . . . west? He stopped, pulled out his c o m pass, and laughed t h r o u g h his snorkel. A c c o r d i n g to his i n s t r u m e n t , t h e sun, now p l u m m e t i n g toward t h e horizon, was sinking i n t o t h e east. "First time a h u m a n has seen t h a t , " he t h o u g h t to himself, r e m e m b e r i n g t h a t this was a time of reversed m a g n e t i c polarity. N o r t h was s o u t h h e r e , and east was west. W h e n he finally reached t h e tethered boat, he was exhausted from the long dive and the longer swim. He released straps and slid out of his t a n k harness, free now and unfettered. After resting several minutes, just for good measure he lay prone, hyperventilated, and piked at t h e waist. He slid downward o n c e again, free-diving without a tank, t h e first marine m a m m a l in this world, and cranked off a 30-foot dive in spite of his fatigue. He got a last glimpse of the Cretaceous sea b o t t o m and was rewarded with t h e sight of a last a m m o n i t e , a heavily o r n a m e n t e d Hoplitoplacenticeras. C o m i n g up, he again passed through t h e zone of p l a n k t o n , and he paused only a meter below the surface to look more closely at the thick p l a n k t o n soup. N e a r his face mask were u n n u m b e r e d small round shells, a millimeter or two in diameter, with tiny tentacle faces e x t e n d i n g out of t h e apertures. W i t h a shock of recognition, he realized he was in a sea of newly h a t c h e d a m m o n i t e s , thousands living in t h e top few meters of t h e sea at this early stage of their lives. Lungs burning, he returned to the surface. 221

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He had only to wait now, and this journey would be over. But he looked toward t h e land and t h o u g h t about the inland sea t h a t must exist just behind those coastal m o u n t a i n s , a sea t h a t would m i m i c t h e m u c h later Sea of Cortez, w h i c h he k n e w to be filled with giant reefs of clams, n o t corals, and with a m m o n i t e s from Texas, such as t h e great snail-like Didymoceras and Nostoceras, and with t h e largest a m m o n i t e s of western N o r t h America, Pachydicus catarinae, n a m e d for a tiny fishing village in Baja California. He knew t h e future Rosario formation of Baja lay only a short distance to the east ("but west by my compass," he laughed to himself)—inland, anyway, into t h e heart of t h e N o r t h A m e r i c a n c o n t i n e n t — a n d he t h o u g h t he could get there easily and see dinosaurs to boot, realizing a final dream. But w h o would ever k n o w about these wonders? He could never return to his own time if he took t h a t voyage. He would learn m u c h , e v e n if he lived only ano t h e r day h e r e . But was it worth it to k n o w t h e answet to a question if you could n e v e r tell any o t h e r h u m a n about it? Was science simply learning the answer? Or was dissemination of t h e results a vital part as well? As he settled into t h e cockpit, he reflected on such matters and on everything he had seen during his time travels. T h e informed imagination, he decided, may be t h e best time m a c h i n e of all.

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full throttle the engine roared, a n d we skimmed over t h e glassy flat

sea. I watched the cliffs of Sucia Island fall away. T h e island's dark-shale coastline rapidly receded, c h a n g i n g from a pile of acutely visible sedimentary rock to a more ambiguous low shape. T h e boat was crowded: Tom Daniel and his family were aboard, as were my wife and new baby boy. We had just spent two wonderful days on Sucia, camping on its n o r t h e r n shore, finding fossils during t h e day, and watching the bright stars each night before retiring. Now, t h e weekend finished, we headed east toward our l a u n c h i n g site. O t h e r islands began to snake by now, smaller bits and pieces of Wrangellia. But somewhere during this hour-long voyage we crossed a great 223

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boundary, the fault marking t h e edge of Baja British C o l u m b i a . S o m e w h e t e b e n e a t h us lay t h e last a m m o n i t e fossil. S o o n a n o t h e r island began to loom large, a place called Lummi Island, composed entirely of 50-million-year-old sediments and fossils. T h e first piece of N o r t h A m e r i c a . O u r boat became t h e true time m a c h i n e , carrying us from older to younger rock, from lithic fragments of t h e A g e of Dinosaurs to equally hard but more recently formed rocks, pieces left from t h e earliest times of t h e A g e of Mammals. It carried us over large stretches of t h e planet as well: from a land t h a t o n c e sat off Mexico to a land t h a t has b e e n here, in this corner of N o r t h America, for an equally long time. It was still a beautiful day w h e n we arrived at the boat launch and readied t h e boat for its tow to Seattle, back to t h e customary routines of life. But I was already plotting. W i t h this boat I can rapidly reach every small island in t h e region or simply sit offshore of new places, new research regions. A n d w h o knows, perhaps some day this boat will indeed take me to the Mesozoic mainland, where t h e dinosaurs still roam.

::4

References

b a n n o n j , d b o t t j e r , s l u n d , a n d l s a u l . 1989. C a m p a n i a n Maastrichtian stage boundary in southern California: Resolution and implications for large-scale depositional patterns. Geology 17: 8 0 - 8 3 . BIRKELUND t, JM h a n c o c k , mb h a r t , PF r a w s o n , J r e m a n e , F robaszynski, F schmid, a n d F surlyk. 1984. C r e t a c e o u s stage boundaries—proposals. Bull Geol Soc Denmark 3 3 : 3 - 2 0 . B u r n e t t j, j H a n c o c k , w Kennedy, a n d a l o r d . 1992. Macrofossil, p l a n k t o n i c foraminiferal and nannofossil zonation at t h e C a m p a n i a n Maastrichtian boundary. Newslet Stratigraphy 7: 1 5 7 - 1 7 2 .

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b u t l e r rf, wr dickinson, a n d ge g e h r e l s . 1991. Paleomagnetism of coastal California and Baja California: A l t e r n a t i v e to large-scale northward transport. Tectonics 10 ( 5 ) : 9 7 8 - 9 8 5 . c h r i s t e n s e n wk. 1988. U p p e r Cretaceous belemnites of Europe: State of the art. In Streel, M., and M.J.M. Bless. The Chalk District of the Euregio Meuse-Rhine (pp. 1 - 1 6 ) . Selected papers on t h e U p p e r Cretaceous. Naturhistorisch Museum, Maastricht, Liege University. c o b b a n w. 1994- Diversity and distribution of late C r e t a c e o u s a m m o n i t e s in t h e W e s t e r n Interior. In Caldwell and E. Kauffman, eds. Evolution of the Western Interior Basin G e o l Assoc C a n a d a , Special Paper 39: 435-451. filmer p a n d J kirschvink. 1989. A paleomagnetic constraint on the Late C r e t a c e o u s paleoposition of n o r t h w e s t e r n Baja California, Mexico. J Geophys Res 94: 7 3 3 2 - 7 3 4 2 . fry j, d b o t t j e r , a n d s l u n d . 1985. Magnetostratigraphy of displaced upper C r e t a c e o u s strata in s o u t h e r n California. Geology 13: 6 4 8 - 6 5 1 . g a l e a, p m o n t g o m e r y , w kennedy, j h a n c o c k , j b u r n e t t , a n d j m c a r t h u r . 1995. Definition and global correlation of t h e S a n t o n i a n - C a m p a n i a n boundary. Terra Nova 7: 6 1 1 2 - 6 2 2 . g r a d s t e i n f, et a l . 1994. A Mesozoic time scale. ] Geo Res 99: 24,051 - 2 4 , 0 7 4 h a g g a r t j . 1990. N e w and revised a m m o n i t e s from t h e upper Cretaceous N a n a i m o G r o u p of British C o l u m b i a and W a s h i n g t o n State. Geo! Surv C a n a d a Bull 396: 1 8 1 - 2 2 1 . h a g g a r t j , a n d p w a r d . 1984. Late C r e t a c e o u s stratigraphy o f the n o r t h e r n S a c r a m e n t o Valley, California. G S A Bull, 9 5 : 6 1 8 - 6 2 7 . h a n c o c k j, a n d a g a l e . 1996. T h e C a m p a n i a n Stage. Bull Inst Roy Sci Nat Befe 66: 1 0 3 - 1 1 0 .

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h a n c o c k J, a n d w Kennedy. 1993. T h e high Cretaceous a m m o n i t e fauna from Tetcis, Landes, France. Bull Inst Roy Sci N a t Be!g63: 1 4 9 - 2 0 9 . . 1988. Mesozoic and Cenozoic chronostratigraphy a n d cycles of sea level change. Society of Economic Paleontologists and Mineralogists Special Publication 42: 7 3 - 1 0 8 . h a n c o c k J, n peake, J b u r n e t t , a d h o n d t , w kennedy, a n d r s t o k e s . H i g h C r e taceous stratigraphy at Tercis. Bull Inst Roy N a t Bel 6 3 : 1 3 3 - 1 4 8 . h a q b, j h a r d e n b o l , a n d p vail. 1987. T h e chronology of fluctuating sea levels since t h e Triassic. Science 235: 1 1 5 6 - 1 1 6 6 . h a r d e n b o l J, J t h i e r r y , m farley, t j a c q u i n , p de g r a c i a n s k y , a n d p v a i l . C r e taceous chronostratigraphy. In P. De Graciansky, ed. Sequence Stratigraphy in European Basins. S E P M Special Publication. In press. hicks J. 1993. C h r o n o s t r a t i g t a p h i c analysis of t h e foreland basin sediments of the latest Cretaceous, W y o m i n g , U S A . Yale University doctoral thesis. h o w e l l d. 1993. Principles of Terrane Analysis. L o n d o n : C h a p m a n and Hall. kauffman e, a n d r kesling. 1960. An U p p e r Cretaceous a m m o n i t e b i t t e n by a mosasaur. University of Michigan Museum Paleontology Contribution 15: 193-248. Kennedy wj. 1986. C a m p a n i a n and M a a s t r i c h t i a n a m m o n i t e s from n o r t h e r n A q u i t a i n e , France. Palaeontological Association of London. Special Papers in Palaeontology, 36: 145. . 1989. T h o u g h t s on t h e evolution and e x t i n c t i o n of C r e t a c e o u s ammonites. Proceedings of the Geologists Association 100: 2 5 1 - 2 7 9 . l i l l e g r a v e n J. 1991. Stratigraphic p l a c e m e n t of t h e S a n t o n i a n - C a m p a n i a n boundary in the N o r t h A m e r i c a Gulf Coastal Plain and W e s t e r n Interior. Cret Res 12: 1 1 5 - 1 3 6 . m a c l e o d n, et a l . 1997. T h e Cretaceous-Tertiary biotic transition. ) Geol Soc London 153: 2 6 5 - 2 9 2 .

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m a r k s p. 1984- Proposal for t h e recognition of boundaries between Cretaceous stages by means of p l a n k t o n i c foraminiferal biostratigraphy. Bull Geol Soc Denmark 3 3 : 1 6 3 - 1 6 9 . m c a r t h u r J, w kennedy, m c h e n , m TH1RLWALL, a n d a g a l e . 1994- S t r o n t i u m isotope stratigraphy for Late Cretaceous time: Direct numerical calibration of t h e Sr isotope curve based on t h e U . S . Western Interior. Paleo Paleo Paleo 108: 9 5 - 1 1 9 . n e l s o n b, k m a c l e o d , a n d p w a r d . 1991. Rapid c h a n g e in strontium isotopic composition of sea water before t h e Cretaceous/Tertiary boundary. N a ture 3 5 1 , 6 4 4 - 6 4 7 . o b r a d o v i c h J. 1993. A C r e t a c e o u s time scale. In Caldwell and E. Kauffman, eds. Evolution of the Western Interior Basin. Geol Assoc C a n a d a , Special Paper 39: 3 7 9 - 3 9 6 . p e s s a g n o e. 1967. U p p e r Cretaceous p l a n k t o n i c foraminifera from the western gulf coastal plain. Paleontological Americana, 5: 2 4 3 - 4 4 2 . premoli-silva i a n d w s l i t e r . 1994- Cretaceous foraminiferal biostratigraphy and evolutionary trends from t h e Bottaccione section, G u b b i o , Italy. Pal l t d 82: 1 - 8 9 . s a u l l. 1988. N e w Late C r e t a c e o u s a n d early Tertiary Perissityidae (Gastropoda) from the Pacific Slope of N o r t h A m e t i c a . Cont Sc, LA County Museum, 400: 25. s l i t e r w. 1968. U p p e r C r e t a c e o u s foraminifera from southern California and n o r t h w e s t e r n Baja California, Mexico. University of Kansas Paleontological Cont. 49, 141. . 1984- C r e t a c e o u s foraminiferans from La Jolla, California. In P A b b o t , ed. Upper Cretaceous Depositional Systems, Southern California, Northern Baja California. S E P M book 49, 1 7 - 2 4 s u g a r m a n p, k miller, d bukry, a n d m feigenson. 1995. U p p e r m o s t C a m p a n ian Maastrichtian s t r o n t i u m isotope biostratigraphic and sequence

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sttatigraphic framework of N e w Jersey coastal plain. G S A Bull. 107: 19-37. t o s h i m i t s u s, t m a t s u m o t o , m n o d a , t nishida, a n d s maiya. 1995. Toward an integrated mega-, micro- a n d magnetostratigraphy of t h e U p p e r Cretaceous in Japan. j Geol Soc Japan 101: 1 9 - 2 9 . v e r o s u b K, j h a g g a r t , a n d p w a r d . 1989. Magnetostratigraphy of U p p e r C r e taceous strata of t h e S a c r a m e n t o Valley. California Bull Geol Soc Am 101: 5 2 1 - 5 3 3 . w a r d , p. 1978a. Revisions to t h e stratigraphy and biochronology of t h e U p p e r Cretaceous N a n a i m o G r o u p , British C o l u m b i a and W a s h i n g t o n State. C a n J Earth Sciences 15: 4 0 5 - 4 2 3 . w a r d p. 1978b. Baculitids from t h e N a n a i m o G r o u p , Vancouver Island and W a s h i n g t o n S t a t e . J Paleontol 52: 1143 - 1 1 5 4 . w a r d p, a n d j h a g g a r t . 1981. T h e U p p e r Cretaceous a m m o n i t e and inoceramid bivalve succession at S a n d C r e e k , Colusa C o u n t y , California, and its implications for establishment of an U p p e r C r e t a c e o u s G r e a t Valley Sequence a m m o n i t e zonation. Newslet Stratigraphy, 10, 1 4 0 - 1 4 7 . w a r d pd, a n d wj Kennedy. 1993. Maastrichtian a m m o n i t e s from t h e Biscay region (France and S p a i n ) . J Paleontol, M e m o i r 34w a r d p, K v e r o s u b , a n d j h a g g a r t . 1983. M a r i n e magnetic anomaly 3 3 - 3 4 identified in t h e U p p e t C t e t a c e o u s of t h e G r e a t Valley S e q u e n c e of California. Geology 11: 9 0 - 9 3 .

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Index

Absolute temperature scale, 36

best-preserved, 42

Accretion tectonics, 84

Cretaceous, 18, 24

Age of Dinosaurs, 128-129

evolution of, 4 2 - 4 3

Allonautilus genus, 185-186

in Haslam Formation, 113-114

evolutionary history of, 188

from Hornby Island, 74

Alvarez, Walter, 54-56, 65

in Late Cretaceous Period, 3 3 - 3 4

Ambiguity, ix

Mesozoic, 213, 217-221

Ammonite, 42

mosasaurs "eating," 135-146

Ammonite septa, 155

planispiral, 219

Ammonite sutures, 151 - 1 6 0

species of, 15

Ammonites, xv, 11, 23, 102, 112,

Tunisian, 122-123

171-172

uncoiled, 128

Baculites, 30-32

virtual, 147-168 231

T I M E

M A E H I N E 5

Ancient environments, sea level

Bridgewater Treatise (Buckland), 157

change and, 113-119

British Columbia, Baja, 73-104

Ancient giant clams, 192-195

Brunhes Normal Epoch, 51

Ancient predation, evidence of, 130-135

Buckland, Dean, 156-157

Anston, F. W., 40

Burgess Shale creatures, 150

Apatite, 148 Appalachian Mountains, 83

California, 8 9 - 9 1

Argon, 39

Baja, 7 7 , 9 9 - 1 0 2

Ash, volcanic, 42

Cambrian Period, 17

Asia and India, collision of, 82

Cambrian System, 17

Asteroid, 56

Campanian Stage, 21

Athenaeum faculty club, 99

Canada

Atomic weight, 39

Geological Survey of, 29

Australia, Indonesia and, 85

Western, morphogeological belts of, 92

Autotrophs, 195-196

Canadian fossils, 30 Canadian Gulf Islands, 191-192 Carbon-14, 39

Baculites fossils, 3 0 - 3 2 Baculites inomatus, 69

Cascade volcanoes, 89

Baja British Columbia, 73-104

Catastrophes, global, 17

Baja British Columbia hypothesis, 97

Catastrophic global climate change, 120

Baja California, 77, 99-102

Catastrophism, 21

Bakker, Bob, 140-142

Cenoceras, 182, 186

Barnes Island, 28

Cenozoic Era, 11,17

Basalt, Mesozoic-aged, 80

Cephalopods, 149

Bay of Fundy, 115

fossil, 156

Beard, Graham, 129

Chain saw as coring device, 57, 59

Beck, Merle, 91,98

Chambered nautilus, 173

Becquerel, A., 38

Chemoautotrophic bacteria, 202

Bentonite, 41

Chico Creek, 6 0 - 6 4

Biological structures, 148

Chicxulub comet impact, 74, 122, 172

Biomass, 196

Chromatophores, 218

Biostratigraphy, 2 8 - 3 2

Cladistics, 179

Bipolar magnets, 47

Clams

Bosvrychoceras polyplocum ammonite, 123

Cretaceous, 212-213

Bottjer, David, 64

giant, 33

Brandon, Mark, 97

ancient, 192-195

Breaks in fossil shells, 130

inoceramids, xv, 112, 193-204 232

I n d e x

Clamshells, 8

Cretaceous/Tertiary boundary, see "K/T

Classification of life, 170-175

boundary

Climate change, catastrophic

Cretaceous time, 43

global, 120

Cross beds, 110

Clocks

Curie, Marie, 38

magnetic, 4 5 - 6 9

Curie point, 63

radiometric, 3 3 - 4 3 Cobbles, 109

Daniel, Sophie, 141

Coelacanth, 181

Daniel, Tom, 141-144,

Cold methane seeps, 201-204

162-168, 223

Comet impact, Chicxulub, 74, 122, 172

Darwin, Charles, 35, 36, 171

Communities, 195

Data, interpretation of, x

hydrothermal vent, 200-202

Dating

Compaction shallowing, 104

magnetostratigraphic, 55

Composite material, 143

radiometric, 35

Concrete, 143

Decay, radioactive, 3 8 - 4 1

Concretions, xiv-xv

Declination of earth's magnetic

Conglomerates, 109-110

field, 48

Coniacian Stage, 19, 21

Deep sea cores, 54

Contact, zonal, 26

Deep Sea Drilling Program, 57

Continental drift, 73, 7 6 - 8 9

Denton, Eric, 160

Continental glaciation, 116

Derived characters, 179

Convection cells, 81

Deserrs, 106

lithic, 78

Devonian Period, 161-162

Coring device, chain saw as, 57, 59

D'Halloy, D'Omalius, 19

Courtney museum, 128

Dinofest2, 140-142

Cowan, Darrel, 97

Dinosaurs, xv

Craton, travel paths of Western North

Age of, 128-129

America relative to, 93

Direction

Cretaceous ammonites, 18, 24

paleomagnetic, 50

Cretaceous clams, 212-213

sense of, 100

Cretaceous Period

DNA, 170

dates of, 61

D'Orbigny, Alcide, 19, 21, 25, 27, 28,

end of, x

43, 54, 156

Cretaceous stages, magnetochrono-

Downey, Roger, 128

stratigraphy and, 68

Du Toit, Alexander, 78, 7 9 - 8 0

Cretaceous System, 17, 19, 25

Dzik.J., 178 233

T I M E

M A C H I N E S

Earth

Fossils, xv, 7, 146

age of, 5, 3 4 - 4 1

Baculites,

30-32

earthquake waves through, 50

Canadian, 30

iron core of, 48

law of superposition of, 12

as magnet, 4 7 - 4 8

living, 175-178

magnetic field of, 48

from measured sections, 13

onion analogy for, 81

as relative indicators of time, 16

Earthquake waves through earth, 50

in sedimentary rocks, 32

Ebb tides, 115

Functional morphology, 147, 150

El Kef, Tunisia, 121-122 Elasmosaur, 1 2 8 - 1 2^)

Gabb, William, 2 2 - 2 3 , 25, 27, 32, 56,

Environments, ancient, sea level

60-61

change and, 113-119

Gabriola Island, 192-193

Eocene-aged rocks, 96

Garver, John, 97

Eustatic sea level change, 117

Gauss Normal Epoch, 51

Evolution, 148-149

Gel electrophoretics, 184 Genetic drift, 189

theory of, 35, 36 Extension Formation, 115

Geological maps, 16

Extinction controversy, 56

Geological Survey of Canada, 29

Extinctions, mass, 17, 56, 106, 119

Geological time scale, 5

Faculty clubs, 99

Geology, 4, 86, 87

FEA (finite element analysis), 164

Geomagnetic polarity time scale

historical development of, 20

Feldspar, 42

(GPTS), 4 6 - 5 3

Finite element analysis (FEA), 164

Geomagnetic poles, 80

Flood tides, 115

Geophysics, 8 6 - 8 7

Flower, Rousseau, 156

Georgia Strait, 127

Food chains, 195

Giant clams, ancient, 192-195

Foraminiferans, 25, 199

Gilbert Reversed Epoch, 51 Gills, 148

planktonic, 55 Fossil Bay, xiii, xv

Gilpin-Brown, John, 160

Fossil Beach, 75, 129

Glacial tillites, 80

Fossil-bearing rocks, viii

Glaciation, continental, 116

Fossil cephalopods, 156

Global catastrophes, 17

Fossil prizes, 14

Global climate change, catastrophic, 120

Fossil shells, breaks in, 130

Gold Rush, 60

Fossiliferous outcrops, xiv

Gondwana Sequence, 80

234

I n d e x

Gondwana succession, 7 8 - 7 9

Implosion, 152, 153

(iondwanaland, 79-80

Inclination of earth's magnetic field, 48

Gould, Stephen Jay, 7, 150, 159, 187

Inclination shallowing, 104

GPTS (geomagnetic polarity time

India and Asia, collision of, 82

scale), 4 6 - 5 3

Indonesia, Australia and, 85

Granite, 34

Inoceramids, xv, 112, 193-204

Gulf Islands, 113

Insular Superterrane, 97 Intensity of earth's magnetic field, 48

1 laggart, Jim, 45, 64

Intermontane region, 97

Half-life, 39

Interpretation of data, x

Hardness of rocks, 6

Intertidal zonations, 10

Haslam Formation, 113-114

Iridium, 56

ammonites in, 113-114

Iron core of earth, 48

hleat flow, 36

Irving, Ted, 9 6 - 9 8

Hell's Canyon, 96

Isotopes, 34, 39, 198

Helmuth, Brian, 165

Isotopic pairs, 39

Hewitt, Roger, 161

Isotopic ratios, oxygen, 198-200

High stands, 118 Himalayas, 82

Jeletzky, George, 2 9 - 3 2

Historical development of geological

Johnson, Paul, 139

time scale, 20

Jurassic Park, 150

Hooke, Robert, 154-156 Hoplitoplacenticeras, 69

K/Ar (potassium/argon) method, 3 9 - 4 0

Hoppe, Kathryn, 200

"K/T" boundary (Cretaceous/Tertiary

Hornby Island, xvi, 7 4 - 7 6

boundary), 17,66, 119, 121

ammonites from, 74

mass extinction at, 17, 56, 106, 119

Horner, Jack, 140

Kase, Tatsuro, 139

Hurtado, Jose, 102, 103

Kauffman, Erie, 135-138, 140-143, 145

Huxley, Thomas, 37

Kelvin, Lord (William Thomson),

Hydrostatic pressure, 153

3 5 - 3 9 , 87

Hydrothermal vent communities,

Kennedy, W. James, 156

200-202

Kesling, A., 135-138 King, Clarence, 37

Ice Ages, 8, 116

Kirschvink, Joseph, 9 9 - 1 0 4

Ichthyosaurs, 131, 132

Komodo dragon, 130-131, 220

Igneous rocks, 41

Kullman, Jurgen, 159

Iguanas, marine, 133

Kummel, Bernard, 177-178

235

T I M E

M A C H I N E S

Landman, Neil, 186

Magnetometers, 58, 63, 103

Larson, Neil, 142

Magnetostratigraphic dating, 55

Late Cretaceous Period, North America

Magnetostratigraphy, 69

in, 3 3 - 3 4

Magnetozone 33R, 69

Late Cretaceous Stage, 21

Mantle, 81

Lehmann, Ulrich, 156

Maples, Chris, 166

Life

Mapping of North America, 22

classification of, 170-175

Maps, geological, 16

sea level change and, 119-121

Marine iguanas, 133

Limestone, 16

Martin, Arthur, 138

shallow-water, 54

Mass extinctions, 17, 56, 106, 119

Limestone bodies, 202

Mass spectroscopes, 4 0 - 4 1

Limpets, 134, 139, 146

Matsumoto, Tatsuro, 31, 178

Lithic convection cells, 78

Matuyama Reversed Epoch, 51

Lithification, 8

McPhee, John, 84

Living fossils, 175-178

Measured sections, fossils from, 13

Low stands, 118

Memories, ix

Lowrie, William, 5 4 - 5 5 , 65

Mesozoic-aged basalt, 80

Lummi Island, 224

Mesozoic ammonites, 213, 217-221

Lyons, Jerry, x

Mesozoic Era, viii, 8 - 9 , 11, 17 Sucia Island in, science fiction of,

MacLeod, Ken, 200

208-222

Magma, 34

Methane seeps, cold, 201-204

Magnet(s)

Meyerhoff, Al, 77

bipolar, 47

Microfossils, 55

earth as, 4 7 - 4 8

Microplates, 8 4 - 8 5

Magnetic anomalies, formation of, 51

Mid-ocean ridge spreading center, 51

Magnetic clocks, 4 5 - 6 9

Miller, A. K., 176-178, 187

Magnetic field of earth, 48

Mineral grains, magnetic resetting

Magnetic pole(s)

of, 88

modem north, 49

Mining, 5 - 6

secular movement of, 48

Modern north magnetic pole, 49

Magnetic resetting of mineral grains, 88

Molluscan shells, 143

Magnetism, rock, 8 7 - 8 8

Monitor lizards, 131

Magnetite, 53

Morphogeological belts of Western

Magnetochronostratigraphy, Cretaceous stages and, 68

Canada, 92 Morphology, functional, 147, 150

236

I n d e x

Mosasaurs, xvi, 129, 131-147,

North America

219-220

growth of, 83

"eating" ammonites, 135-146

in Late Cretaceous Period, 3 3 - 3 4

Mount, Jeff, 6 5 - 6 6

mapping of, 22

Mt. Baker, 91

Western, see Western North

Mt. Stuart, 9 1 - 9 4 , 98

America

Mountains

North magnetic pole, modern, 49

complexity of, 84

Nuclear submarine Thresher, 152

formation of, 82 primitive, 6

Ocean basins, 54, 7 7 - 7 8

secondary, 6

Ocean Drilling Program, 54

Mudstones, 74

Oceanic crust, 52

Museums, 28

Oceans, temperature of, 198-204

natural history, 2 8 - 2 9

Octopuses, 149 Offlap, 118

Nanaimo Group, xvii, 98, 113

Onion analogy for earth, 81

Nanaimo Group strata, locations

Onlap, 118

of, xviii

Oppel, Albert, 158

Natural history museums, 2 8 - 2 9

Orcas Island, xii-xiii, 7, 12, 28

Naturalists, 35

Oxygen isotopic ratios, 198-200

Nautiloids, fossil, xv Nautilus, 138, 167, 171

Pacific Plate, descending, 85

ancestry of, 169-189

Paleoecology, 196

chambered, 173

Paleomagnetic direction, 50

classifying, 180-185

Paleomagnetic time machine, 65

pearly, 214-215

Paleomagnetics, 62, 8 6 - 8 8

Nautilus Nautilus

belauensis,

180,

Paleomagnetism, 4 6 - 5 2 , 75

184

genus, 174

terrane analysis using, 91

evolutionary history of, 188 Nautilus

macromphalus,

Nautilus pompilius, Nautilus

180,

184,

Paleontology, viii Paleozoic Era, 17

189

180, 182-184, 189

scrobiculatus,

start of, 16

180-185

Past, ix

Nautilus shells, 141 Nautilus Neopilina,

stenomphalus,

Pearly nautiluses, 214-215 180,

Permian Period, 162

184

Permian System, 17

181

New Caledonian barrier reefs, 176

Perpetual motion machines, 36

Newton, Isaac, 154

Pfaff, A., 158

237

T I M E

M A C H I N E S

Phenetics, 178-179

Reversals of polarity, 4 8 - 5 2

Phillips, John, 17

Rifting process, 86

Phylogenetic systematics, 174

Rock magnetism, 8 7 - 8 8

Physicists, 208

Rocks, viii, xi

Pinna

clam, 111

Placenticeras

ammonites,

age of, 3-7 139

Eocene-aged, 96

Planispiral ammonites, 219

fossil-bearing, viii

Plankton, 197

hardness of, 6

Planktonic foraminiferans, 55

igneous, 41

Plate tectonic theory, 52

reheated, 63, 98

Plate tectonics, 7 6 - 8 9

sedimentary, see Sedimentary rocks

Plates, 8 1 - 8 2

Vancouver Island, 101

Plesiosaurs, xvi, 131, 132

volume of, within spreading cen-

Polarity, reversals of, 4 8 - 5 2

ters, 117

Polarity Epochs, 51

Rocky Mountains, 34

Polarity time scale, 52

Roentgen, Wilhelm, 38

Poles, geomagnetic, 80

Roux, Erica, 143-144

Potassium/argon (K/Ar) method,

Royal Tyrell Museum, 138-139

39-40

Rutherford, Ernest, 38

Predation, ancient, evidence of, 130-135

Salt clock, 37

Primitive mountains, 6

San Andreas fault, 8 2 - 8 3

Pterosaurs, 210

San Francisco, 89

Puget Sound, xix, 10

San Juan Island, xii, 10

Puntledge River, 128-129

Sandstone, 110-111 Saunders, Bruce, 161, 165, 180-186

Queen Charlotte Islands, 97

Scallops, 10

Quendstedt, Albert, 158

Schindewolf, Otto, 159 Science fiction of Sucia Island in Mesozoic Era, 208-222

Radioactive decay, 3 8 - 4 1 Radioactivity, 34, 3 8 - 3 9

Science magazine, 103

Radiometric clocks, 3 3 - 4 3

Scientific method, vii

Radiometric dating, 35

Sea level, 115

References, 225-229

Sea level change, 105-106, 116-118

Regression, 118

ancient environments and, 113-119

Reheated rocks, 63, 98

eustatic, 117

Relative time, 4

life and, 119-121

238

I n d e x

Sea level curve, worldwide, 124

South Africa, 79

Sea shells, 130

Spreading centers, 52, 80

Sea turtles, 138

mid-ocean ridge, 51

Seattle, 99

volume of rock within, 117

Second law of thermodynamics, 36

Squires, Richard, 186-187

Secondary mountains, 6

Stages as units of time, 19, 21

Secular movement of magnetic

Stratigraphy, 9, 1 1 - 1 2 , 7 8

poles, 48

seismic, 118

Sedgewick, Adam, 16-17

Stratotypes, 64

Sedimentary heds, 9

Strike slip motion, 89

Sedimentary rocks, viii, 105-111

Subduction zones, 78, 81

accumulation of, 106

Submersibles, 152

fossils in, 32

Sucia Island, x, xii-xix, 7, 98

of Sucia Island, 107-112

age of, 3 - 7

thickness of, 37

in Mesozoic Era, science fiction of,

Sedimentary structures, 106

208-222

Sedimentology, 106

sedimentary rocks of, 107-112

Seilacher, Dolph, 159

site of, xv-xix

Seismic stratigraphy, 118

stratigraphic location of, 2 5 - 2 8

Sense of direction, 100

telephone book analogy of, 107-109

Septa

voyage to, xii-xiii

ammonite, 155

winter trip to, 12-14 Suess, Eduard, 79

internal, 154

Superposition of fossils, law of, 12

Shale, 114

Suspect terrane, 73, 8 4 - 8 6

Nanaimo Group, xvii Shallow-water limestone, 54

Sutures, ammonite, 151-160

Shimansky, V., 178

Systematics, 170

Sierra Nevada Mountains, 23

phylogenetic, 174

Silicon Graphics workstations, Taxon/taxa, 14, 178

163-164 Simpson, George Gaylord, 159

Taxonomy, 170

Skagit Valley, xii

Tectonics, accretion, 84

Smit, Jan, 67

Teichert, C, 178

Smith, William, 15-16, 19, 23, 26,

Telephone book analogy of Sucia Island, 107-109

28, 156 Soddy, Frederick, 38

Temperature of oceans, 198-204

Sollas, William, 37

Temperature scale, absolute, 36

239

T I M E

M A C H I N E S

Time scale

Terrane, 86 suspect, 73, 8 4 - 8 6

geological, see Geological time scale

Wrangellia, 9 4 - 9 7

geomagnetic polarity (GPTS), 46-53

Terrane analysis using paleomagne-

polarity, 52

tism, 91 Tertiary mountains, 6

Transgression, 118

Tessier, Robert, 91

Trask, Mike, 128-129

Texada Island, 102-103

Trigonia

Thermodynamics, second law of, 36

Trigoniids, xv

Thompson, J. J., 40

Trophic group analysis, 195-197

Thomson, William (Lord Kelvin),

Tunisia, 120-124

clam, 111

Tunisian ammonites, 122-123

35-39,87

Tunnicliffe, Verena, 203-204

Thought experiments, 208 Thresher nuclear submarine, 152 Tides, 115

Umhoefer, Paul, 97

Tillites, glacial, 80

Underwater volcanoes, 52

Tilting, 94

Uniformitarianism, 106

Time

principle of, 11

Cretaceous, 43

Urey, Harold, 198

fossils as relative indicators of, 16

Van Andel, Tjeerd, 200-201

relative, 4

Vancouver Island, xvi, 23, 127

standard for, 43

Vancouver Island region, 73 Vancouver Island rocks, 101

Time-keeping, 4 - 5 The Time Machine

(Wells),

Vent fauna, 201

x

Verosub, Ken, 57, 59, 62, 76

Time machines, vii detailed observations as, 124

Virtual ammonites, 147-168

devices as, ix

Vital effects, 200

functional morphology as, 147

Volcanic ash, 42

informed imagination as, 222

Volcanoes, 34

microcomputers as, 168

Cascade, 89

natural history museums as, 29

underwater, 52

one of first, 16 paleomagnetic, 65

Wainright, Steven, 149, 162

radiometric methodology as, 34

Waldron Island, 27

from science, xvii-xviii

Wegener, Alfred, 78, 79-80

scientific method as, 146

Wells, H. G., x

240

I n d e x

Wells, Martin, 149

Willey, Arthur, 181, 182

Westermann, Gerd E. G., 153,

Woodruff, David, 184

159-161, 166

Worldwide sea level curve, 1

Western Canada, morphogeological

Wrangellia terrane, 9 4 - 9 7

belts of, 92

Wray, Charles, 184

Western Interior Seaway, 33, 42, 135 Western North America, 90

Zonal contact, 26

travel paths of, 93

Zonations, intertidal, 10

Wiedmann, Jost, 159, 178

Zumaya, Spain, 6 5 - 6 7

241

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Time and Time Again

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