Non-Fiction Reviews
Earth & Life
A four billion year conversation(2026) Andrew H. Knoll, Princeton University Press, £25 / US$34, hrdbk, i + 298pp, ISBN 978-0-691-18223-0
For the scientist into science fiction, or indeed the SF aficionado into science, science that is genre-adjacent – SF² Concatenation's two principal target readerships – is of special interest. Speculative Fiction deals more with big topics than day-to-day or 'mundane' fiction and with regards to life, planetary change across deep-time is as about as big as it gets with regards to life. And so Andrew Knoll's latest book is very likely to interest many of this site's regulars.
Knoll himself is a US university-based researcher into 'geobiology' – the area of overlap between biology and geology, but it is also known a Earth system science or an Earth system science approach to life's evolution. It might also be described as biosphere science, or even biosphere evolution. This last might be described as the 'co-evolution of life and planet' which in Britain was actually the title of a three-year NERC research programme that ran from 2011. From this you can deduce that this is both a genuinely respectable area of science and an area of research of current interest (there are other on-going research programmes into deep-time biological and geological processes and the interactions between the two. These interactions result in the co-evolution of life and planetary geology or, as Andrew Knoll puts it, the 'conversation' between the two. Indeed, we humans are one, a recent, result of this conversation and indeed we are – our species is – now having an impact on our world at a planetary scale and notably the global commons of atmosphere and oceans.
And so we come to Andrew Knoll's eminently readable book.
Before proceeding, I should point out that Earth system science is currently an exciting area of research with many questions being asked, ideas floated and hypotheses flying about being tested; more so than arrows at Custer's last stand. (I'll return to this later.)
In essence this book invites its readers to take a fresh look at how they consider the evolution of life and our planet. In one sense you can consider our planet forming out of the primordial solar cloud of dust and gas into a hot, molten ball of rock with assorted elements surrounded by an early (primary), thick atmosphere devoid of free oxygen, the condensation of water to form the oceans and the creation of a crust, the start of some form of plates and then proper continental plate tectonics with the ensuing cycle of supercontinent formation and fragmentation (the Wilson cycle) that enabled the deep time cycling of elements over many millions of years between the surface and deeper into the Earth.
On the other hand there is biological evolution with the rise of life and simple (prokaryotic) cells, and then their coming together to form more complex (eukaryotic) cells, the evolution of oxygen generating photosynthesis, and then multicellular life.
Instead, we should perhaps consider matters as being the co-evolution of life and planet with biology and geology evolving together. It is as if, the author muses, biology and geology are having a conversation with each other: one that takes place over billions of years. Remember from your school days that you were taught about things like deep-time carbon cycles and plate tectonic but that was in your geography classes. You were also taught about biological evolution, but that was done separately in your biology lessons. Perhaps it might be better if they were taught together? Irrespective of this Andrew Knoll encourages us to consider the interplay of, and the 'conversation' between, the two.
Earth and Life summarises this conversation. Along the way we get to see how the key elements that life uses are cycled through the biosphere. And so we get three chapters on 'The story of O' parts one to three (perhaps unfortunate titles considering the non-speculative fictional fantasy novel of the same title by Anne Desclos and its two sequel spin-offs) and chapters on other key elements and water.
We get to see the importance of the rise of plants as well as how a (comparatively) stable climate, and a chapter on close calls that recounts the two Snowball Earth periods before moving on to what we (humans) are currently doing to the planet. This neatly segues into a chapter on what we are doing and where we are heading in the 21st century.
Finally, there are two chapters on other 'conversations': one on Mars and one on life elsewhere in the Solar System and beyond around other stars. One of its conclusions being that the deep-time evolution of life and planet narrative (or conversation) that has taken place here on Earth has implications for life across the Galaxy.
Having said this, I personally think that one of this book's most important messages is how unique a time we are in now, today, and that in our species having a marked impact on the biosphere risks trashing our home. It is not that we will destroy the biosphere, but we may very well for a time (centuries or as likely many thousands of years) make life very uncomfortable for our species and our planet unlikely to be able to support the several billions of humans it now does.
As noted above, the past quarter of a century Earth system science and geo-biology has been a fertile area of scientific investigation and its researchers have been having lively conversations and on occasions somewhat vigorous debate. In many areas there have been rival hypotheses. For example, go back three decades and some might say that the two Snowball Earth's spurred biological evolution, but more recently some are considering whether life itself was a key factor along with geology and part of the cycle of plate-tectonic supercontinent formation and fragmentation. The author alludes to some of these debates but does not get the reader bogged down by them.
Andrew Knoll is an established figure in this field (I have come across several papers he has co-authored over the years) and with Earth & Life he has done a commendable job of introducing readers who may be interested in science but who are not professional scientists themselves: it is that straightforward a read. Having said that, some scientists – not least biology and geography school teachers – might benefit from Earth & Life. Meanwhile, undergraduates into environmental and combined science as well as other interdisciplinary science will also find this useful, especially as at the book's end there is an academic reference list linking to number notes in the main body of the text so enabling students further explore the academic literature.
Importantly, this book is a must-read for those undergraduates taking astronomy or astrophysics degrees with a module on exobiology.
Finally, as said, with regards to scientists into SF, and SF aficionados into science (both being SF² Concatenation's core readership) this pushes a good number of the right buttons.
Jonathan Cowie
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