Toby Tyrrell's "On Gaia"

Toby Tyrrell is professor of Earth system science at the National Oceanography Centre Southampton (University of Southampton).

He applied the “Page 99 Test” to his new book, On Gaia: A Critical Investigation of the Relationship between Life and Earth, and reported the following:

My book is an investigation of a scientific hypothesis, to see whether it is correct or not. The hypothesis that I subject to detailed scrutiny is the Gaia hypothesis, which suggests that life on Earth has helped to control the global environment, keeping it stable and comfortable for life. This is an important topic because we need a proper understanding of how Earth’s environmental system works, in order to be able to keep it habitable for us despite the massive changes we are imposing upon it, such as the 40% increase in the amount of carbon dioxide in air.

So how does my book stand up to the page 99 test? Page 99 is mid-way through an assessment of one claim put forward in support of Gaia, that the Earth is especially comfortable for life. In this chapter of the book I am in the process of showing how the data cast doubt on this claim (see also here). I have just finished showing that ice ages (the predominant climate state of the last few million years) are severely unfavourable times for life as a whole. Now I am considering whether past warm periods in Earth history were any better. The top part of page 99 shows a photograph of a Cretaceous-age fossil tree stump from Antarctica, where not even a single tree grows today. The fossil is of excellent quality and is unambiguously that of a tree stump. I like the way that this single fossil is able, by itself, to tell us that the Earth has changed over time. As it happens we now have a wealth of supporting evidence showing that forests spread much closer to the poles during past warm times on Earth, such as during the Cretaceous. Further examples, in the form of fossilised breadfruit and dinosaur bones in the high Arctic, give further evidence of past sub-tropical climates at high latitudes.

But on page 99 I am also discussing the limitations of fossil evidence, and the difficulties in working out past environments. In particular I am pointing out one such limitation: the difficulty in determining past vegetation when no fossils are left. It becomes problematic when whole ecosystems leave no trace of themselves. This is highlighted by describing how coal (with its abundant fossils) is not forming today beneath the Amazon forest.

Learn more about On Gaia at the Princeton University Press website.

--Marshal Zeringue