Tyrrell - On Gaia: a critical investigation of the relationship between life and earth

On Gaia

ON GAIA

A CRITICAL INVESTIGATION OF THE RELATIONSHIP BETWEEN LIFE AND EARTH

Toby Tyrrell

PRINCETON UNIVERSITY PRESS

PRINCETON AND OXFORD

Copyright 2013 by Princeton University Press

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ISBN (pbk.) 978-0-691-12158-1

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TABLE OF CONTENTS

To Helen

PREFACE

IN 1972 JAMES Lovelock made an interesting proposal. Life is not solely a passenger on a fortuitously habitable planet, he suggested. Instead, life is at the controls of the planetary environment, and has been so down through the geological ages. Continued habitability of Earth, probably for more than three billion years, has not been a coincidence, he proposed, but rather life has kept it that way. In the thirty years or so since its inception, this Gaia hypothesis has variously inspired, infuriated, and intrigued a whole generation of environmental scientists. Today it is probably more widely credited than ever, although it by no means enjoys unanimous support. Articles about it appear in the pages of Nature and other major journals, prestigious international conferences have been devoted to it, and vast international research programs now address topics that Lovelock was one of the first to consider.

Many books have been written about the Gaia hypothesis, but this is the first to carry out a critical examination. Gaia is a grand idea, of awesome scope. But is it correct? In this book I dissect the hypothesis and examine in turn each of the separate lines of reasoning that have been put forward in its support. Each line of reasoning is individually subjected to close scrutiny. Although I have by now of course developed an opinion, at the start I was undecided and approached the hypothesis with an open mind. Here I lay out the results of my evaluation. The aim is to present a thorough and penetrating investigation in a cool and dispassionate manner, guided entirely by the available evidence and by careful logical reasoning based upon it. This book is therefore the opposite of a straightforward and uncritical paraphrasing of Lovelocks views. The emphasis instead is to be initially skeptical about everything, avoiding automatic unthinking acceptance of any viewpoints, whether for or against Gaia. Although the book reaches a clear conclusion, I set out the facts and arguments on both sides so that you can form your own opinion.

Dissecting a hypothesis as all-encompassing as Gaia requires this book to stretch across many different scientific specialisms. This book concerns itself with life, evolution, and ecology, as well as with geology and paleoclimatology. It also deals with all parts of the Earths climate system, including the living parts, the ice sheets, the atmosphere, the oceans, and the land surface as well as the rocks beneath it. This wide-ranging analysis takes into account the results of many different scientific studies, including curious findings from little-known corners of the natural world. Within this book you will encounter hummingbirds in Caribbean islands and the similarity of their straight or curved beaks to the flowers they extract nectar from, the puzzle of occasional misplaced large stones in otherwise exclusively fine-grained marine sedimentary rocks, Walsbys square archaeon from the Dead Sea, the everlasting durability of the waste that corals generate, and differences in the way that Australian snakes bear young depending on climate (they dont always lay eggs). The relevance of all these and many more individual observations is made clear.

The critical examination of Gaia in this book involves consideration of many details such as these, but also involves stepping back to appreciate the bigger picture that emerges. In terms of that wider view, this analysis of Gaia engages with some fundamental issues. The book maintains a tight-beam focus on evaluating the Gaia hypothesis and includes only topics that contribute to a deeper understanding of its plausibility. Nevertheless, during the journey we find ourselves pondering some of the great questions about the nature of our planet, its history, and how it came to give rise to us. This analysis throws up interesting insights and sheds light from new directions on questions such as: just how good a planet is Earth for life? what effect has life had on Earth habitability? and how is it that our planet has remained continuously hospitable for life over billions of years?

Some exhilarating recent scientific developments are covered. We know a lot more today about climate, the Earth system, and even the mechanics of evolution than we did when Gaia was first proposed in the 1970s. Research activity in Earth system science has burgeoned, and numerous scientific journals exist today that didnt at the time Gaia was first proposed. Our understanding has been improved and changed by discoveries of environmental and climate instability as revealed by gas bubbles in ice cores, fluid inclusions in evaporite deposits, and magnetic mineral orientations and dropstones pointing to Snowball Earth events. Our knowledge of the limits to life (extremophile tolerances) and of the effects of temperature on life and evolution has developed rapidly over the last few decades. Given that more than thirty years have passed since Gaia was first proposed, it is now an appropriate time to take stock of the hypothesis in the light of all of this more recent, and fascinating, information. In the context of this subsequent work, I ask the question: Does the Gaia hypothesis hold up in court? I bring the hypothesis face to face with modern evidence and undertake a skeptical but hopefully fair-minded evaluation.

On Gaia

Chapter 1

GAIA, THE GRAND IDEA

THIS FIRST CHAPTER introduces the Gaia hypothesis and two competing hypotheses.

1.1. A BRIEF HISTORY

Gaia, the idea that life moderates the global environment to make it more favorable for life, was first introduced in 1972 in an academic paper titled Gaia as Seen through the Atmosphere in the journal Atmospheric Environment, followed rapidly by two other papers both in 1974: Atmospheric Homeostasis by and for the Biosphere in the journal Tellus, and Biological Modulation of the Earths Atmosphere in the journal Icarus. James Lovelock was sole author of the first paper and coauthor with Lynn Margulis of the latter two. Both were already scientists of some note. Lovelock had already pursued a successful career inventing chemical instruments, including, most famously, the electron capture detector. This device, when coupled to a gas chromatograph, allows for the detection of trace chemical substances even at extremely low concentrations. Before that, Lovelock had worked for twenty years at the United Kingdoms National Institute for Medical Research in Mill Hill, London, carrying out research in biomedical science.

Use of the electron capture detector started to become widespread due to its great utility, and through his consultancy work with it Lovelock was invited to participate in a NASA project to work out how to ascertain if Mars contained life. The two Viking spacecraft, now revered in history as the first spacecraft ever to land on the surface of another planet, were just then being designed, and a major priority was to decide which instruments to put on board. Reflection on this problem of how to detect the presence of life stimulated Lovelocks first thoughts on the Gaia hypothesis.