The book is a geological and evolutionary history of the planet, going backwards, starting 20,000 years ago and proceeding by leaps and bounds to 550 million years ago. Each chapter focusses on a particular location on the planet, mostly it seems because of the richness of the fossil record for that particular era. His style is something of a nature documentary, describing the environment you might have encountered, the sights and smells, the climate and the flora and fauna. All the time he links it forward to our own 'land', finding similarities or pointing out significant changes.
Very quickly (in book terms, not in years) you are back in pre-history, and the animals are outlandish. This is a Tully Monster, Tullimonstrum, described thusly in the book: "They have a segmented torpedo of a body, and at the rear, two rippling fins that look a little like the wings of a squid. At the front, a long, thin feature, something like the hose of a vacuum cleaner, wiggles, with a tiny tooth-filled grabbing claw at its end. Adding further confusion, there is a solid bar running from side to side across the top of the creature, horizontal stalks on which are set bulbous organs of some kind, which are generally assumed to be its eyes. All in all, it is unlike anything else that is known in over half a billion years of animal evolution." (p.195) But sometimes it seems as if everything he describes is unlike anything else. I don't know very much about evolution but I think the book helps get across the timescales that are involved. The process of a species adapting and being successful takes millions of years, and yet, confusingly, it can be observed in action in fruit flies. Again, he links forward constantly, telling you which modern creatures are related to the ones he describes. Incorporated into the history and the palaeobiology there is plenty of other stuff to learn. Here, when discussing Prototaxites, he diverts into a description of how fungi operate:
"Fungi are the great collaborators of life, forming close associations with species so distantly related to them that we place them in distinct kingdoms. The most intimate association they form is with a photosynthesising organism, whether a plant or a cyanobacterium, to form a lichen. Excellent at breaking down organic matter, the fungal partner in a lichen can extract huge amounts of mineral nutrient from even the barest surface, sharing it with a photosynthesising partner (known as a photobiont) and protecting it with a tough tissue sheath. In return, with access to light, the photobiont can make energy that will feed the fungus. This powerful combination means that, wherever there is a surface exposed to light and water, a lichen can grow." (p.208-9)
Here he teaches me about ancient mollusc, this one being most curious. It was thought to be extinct for several hundred million years, then a living specimen was pulled from the deep ocean by a fishing vessel in the 1950s. It is fascinating how some creatures are transformed over time and some find their niche and just stay there, barely altering.
"Monoplacoophorans are an extremely ancient type of mollusc, the oldest known from the fossil record. With a single, central, rippling foot, they shuffle around in the sediment. Wherever they go, they leave behind the scratchings of their rasping radulae, filing at the rocks to prise off their microscopic food. Monoplacophorans still survive in the present day, but where most fossil monoplacophorans live close to the shore, today they only exist in the deep ocean. The earliest of that group to venture into the deep, though, is Thermoconus at Yaman-Kasy. Perhaps, although the fossil record is to sparse to prove it, the monoplacophorans at Yaman-Kasy represent the beginnings of a retreat into the world where no others could survive, an evolutionary hiding place in an inaccessible niche-space, free of competition." (p.229-30)
As well as the flora and fauna each chapter tracks the transformation of the planet itself. It is easy to look at a map and assume that the world has always looked like this. I remember as a child learning how South America would fit against the coast of Africa and how the land used to be one huge continent. What I find from this book is that, as well as the massive changes in sea level, the land masses have had a long slow migration to their current positions that has taken them through many different configurations. He talks about how the crust of the earth is so thin, floating on a sea of magma: "The Himalayas have the thickest crust in the modern day, about 70 kilometres thick, but Mount Everest reaches only 9 kilometres above sea level. Mountains are tall because they have deep roots bobbing in the denser mantle. So much of our buoyant land is hidden below the surface. We, too, are walking on icebergs." (p.247) This (presumably artist's impression with some interpretation of data) shows the Devonian world (407 million years ago):
Here is a Promissum, a most ordinary creature, and here is the description of how it becomes fossilised (I borrowed this book without expectation and was continually fascinated by detailed information about the most random subjects):
"The rain of silt and algae that falls in the Soom summer also give the sea floor an unusual chemistry for fossil formation. If a Promissum dies in winter, it will sink to the bottom and become coated in and buried by that persistent subglacial black dirt. The body will decay, the teeth disappear, and nothing will be preserved. But in the summer, when the loess falls too, not all of it can be processed by the zooplankton and organic-eating bacteria, and it settles as a paler layer of rich sediment, enhanced by the organic input from dying plankton, a striped annual deposition called the varve. The preservation of this double-layering at Soom is an almanac, a yearly account of conditions some 440 million years ago, proportionally equivalent to having a daily diary for the earliest humans in western Europe, 1.2 million years before the present.
In the acidic conditions, the cartilaginous skeleton of Promissum will still decay, but other elemental forces will take hold. As the proteins in its muscles begin to disassemble, they release a chemical effusion of ammonia and potassium. Reacting with iron minerals, and dissolved within the spaces between individual sand grains, they turn into a rich illite clay. The shape of the muscle fibres determines the ultimate shape of the clay, and muscle is sculpted in mineral, replaced by its own facsimile. The conversion of soft muscle to clay at Soom is unique, and utterly beautiful, a vision of life in a sea that is advancing - as geologists defensively put it, transgressing - on the land, chasing the melting glaciers retreat." (p. 245-6)
The 'Big Five' extinction events also provide part of the structure of the book as they mark significant turning points for the balance of species, killing some and allowing others to become dominant. Another example of how well the book is written, explaining things without dumbing down (sometimes he assumed too much prior knowledge but not often). Apparently there is still debate about the cause of the Ordovician event, Thomas goes with the global cooling explanation:
"The algal blooms that still occur around Soon were ubiquitous, happening wherever these outwashes occurred, with bigger populations of bigger individuals. This glut increased the marine snowfall to the ocean floor from an occasional flurry to a continuous blizzard. As the algae's carbon-rich bodies settled and were buried, they drew with them carbon dioxide from the atmosphere. At the same time, a coincidental increase in volcanic eruptions as the Caledonides were raised produced a lot more silicate rock. As we have seen, the weathering of silicates causes reactions with carbon dioxide in the air. These fresh silicates helped to reduce the atmospheric concentration of carbon dioxide, too. In the resultant rapid climate change, a full 85% of the species on Earth, almost all marine, went extinct. The glaciation did not last long, but it was long -lived enough to cause devastation. It was the first of the so-called 'Big Five' extinctions, and the only mass-extinction event directly caused by global cooling." (p.241)
Evolution is a weird thing. I find it annoying that much ordinary writing about it makes it seem as if it were intentional, moving forward to some kind of 'ideal' lifeform, rather than a pure chance. A creature cannot 'decide' to evolve, or try and make itself suit a new situation. Then he gives me this lovely explanation of why it seems that evolution is something that happened in the past, but not so much any more:
"Perhaps, in the Cambrian and earlier, the development from fertilised egg to embryo to animal was less defined. If so, fundamental changes to tissues and their arrangements would be, on average, less damaging. Once fixed in place, though, fundamentals become very difficult to change. As with the functioning of a computer, fiddling with the code of a single application is relatively simple, and unlikely to damage the overall function of the machine, but editing a line from the operating system is likely to cause problems. Natural selection, then, ends up being a tinkering mechanism, unable - or at least extremely unlikely - to take a sledgehammer to the basic internal structure. In this view, a new phylum cannot arise in modern day because the anatomy of living beings is simply too complex compared with that of their Cambrian and Precambrian forebears. Evolution today can only be played out within the constraints set by the past." (p257-8)
And then we find ourselves back at the very beginning, and life, life is a chance chemical reaction in the depths of the ocean, which just makes it all the more amazing. My only criticism of the book would be that I found going backwards sometimes confusing, in that you were seeing the opposite of 'progress' with fewer simpler organism. The book became for me a little like looking at the stars and realising how small you are; looking at the length of time over which the planet has been transformed makes you appreciate how brief the human race's presence is in the grand scale of millions of years. Though it is not a polemical book in any sense his epilogue is a demand that the world pay attention to the past in order the understand the future.
"As far as extinction is concerned, the absolute climate is not to blame, nor is the direction of change. It is the rapidity of change that is important. Communities of organisms need time to adapt - if too much change is thrust upon them at once, devastation and loss in the common response." (p.241)
"Unlike past occasions when a single species or group of species had fundamentally altered the biosphere - the oxygenation of the oceans, the laying down of the coal swamps - our species is in an unusual position of control over the outcome. We know that change is occurring, we know we are responsible, we know what will happen if it continues, we know we can stop it and we know how. The question is whether we will try." (p.286)
He talks about how close the planet has come, more than once, to the destruction of all life, but I was left feeling that, actually, life is pretty damn persistent, even in the face of a pitiless and inhospitable environment it just wouldn't give up.
Stay safe. Be kind. Don't give up.
(Weird creature images from Wikicommons.)