Non-Fiction Reviews

Revolutions that made the Earth

(2011) Tim Lenton & Andrew Watson, Oxford University Press, £29.95 / US$52.95 / Can$51.20,
hrdbk, xii + 423pp, ISBN 978-0-199-58704-9


Occasionally, very occasionally, a general science book crosses my desk that makes me drop everything: Revolutions that made the Earth is one such book. I immediately skimmed the contents to settle on an area of personal interest, but before I knew it I had finished that chapter, in the course of which was drawn to a reference a couple of chapters earlier and so read those too.   Big mistake! Suddenly I realised that a couple of hours had passed and that I was really going to have to go back to the beginning and read the book thoroughly from the start. When a book does that to you, you know you have something really special.

Before going any further, let me explain who might really benefit from this book (as after all if you are not one of those then this review – which I suspect may end up being lengthy – will not be of much interest).   First off, potential readers are going to have to have a background in undergraduate-level science, or at least be self-taught to that standard. It does not unduly matter in which science potential readers have qualified as the authors do a commendable job of bringing readers up to speed in the various (and there are a number) of specialist areas on which their case rests. So if you have a grounding in, and a real passion for, science writ large then this book could well be for you.  Second, the book will be of interest to anyone who wants to know about the geologically-spanning dance between life and the (global) environment. Third, this book is absolutely critical to those studying exobiology (or 'astrobiology' as newbie trendies call it) as it presents a solid case for some of the key features of Earth-like planets, and so has implications for life (especially complex life) elsewhere in the Galaxy (hence Universe) through an examination of our own world.

With regards to the core regular visitors to this site (scientists who enjoy science fiction and who, of course, can readily distinguish between the two), it is the evolution of the Earth's biosphere and its Earthlike exoplanet implications that may well grab them in addition to the science itself.  After all, a proportion of hard SF deals with issues in deep time (time over a geological scale) and with the state of whole planets.  Then there are SFnal issues such as the Fermi paradox of which the subject matter of this book has considerable implications, and on which the book itself briefly (very briefly) touches.

Additionally, this book will be of relevance to some scientists who have no interest in SF and here, in addition to exobiologists, those involved in biosphere (Earth system) sciences will find this an absolutely fascinating if not an essential read.

Hopefully the above two paragraphs will help you decide whether this book is for you. Those of you who know me will know that my interests encompass a number of the above areas. My own undergraduate textbook on climate change biology and human ecology (1st edition 2007, and 2nd currently being revised and expanded for 2013) devotes a good quarter to past climate change and a whole chapter on climate change in deep time. This is integral to understanding the current global warming issue because the evolution of life has affected our global climate and planetary state, and you need to be aware of this if you are to appreciate the significance of what our own species is now doing to the climate system and the consequential implications for the future. In short I am familiar with many of the science elements within Tim Lenton's and Andrew Watson's book.

To distil the authors' complex synthesis into a few lines is difficult, but in essence their case is this. Life arose (surprisingly) early in Earth's history before evolving. In doing so you may think that there are many evolutionary stages between life's origin and us (intelligent, technology-wielding) observers today: as the authors say, if you are reading this, you qualify as such an observer. However, as the authors convincingly argue, there are surprisingly only really only three key stages (perhaps several intermediate ones of lesser criticality/evolutionary difficulty), absolutely necessary to get from the origin of life to us as intelligent, third stage, technological observers. Furthermore, these key stages (the revolutions in the book's title) have some common features. These centre on carbon cycling (after all life on Earth is carbon-based) and how it relates to the global climate.

Now, while the above description may seem simple, the actual case they present is based on a considerable body of evidence gathered from disparate specialist areas of biology and geology as well as underpinned by some simple (if you understand the notation) yet intellectually challenging maths, not to mention observations gleaned from astronomy, all of which are thoroughly referenced. This book is a scholarly work. (And do not worry, you do not have to look up and read the maths papers referenced to follow the book's line of arguement.)

It has to be said that those without any background in science may well, if not will, struggle. This is not because the authors' argument lacks coherence, but because its supporting evidence-base is so broad and the authors do go into some detail (almost wonkishly so) in describing the key exhibits they use to make their case. Having said that, for example, they do give one of the best of the brief summaries as to how photosynthesis works I have come across over many years. Furthermore, there is nothing wrong in being wonkish if presenting an integrally complete case is the goal. Nonetheless, some may find the authors' rigour causing them to stumble in their reading. My advice is that providing you can cope with most of the book, it does not really matter if you skate over two or three of the chapter subsections. This is not a problem as the authors introduce each chapter as well as each of the book's sub-dividing parts. There are also end-chapter summaries. All of this means that it is possible to keep in touch with central case being presented even if some sections are simply skimmed by readers. (Readers can always go back to these later if they feel the need, and a complete reading of the book is to be encouraged.)

For the most part the style of writing is of the proverbial New Scientist level: perhaps occasionally dipping into Nature 'News & Views' complexity. (Nature's 'News & Views' section being the part of that journal that places subsequent research papers in that issue into a broader scientific context as well as providing an aid for those reading across disciplines.) Indeed occasionally, as with the book's first chapter, the writing style is positively Carl Sagan-ish. (I even checked Sagan's Cosmos to see if the authors lifted, or paraphrased, any text: they had not from what I could see from a quick peruse.)

Criticisms. Well most of my personal criticisms (being vaguely familiar with the ground they cover) are actually ones of nuance and not of disagreeing with the authors' central argument (for which I have more than considerable sympathy). For example, they dwell on Carter's ('Anthropic principle and implications for biological evolution', 1983) toy mathematical model, but then they stretch it more than a bit to breaking point: didn't the authors' parents ever tell them to be careful with their toys as Christmas and birthdays come but once a year? Indeed the pacing of the key critical stages in evolution (revolutions) I contend (and their own argument by implication positively suggests but they don't make that leap) is not likely to be as uniformly spaced through geological time as the authors hypothesise (sorry Andrew Watson). Furthermore, considering how much longer the biosphere is likely to remain supportive of complex life is irrelevant: the process of evolution and evolutionary speciation does not 'look' forward in time. (This dimension to Carter's original simple model is, I think, very weak and so by itself certainly not worthy of extrapolating its implications as to the pacing of preceding stages.)

(Considering how much longer the biosphere is likely to exist was an artefact in part arising out of Carter's (Copernican) toy model's good-starting-point presumption that there was nothing special about the Earth as a complex life-bearing planet. Therefore, after the first iteration of considering the toy model it really is not worth trying to read more into it: diminishing returns etc. The key point is that critical/difficult evolutionary stages are not many – as is commonly thought – but few – as Carter and the authors (I believe rightly) conclude.)

However, as I said, this disagreement of mine is simply nuance and not a criticism that undermines the thrust of the authors' case or their core conclusions as to the relevance of where we are now in a globally warming world. Indeed for the most part the book is carefully written and some readers may not notice the caveats and wriggle room given as the science is presented. Yes, there are caveats and wriggle room for much of the evidence presented but this is because science is an on-going endeavour, and research into life, the Universe and everything is incomplete. Yet the book's writing in this regard is carefully crafted so that if you are unaware of the science being discussed you will not notice the caveats, and if you are you can marvel at the stepping stones the authors choose in crossing the river of scientific uncertainty.

Let me give you just one example just so you understand what I mean.  On page 370 the authors (rightly) say:   "More controversially, it has been suggested that carbon dioxide released from biomass and soils, and the methane released from domesticated cattle and the creation of paddy fields began to affect the composition of the [Earth's] atmosphere as early as 8,000 years ago."  Now this statement is true, because such a proposition as to the cause of the significant change in atmospheric methane taking place thousands of years ago (in the early part of our current 10,000 year Holocene interglacial) has been made and indeed gained some traction in the academic literature. The authors' caveat and wriggle room comes with their wording 'more controversially'. Blink, and you might miss it but such caveats are important to those versed in the relevant science. Indeed, when those of us first heard that particular proposition (humans affected the global system 8,000 years ago) it did seem interesting and for a minute it was an attractive notion: until that is you do a back-of-an-envelope calculation.  Say, assuming intense primitive agriculture that every human on the planet at that time – less than 200,000 (compared to the around 7 billion now (2011)) – owned a cow in addition to (and not replacing) a wild cow (and surely domesticated cattle grazing areas did mean that some wild ruminants were replaced rather than just displaced), and also wildly assuming that, say, a third of the global population cultivated a hectare of rice paddy, then you can quickly see that difference in methane was tiny compared to the fluxes from natural wetlands. So after just a couple of minutes' thought some of us found the notion of such early human global impact difficult to swallow, but because the idea of such early human impact had been published in a peer-reviewed journal (in 2003), many uncritically accepted it. (And indeed I had a brief e-mail exchange with a BBC TV documentary presenter – a qualified geology professor no less – who seemed to uncritically accept it as fact and not even worthy of debate: how can any self-respecting scientist do that; Carl Popper would spin.) The thing is, as the authors recognise, even if it is debatable – and the authors rightly signal this with the word ' controversially' – that humans were significantly impacting on the global carbon cycle 8,000 years ago, what is certain is that our species is certainly having such an impact today!  So in Revolutions that made the Earth the authors have done an excellent job of quietly signalling such debate, knowledge-gaps and so forth, without unduly interrupting their narrative's flow .  Such wriggle room and the caveats do not undermine what the authors are saying because the volume of evidence they cite is considerable and their case robust. So, even if evidence for some detail in one area of science is missing then it is often covered by other evidence elsewhere: again this is why readers do need to have a basic undergraduate understanding of science to get to grips with the book's massive information dump. Consequently, the wriggle room and caveats are to be commended because they really do demonstrate that the authors genuinely are acutely aware of the debate surrounding some of the evidence as well as where there are significant gaps in our understanding: this is science hypotheses generation from its cutting edge.

Now, I had wondered why the authors had not provided a simpler account for a wider readership, and the answer here (I think, and I admit I may be wrong) is that the authors are doing two things that editorially do not entirely lend themselves to each other.   The first is that they are presenting a reasonably fresh approach to the story of life's evolution and the planet. Though many of the elements of their case have been around for a while (the book is amply referenced) I have a feeling that this book is the first coherent presentation of this 'critical carbon life evolution revolutions' picture, and for which the authors truly deserve credit. (Previously there have been papers, articles and books that in part refer to such a few number of critical steps but this book I think is the first devoted exclusively to this.) And so in part the authors are speaking to fellow academics and this is them nailing their flag in book form to the academic mast.  The second thing they are doing, which is quite different, is providing a fascinating story that will appeal to many aficionados of popular science books. Indeed while there are countless books on 'early' life especially dinosaurs (which actually are late-comers), this book pays considerable attention to really early life before the Cambrian boom (around half a billion years ago) and how it is we know what we do about such truly ancient times back to over 3.5 billion years.   The difficulty comes is that speaking to fellow academics, and also conveying a message to a broader readership, arguably does require two different levels of comprehensibility: catering for both is not easy. Time will tell, through the book's sales, how well the authors have succeeded in both these disparate missions.

Yet, as hugely worthy is this book, I am though a little disappointed that a number of simple things were not done.   Why on Earth was not a geological table included?   Why were not abbreviations spelled out in their first usage within each chapter? (Most readers do not sit down and read all the way through in one go but episodically, perhaps on the train, or at weekends or whatever. Also students, and those having read the book once, subsequently mostly just dip into bits for reference when writing essays or checking some fact, and yet while some abbreviations were listed at the front, not all were.) So repeating abbreviations in full once in each and every chapter of their use is simply courteous. (Many copy editors I know tend to go for the citing abbreviation in full just once when first used in a book, so maybe this was not the authors' fault but all-too-common publisher sloppy house style: OUP should know better.) Then again, why was common alternative nomenclature when it does happen not at least mentioned: for example IETM and PETM*? ('Google scholar' these and 'climate change' you will see that there are some differences in the papers your respective searches pick up.)   Why, when mentioning any geological time by name, was not the relevant date also given in brackets after? For example, the end-Cretaceous extinction (65MYA) – MYA being 'millions of years ago': this really does make it so much easier for those unfamiliar with geological nomenclature and would have not been hard for the authors to do rather than expect readers to pick up and remember geological ages.  And then there were the occasional contradictions. For example, on page 50 we are told that stellar synthesis did not favour nitrogen which is why nitrogen is a potentially limiting nutrient for plant growth, but then the next page it is pointed out that the atmosphere is awash with nitrogen but it is its triple N-N bond that's the stumbling block.  Then again on page 383 we are told that global population is set to stabilise between 8 – 10 billion, but on page 399 are told it will be at least 10 billion by the end of this century.  Now most books (and my own writing is no exception) have typos and tiddler mistakes, but outright contradictions are not only annoying but do confuse and particularly so when speaking to those across disciplines. Arrghhhh!

(And I am not going to mention my bugbear in loathing the term climate 'tipping-point' as this suggests that there is a specific 'point' about which the climate shifts to a new state and that returning to that 'point' will flip the climate back again. This is not always true: often it is not. Climate 'threshold' is a more representative term. Sorry Tim Lenton... And yes I did just mention this bugbear.)

One thing the authors were less than clear about in their diagrams was the number of Snowball Earths. Their text makes it clear in several points that there was an early Snowball Earth around the time that aerobic photosynthesis first really got a head of steam. (Actually, as the authors correctly say, a series of a number of Snowball events over a few million years but these can be considered a single Snowball Earth (clutch of events) which we might call Snowball Earth 1 when taking the broad, more than three-and-a-half billion year, perspective of life on Earth. And then, again, as the authors also often mention in their text, there was another Snowball Earth (again a clutch of episodes) before the Cambrian evolutionary explosion of multi-celled animals and this we might call Snowball Earth 2. Yet the authors' text notwithstanding, the first Snowball Earth is not included in their central timeline diagram depicted on the inside front cover (and repeated on the inside back). Yes, Snowball Earth 1 is presented as the 'Makganyene' Snowball Earth on figure 2.3 but this section of the timeline does not include Snowball Earth 2 as it does not extend that far. Meanwhile the reverse is true of figure 2.4 which depicts what the authors call the Sturtian and Marinoan Snowball events (which the text instead refers to as at the end of the Proterozoic) and which the authors might have called the Snowball Earth 2 (clutch of Snowball events). In short there is no diagram that depicts both Snowball periods.  And please, if we are going to use undated geological nomenclature can we at least include the ones we are all meant to work from: the International Stratigraphic Chart provided by those nice folk at the International Commission on Stratigraphy (ICS): they even have a website with a free chart you can print out. Indeed the time around Snowball Earth 2 the ICS call the 'Cryogenian', a name that really does imply that the global temperature back then was a tad on the nippy side. Sub-divisions of the Cryogenian can then be additionally cited in the text along with their MYA dates.

Now I mention that the book needs a little tidying up not to have a go at the authors but because this book really is so important that it will no doubt get a few printings and in time will hopefully deserve a new revised edition. Rather than its simple reprinting, this last will be necessary as new science will have since been added to the picture the authors present. Indeed for instance, since this book was published – and to return to the early-human significant influence on atmospheric methane thousands of years ago example – new evidence has been presented that further supports back-of-the envelope calculations that suggests this early agriculture, methane proposition really not only 'controversial' but downright unlikely. In February (2011), subsequent to Revolutions that made the Earth's publication, Joy Singarayer, Paul J. Valdes, and colleagues from Bristol, Exeter and Sheffield Universities in Britain used a new computer model of the Earth system that successfully did something earlier models did not: it successfully reproduced the atmospheric methane levels we find in ice cores from  both  before (i.e. during the last glacial (ice age)) as well during the current Holocene (warm) interglacial. Their work (Nature, 470, 82–85) fairly firmly suggests that the early Holocene 8,000 years ago methane sources are predominantly natural and not human-induced (anthropogenic). (Singarayer and Valdes may be applauded for their computer modelling, but I give a cheer for good old back-of-the-envelope calculations that again demonstrate that you really do not need a big research budget to be truly in the game regarding the latest science thinking, and personally I am pleased when the big boys get around to support my own individual musings.) So one can see that, in say five or six years time, with more new science results like this relating to other areas of the book that the book will warrant updating. In fact this is more than likely as the UK Natural Environment Research Council is funding a five-year 'Long-Term Co-Evolution of Life and the Planet' research programme, so you can bet your cotton socks that there will be a lot of new science coming out of this. In short, I truly hope that there is sufficient sales demand for this book that we do get such a revised edition and that the authors take that opportunity to tidy up their groundbreaking text.

As mentioned, this book's science draws upon many disciplines.   Indeed while there is much corroboration across disciplines in some areas (such as physics and material science, or ecology and meteorology) I have found in my work of many years with learned societies that it is surprisingly difficult to get scientists from different backgrounds to actually take time to engage with each other, even if generally we all think it would be a good idea to do so. Indeed, the authors of Revolutions that made the Earth do wonder (p77) why the afore-mentioned 1983 Carter paper (toy mathematical model) on critical evolutionary steps (that surprisingly suggested there were only one or two steps) was largely ignored by biologists. The authors wonder whether it was because Carter's conclusion was so surprising that biologists dismissed it, or more likely was it because that biologists do not read journals that specialise in physics and astronomy: Carter's paper was published in the Philosophical Transactions of the Royal Society Transactions A. Here personally I can say that as a life scientist I am a Trans. B person (not Trans. A) and that my research paper reading outside of biology, geology and environmental science journals (so as to get my non-life-science fix) comes from Nature (best multidisciplinary journal) and Science (the multi-disciplinary journal with the best science writer, Richard Kerr). Furthermore, I am not familiar with mathematical notation and so (I freely admit) I initially struggled a little to get through Carter's paper when I first found it nearly a couple of decades after it was published, and (perhaps I am being vain here) this despite my having a fairly broad science perspective: there is only so much reading I can do. In short, I am not surprised that few scientists have the breadth of vision as in this Earth systems case have the authors of Revolutions that made the Earth. But then this multi- and inter-disciplinary approach is one of the book's strong points and I bet that nearly all scientist readers will gain some new insights.

By now you will have gathered that, despite the need for a little sprucing, I firmly commend this book and await to see if it sparks new thinking in biosphere evolution in wider scientific circles. I do hope so because there is much of the 'conventional view' that should have been put to rest over a decade ago. (Sadly I have still seen the old conventional view promulgated to the unsuspecting public on a number of recent (2007 – 2010) TV documentaries, and I even gave up half-way through a two-day Carlton House Terrace symposium a few years ago because so much of the discussion pointlessly focussed on hydrogen peroxide formation in the Snowball Earth 2 ice sheets (purportedly to in turn provide the oxygen to get the Cambrian boom going): fortunately Lenton and Watson spare us that particular torture.)   Meanwhile if you are up for a polymath science intellectual tour de force, and are interested life's evolution on potential Earthlike planets, then this book is a real treat. As regards the specialist, if you are working in exobiology (or even astrobiology) then Revolutions that made the Earth really has to be an absolutely essential, 'must read'.

(Yes, as I suspected at the start, this really was going to be a lengthy review. My thanks to those of you who made it this far to the end.)

Jonathan Cowie


*IETM stands for Initial Eocene Thermal Maximum (to distinguish it from what is possibly the Eocene Thermal Maximum that took place a few million years later). This climate event took place at the beginning of the Eocene roughly 55 million years ago. Conversely PETM stands for Palaeocene-Eocene Thermal Maximum and those that use this term consider that the climate event did not take place entirely at the start of the Eocene but straddled the Palaeocene/Eocene boundary. Now, certainly this event generated geological strata that marks the transition between the Palaeocene and Eocene (a basal Global Boundary Stratotype Section and Point). But this IETM or PETM question is a bit like arguing whether the boundary strip land between North and South Korea actually belongs to North or instead alternatively South Korea? Unless you are pedant (or a stratigraphic expert) this no-man's land debate is trivial and inconsequential, but you (the unsuspecting book's reader) do need to know both nomenclature terms if you are inclined to follow up this avenue the book covers by engaging in your own searches of the literature and discussion on the internet as many science papers use one or other of the terms: few use both but you need to use both if your Google Scholar searches are to pick up both cadres of papers.

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