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On Gaia

On Gaia: A Critical Investigation of the Relationship between Life and Earth

Toby Tyrrell
Copyright Date: 2013
Pages: 312
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  • Book Info
    On Gaia
    Book Description:

    One of the enduring questions about our planet is how it has remained continuously habitable over vast stretches of geological time despite the fact that its atmosphere and climate are potentially unstable. James Lovelock's Gaia hypothesis posits that life itself has intervened in the regulation of the planetary environment in order to keep it stable and favorable for life. First proposed in the 1970s, Lovelock's hypothesis remains highly controversial and continues to provoke fierce debate.On Gaiaundertakes the first in-depth investigation of the arguments put forward by Lovelock and others--and concludes that the evidence doesn't stack up in support of Gaia.

    Toby Tyrrell draws on the latest findings in fields as diverse as climate science, oceanography, atmospheric science, geology, ecology, and evolutionary biology. He takes readers to obscure corners of the natural world, from southern Africa where ancient rocks reveal that icebergs were once present near the equator, to mimics of cleaner fish on Indonesian reefs, to blind fish deep in Mexican caves. Tyrrell weaves these and many other intriguing observations into a comprehensive analysis of the major assertions and lines of argument underpinning Gaia, and finds that it is not a credible picture of how life and Earth interact.

    On Gaiareflects on the scientific evidence indicating that life and environment mutually affect each other, and proposes that feedbacks on Earth do not provide robust protection against the environment becoming uninhabitable--or against poor stewardship by us.

    eISBN: 978-1-4008-4791-4
    Subjects: General Science, Ecology & Evolutionary Biology, Physics

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-viii)
    (pp. ix-xii)
  4. Chapter 1 GAIA, THE GRAND IDEA
    (pp. 1-13)

    This first chapter introduces the Gaia hypothesis and two competing hypotheses.

    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 journalAtmospheric Environment, followed rapidly by two other papers both in 1974: “Atmospheric Homeostasis by and for the Biosphere” in the journalTellus, and “Biological Modulation of the Earth’s Atmosphere” in the journalIcarus.¹ James Lovelock was sole author of the first paper and coauthor with Lynn Margulis of the latter two. Both were already...

    (pp. 14-46)

    Much of this book involves examination of individual pieces of evidence relevant to the Gaia hypothesis. Later chapters will subject each of Lovelock’s three assertions (those just described in chapter 1) to close examination. The degree of match between the three competing hypotheses (Gaia, coevolution, geological) and the evidence will also be compared. Before all this can be embarked on, however, let us first look at the relationship between Gaia and natural selection. This is a search to see if we can understand why Gaia should occur. We are interested in whether there is any reason to expect something like...

    (pp. 47-66)

    Having established that, as far as we can tell, natural selection does not lead automatically to Gaia, this chapter starts using information about the present day Earth system to probe the conjecture that Gaia exists and is at the controls. The chapter focuses on assertion No. 1 (see chapter 1): the suggestion that the suitability of the Earth for life is strong evidence in support of the Gaia hypothesis. This first assertion is only about how suitable the Earthcurrentlyis for life. The puzzle of how it hasremained(orbeen kept) suitable for life is saved until later....

    (pp. 67-87)

    This chapter continues the theme of the last. The mission remains the same, to probe more deeply the Gaian assertion (the first assertion listed in chapter 1) that the Earth is exceptionally well suited for life. This claim will now be subjected to more detailed scrutiny in two companion chapters, this one and the next, focusing on one environmental variable in particular—temperature.

    One of Stephen Schneider’s comments to James Lovelock about the Gaia hypothesis was: “Jim, how can you possibly believe in Gaia when there are ice ages? if there was a Gaia it would stop them from happening.”...

  8. Chapter 5 ICEHOUSE EARTH
    (pp. 88-112)

    This chapter, a companion to the last, continues the investigation into whether life fares better on a colder or a warmer planet. This in turn is part of an examination of the Gaian assertion that the Earth is a comfortable habitat for life. Whereas the last chapter looked mainly at effects of temperature on present-day organisms and the rates at which they carry out activities, now the approach is to compare the life that evolution produced during past cold and warm climates of long duration. This allows us to overcome the hindrance that today’s life is inevitably well matched to...

  9. Chapter 6 GIVEN ENOUGH TIME . . .
    (pp. 113-129)

    Now I turn to examining Lovelock’s second assertion (chapter 1); namely, that the Earth’s Atmosphere is a biological construct that is distinctly different from any expected abiotic chemical equilibrium. This claim can be broadened to the wider claim that Earth’s environment bears the definite and considerable imprint of biological processes and is distinctly different from the environment that would be present if Earth did not possess life. We know that over geological time all of the water in the ocean passes through gills, all of the air in the atmosphere through lungs, and all of the soil through earthworm guts....

    (pp. 130-144)

    Having established that life has the power to shape the Earth, we can now move on to look more closely at the exact nature of life’s impact on Earth. The nature of this impact is most clearly seen following some major evolutionary developments, when a radical addition has taken place to the collection of life on Earth. What sort of environmental alterations do biological changes produce?

    In this chapter, we ignore externally forced changes and focus solely on internally generated changes due to evolutionary inventions of new forms of life. Sometimes change or variability in Earth properties is externally driven....

    (pp. 145-170)

    A main claim of the Gaia hypothesis (assertion no. 3 of chapter 1) is that the Earth is a particularly stable habitat for life, has remained so ever since life became abundant on the planet, and is stable in part because of the actions of life:

    The most important property of Gaia is the tendency to keep constant conditions for all terrestrial life. (Lovelock 1979)

    Gaia theory predicts that the climate and chemical composition of the Earth are kept in homeostasis for long periods until some internal contradiction or external force causes a jump to a new stable state. (Lovelock...

    (pp. 171-198)

    The previous chapter examined the claim that the planetary environment has been particularly stable over time. Many instances of contrary evidence were found. But life has nonetheless survived, even if it may have occasionally (for example, Snowball Earths) been a close-run thing. in this chapter I will now describe why this persistence of life over such an immensity of time is, from one point of view, extremely puzzling, but from another, no surprise at all.

    As part of describing one view, I will explain why atmospheric CO₂ is susceptible to rapid change. As a consequence, the Earth could, in theory,...

  13. Chapter 10 CONCLUSIONS
    (pp. 199-218)

    The Gaia hypothesis is one of the best known of all modern scientific hypotheses. Many scientists have enthusiastically adopted it, while others have rejected it out of hand. It has attracted generous measures of both opprobrium and acclamation, bouquets as well as brickbats.¹ But which judgment is correct? In this book I have looked at the reasoning advanced in support of the Gaia hypothesis and have examined it to see if it withstands detailed examination and if it makes a strong case for Gaia. Does the hypothesis still seem plausible when subjected to close inspection and probing scrutiny?

    In this...

  14. NOTES
    (pp. 219-272)
    (pp. 273-276)
    (pp. 277-298)
    (pp. 299-300)
  18. INDEX
    (pp. 301-312)