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<p>The Emerald Planet</p> <p>This page intentionally left blank</p> <p>This page intentionally left blank</p> <p>The Emerald PlanetHow plants changed Earths historyDavid Beerling</p> <p>1</p> <p>Great Clarendon Street, Oxford ox2 6dp Oxford University Press is a department of the University of Oxford. It furthers the Universitys objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With oYces in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries Published in the United States by Oxford University Press Inc., New York David Beerling 2007 The moral rights of the author have been asserted Database right Oxford University Press (maker) First published 2007 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this book in any other binding or cover and you must impose the same condition on any acquirer British Library Cataloguing in Publication Data Data available Library of Congress Cataloging in Publication Data Data available Typeset by SPI Publisher Services, Pondicherry, India Printed in Great Britain on acid-free paper by Clays Ltd, St Ives plc ISBN 9780192806024 10 9 8 7 6 5 4 3 2 1</p> <p>3</p> <p>For Juliette</p> <p>Preface</p> <p>The great evolutionary biologist J.B.S. Haldane (18921964), on being asked by a cleric what biology could say about the Creator, entertainingly replied, Im really not sure, except that the Creator, if he exists, must have an inordinate fondness of beetles. Haldane was referring to the fact that approximately 400 000 species of beetles make up roughly 25% of all known animal species. Current estimates for the total number of species of Xowering plants in the world (300 000400 000), had they been available to him at the time, may have given Haldane pause for thought about his riposte. Plants and beetles may be tied, stem and thorax, in the global biodiversity stakes but when it comes to capturing our own fascination, plants are way ahead, clear winners in the popularity stakes. We have been collecting, classifying, and cultivating Xoras worldwide for centuries. Not only do plants provide us with fuel, food, shelter, and medicines that sustain the human way of life, but they also uplift and inspire us. Irrespective of the season, we Xock to Wne gardens, elegantly sculpted landscapes, botanical gardens, and arboretums to pay homage to the plants and trees. But how many of us have stopped to wonder how remarkable plants are, how profoundly they have altered the history of life on Earth, and how critically they are involved in shaping its climate? Only now are we unlocking vital information about the history of the planet trapped within fossil plants. My aim in writing this book has been to provide a glimpse of these exciting new discoveries because they oVer us a new way of looking and thinking about plant life. It recognizesindeed emphasizesthat plants are an active component of our planet, Earth. At the global scale, forests and grasslands regulate the cycling of carbon dioxide and water, inXuence the rate at which rocks erode, adjust the chemical composition of the atmosphere, and aVect how the landscape absorbs or reXects sunlight. In vi</p> <p>Pr ef a ce this book, I reveal how plant activities like these have added up over the immensity of geological time to change the course of Earth history. Never mind the dinosaurs, here is a revisionist take on Earth history that puts plants centre stage. My hope is that the book will further stimulate readers natural fascination with plantsboth the living and the long deadby revealing their activities in this new light. Each chapter leads the reader through a scientiWc detective story describing a puzzle from Earth history in which plants have played a starring role. Occasional linkages with themes from other chapters are pointed out as they arise. This format allows individual chapters to stand alone or be read in sequence. I provide a short summary at the start of each chapter to help readers quickly grasp the nature of the puzzle and glimpse the scientiWc excitement ahead. In writing a popular science book like this, it is true that, in Mark Twains words, I have got wholesale returns of conjecture out of . . . a triXing investment in fact. All sources of the facts taken from the published scientiWc literature are given in the notes, and where my ideas and conjecture are more speculative, I hope I have clearly signposted them as such. I have made every eVort to keep the text free of scientiWc jargon, but admit that the odd word or term has proved indispensable. These are deWned or explained where they occasionally crop up.</p> <p>He had been eight years upon a project for extracting sunbeams out of cucumbers, which were to be put into vials hermetically sealed, and let out to warm the air in raw inclement summers.</p> <p>Jonathan Swift (1726), Gullivers travels Humankind continues to take liberties with our planet, although not of course in the gentle manner Jonathan Swift described in Gullivers travels. By consuming fossil fuels and destroying tropical rainforests, we are undertaking a global uncontrolled experiment guaranteed to alter the climate for future generations. Plants and vegetation are major actors in the environmental drama of global warming now as they have been in the recent and more distant past. This book focuses on the distant past, Earth history from millions of years ago. As we shall see, vii</p> <p>Pr e f a c e though, this investigation of the past has much to teach us about our present predicament. It oVers us cautionary lessons about the current mismanagement of our planets resources we would be wise to heed. July 2006, SheVield D.B.</p> <p>viii</p> <p>Acknowledgements</p> <p>This book had its genesis in discussions with colleagues over a beer in a sushi bar in San Francisco, in December 2002. San Francisco is home of the fall meeting of the American Geophysical Union, an annual gathering of several thousand scientists from a host of disciplines congregate for a science feast. At the 2002 meeting, I had the prospect of delivering a belated inaugural lecture the following spring hanging over me, and was searching for an eVective way to present some of the Wndings of my research group over the past decade in an engaging way to a lay audience. One idea was to present them as a series of short stories, each beginning with a seemingly straightforward question, an approach used to good eVect by Paul Colinvaux in his admirable 1980 book Why big Werce animals are rare (Penguin, London). The basic concept of individual stories, each with plants playing the starring role, worked well on the night, and I subsequently adopted tha format here, although in all but one case the inclusion of a questionin-the-title has been abandoned. Many people have been instrumental in helping putting this book together. I extend warm thanks to Bill Chaloner (University of London) and Colin Osborne (University of SheYeld) for patiently and critically reviewing earlier drafts of the text. Many other colleagues also kindly gave of their time to critically read and comment on various chapters, provide data, ideas, and images, and engage in detailed discussions about the diVerent scientiWc issues and queries raised during the writing process. I have beneWted greatly from their input and special thanks must go to Paul Kenrick (Natural History Museum, London), Karl Niklas (Cornell University), Charles Wellman, Doug Ibrahim, Barry Lomax, Peter Mitchell, Andrew Fleming, and Ian Woodward (University of SheYeld), Robert Berner (Yale University), Jon Harrison (Arizona State University), Robert Dudley (University of California, Berkeley), Don CanWeld (Odense ix</p> <p>Ac k n o w l ed g em e n t s University, Denmark), Henk Visscher (Utrecht University), Dana Royer (Wesleyan University), Charles Cockell (Open University), Kevin Newsham and Jonathan Shanklin (British Antarctic Survey), Virginia Walbot (Stanford University), Sheila McCormick (University of California, Berkeley), Lee Kump (Pennsylvania State University), Michael Benton and Paul Valdes (University of Bristol), John Pyle and Michael Harfoot (University of Cambridge), Tim Lenton (University of East Anglia), Paul Wignall, Jane Francis and Jon Lloyd (Leeds University), Gavin Schmidt (NASA/Goddard Institute for Space Studies, New York), Barry Osmond (Australian National University) and Govindjee (University of Illinois). The corrective feedback of all of these individuals trapped numerous errors of interpretation, and crucial omissions. Any remaining errors and over-enthusiastic interpretations of datasets and published papers remain my own responsibility. The groundwork for my thinking about plants as a geological force of nature was laid in large part during my tenure of a Royal Society University Research Fellowship held between 1994 and 2001. I am extremely grateful to the Royal Society for funding my research through this mechanism. These fellowships continue to oVer unsurpassed opportunities to young scientists by giving them the most valuable commodity in their armourytime to think, free from the usual burdens of administration and teaching that normally accompany academic life. I am also grateful to the Leverhulme Trust and the Natural Environment Research Council, UK for their Wnancial support of my research. Popular science writing requires a step change in style from the more turgid prose used in writing scientiWc papers. Francis Crick (19162004), the British molecular biologist and co-discoverer of the structure of DNA, commented in his 1990 book What mad pursuit: a personal view of scientiWc discovery (Penguin, London) that there is no form of prose more diYcult to understand and more tedious to read than the average scientiWc paper. I am extremely grateful to my editor, Latha Menon, for her wise counsel and suggestions on earlier drafts that have eased the transition, and which have been instrumental in shaping the current direction of the book. Whether I have been successful in this endeavour or not is another matter; any failings remain my own. I also thank the production team at Oxford University Press for eYciently shepherding me through the x</p> <p>Ac k n o w l ed g em e n t s production process, especially Michael Tiernan the copy-editor and Sandra Assersohn for eYciently sourcing some delightful images. Finally I thank my partner Juliette for her forbearance far above and beyond the call of duty. The time that writing this book has stolen from us over the past three years astonished me as well.</p> <p>xi</p> <p>This page intentionally left blank</p> <p>Contents</p> <p>Preface vi Acknowledgements ix Illustrations and plates xiv Chapter 1 2 3 4 5 6 7 8 9 Notes 217 Index 277 Introduction 1 Leaves, genes, and greenhouse gases 9 Oxygen and the lost world of giants 35 An ancient ozone catastrophe? 61 Global warming ushers in the dinosaur era 87 The Xourishing forests of Antarctica 115 Paradise lost 143 Natures green revolution 171 Through a glass darkly 197</p> <p>xiii</p> <p>Illustrations and plates</p> <p>Fig. 1 How the geological timescale relates to the chapters in the book. Fig. 2 The enigmatic early Devonian vascular plant Eophyllophyton bellum. (From Hao, S.G. and Beck, C.B. (1993) Further observations on Eophyllophyton bellum from the lower Devonian (Siegenian) of Yunnan, China. Palaeontographica, B230, 2747. Reproduced with permission.) Fig. 3 Changes in the Earths atmospheric oxygen content and giant insect abundance over the past 540 million years. Fig. 4 The development of the ozone hole above Antarctica. (Data courtesy of J.D. Shanklin, British Antarctic Survey.) Fig. 5 Fossil evidence for a global mutagenesis event? (From Looy, C.V., Collinson, M.E., Van Konijnenburg-Van Cittert et al. (2005) The ultrastructure and botanical aYnity of end-Permian spore tetrads. International Journal of Plant Science, 166, 87587. Reproduced with permission.) Fig. 6 End-Permian ozone loss and ultraviolet radiation-B (UV-B) fluxes. (Redrawn from Beerling, D.J., Harfoot, M., Lomax, B., and Pyle, J.A. (2007) The stability of the stratospheric ozone layer during the end-Permian eruption of the Siberian Traps. Philosophical Transactions of the Royal Society, Series A, in press.) Fig. 7 The ancient supercontinent Pangaea. (Adapted from Olsen, P.E. (1999) Giant lava Xows, mass extinctions, and mantle plumes. Science, 284, 6045. Reproduced with permission.) Fig. 8 Dramatic changes in carbon dioxide levels and global temperatures across the TriassicJurassic boundary. (Derived from data presented in McElwain, J.C., Beerling, D.J., and Woodward, F.I. (1999) Fossil plants and global warming at the Triassic-Jurassic boundary. Science, 285, 138690.) Fig. 9 Carbon balance of evergreen and deciduous trees in the polar winter. Fig. 10 Trends in global climate over the last 65 million years. (Redrawn from Zachos, J.C., Pagani, M., Sloan, L. et al. (2001) Trends, rhythms, and aberrations in global climate 65Ma to present. Science, 292, 68693. Reproduced with permission.)</p> <p>xiv</p> <p>Il l u s t r a t i o n s a n d p l a t e sFig. 11 John Tyndalls ratio spectrophotometer. (From Tyndall, J. (1865) Heat considered as a mode of motion. Second edition, with additions and illustrations. Longman Green, London. Reproduced with permission.) Fig. 12 Global warming in the early Eocene caused by greenhouse gases other than carbon dioxide. Fig. 13 The global rise of C4 plant dominance in terrestrial ecosystems. (Graphs redrawn with data from Cerling, T.E., Harris, J.M., MacFadden, B.J. et al. (1997) Global vegetation change through the Miocene/Pliocene boundary. Nature, 389, 1538; Cerling, T.E. (1999) Paleorecords of C4 plants and ecosystems. In C4 Plant biology (ed. R.F. Sage and R.K. Monson), pp. 445 69. Academic Press, San Diego.)</p> <p>PlatesPlate 1 A fossil of Cooksonia. ( The Natural History Museum, London. Reproduced with permission.) Plate 2 The leaXess and the leafy. (Upper image : from Osborne, C.P., Beerling, D.J., Lomax, B.H., and Chaloner, W.G. (2004) Biophysical constraints on the origin of leaves inferred from the fossil record. Proceedings of the National Academy of Sciences, USA, 101, 103602. Lower image: courtesy of Colin Osborne. Both photos reproduced with permission.)...</p>