Cosmic love child is happy accident

Nature is a postmodernist author who seldom produces tidy narratives. But fortunately scientists are on hand to edit her script into potboilers - and there are plenty lurking in the 4.5 billion-year history of our planet.

Richard Southwood chooses one for The Story of Life , while Michael Benton picks another for When Life Nearly Died . Both are superb books that tell gripping tales about what has shaped life on earth.

Every good story needs a protagonist overcoming obstacles as they work towards a goal. In The Story of Life , life is the hero and Homo sapiens the goal. In fewer than 300 pages, Southwood chronicles the journey from primordial ooze to the anthropology of our recent ancestors. But while this in a sense is our story, the book avoids any religiously tainted notions that we are the pinnacle of evolution.

Compressing 3.5 billion years of evolution into fewer than 300 pages is an incredible feat, and Southwood somehow manages it without taking any shortcuts. The text flows effortlessly, spinning contemplative eddies in the mind of the reader. The book grew from a first-year zoology course at Oxford University, but its appeal is much wider than purely academic. No one with the vaguest curiosity about some of the big questions, such as "where do we come from?" and "how does nature work?", would regret reading it.

As the book steps deftly between biology, chemistry and geology, there are perhaps inevitably some tiny slip-ups. Southwood describes life around deep-sea volcanic vents, for example, as a food chain based on an oxygen-free environment. But the animals living at vents use oxygen, as do most of the microbes that nourish them. The blood of spectacular vent tubeworms, for example, is remarkably adapted to carry both sulphide and oxygen to the bacteria that live inside them. But that is a minor quibble. The scope of The Story of Life is breathtaking.

Richard Dawkins once suggested that aliens visiting the earth might judge our development by asking: "Have they discovered evolution yet?" Unfortunately, those aliens would get the wrong idea if they landed in some corners of the US, or even some parts of the UK where creationism is seeking a toehold. I hope that they land near a bookshop stocking The Story of Life . And as an exceptionally readable summary of the history of life on earth, it should be recommended reading for any non-biologists drafted in to teach biology in schools.

Evolutionary history is often regarded as involving long periods of relative environmental calm punctuated by brief spells of extreme disruption. Southwood likens this process to a kaleidoscope being held still so that patterns form and persist, then shaken to dissolve those patterns and replace them with new ones. The "shakes" of the kaleidoscope are mass extinction events, triggered by cataclysms such as the asteroid impact or similar catastrophe that wiped out the dinosaurs 65 million years ago.

Benton focuses on another of these, at the end of the Permian era 250 million years ago, in When Life Nearly Died . Rather than tackling 3.5 billion years of evolution for his book, Benton homes in on events that took place over just a few million years - the blink of a geological eye - but that had far-reaching consequences. Although this subject seems narrower in scope than The Story of Life , piecing together events so long ago in such detail is just as great a challenge.

The title of the book is dramatic, but rightly so. About 90 per cent of animal and plant species living at the time were wiped out at the end of the Permian era. Although much less appreciated than the mass extinction that saw off the dinosaurs, the end-Permian catastrophe was more severe and cleared the way for those popular lizards to rise to prominence. But who - or rather what - dunnit? Benton's book is in part a geological detective story, but with a rich historical backplot. He finally names a culprit in a denouement worthy of Hercule Poirot, which I certainly would not want to spoil by naming any of the suspects.

The protagonist in the first few chapters of When Life Nearly Died , however, is perhaps the concept of catastrophism itself - the idea that apocalyptic accidents play a major role in evolutionary history. Although geologists were gathering evidence for this idea in the early 1800s, the influence of Charles Lyell relegated catastrophism to the status of heresy in British geological circles for nearly 150 years. Benton's excellent historical treatment of this provides a useful example of how science is a human enterprise, sometimes dictated by strong personalities.

In later chapters, Benton gives an account of his own involvement in piecing together the end-Permian puzzle. This includes a fascinating travelogue, describing fieldwork in Russia just after the collapse of Communism in the early 1990s. Benton's style is personal and intimate throughout the book, overturning the stereotype of the dispassionate scientist. At one point, for example, he tells of how he first became interested in geology. Rather than distracting from the main thrust of the book, these anecdotes are an interesting window into the life of a scientist and what they do from day to day.

Having presented his case for the likely cause of the end-Permian catastrophe, Benton paints a picture of what it would have been like to live through it and the environmental consequences that rumbled on afterwards. This is described from the perspective of Dicynodon, a medium-sized plant-eating reptile abundant at the time. Benton manages to make this account compelling but avoids descending into pseudo-wildlife-documentary cheesiness. And he readily admits that his model may not be the last word on the subject, providing a refreshing example of how scientific understanding is provisional rather than dogmatic.

When Life Nearly Died highlights the role of catastrophes in shaping life on earth, while The Story of Life covers other processes that are also important in evolutionary history. But in a sense, accident and error are persistent themes, whether on the scale of an asteroid hitting the earth or changes to a DNA molecule. Any physicists who subscribe to the strong anthropic principle - that intelligent beings capable of appreciating cosmology are inevitable when the physical constants of the universe are set at certain values - would also do well to read these books.

Some palaeontologists, including Simon Conway Morris, believe that intelligence is an adaptation likely to appear in some form, whether human, dolphin, octopus or termite. But our particular species is a cosmic love child, born out of a chain of coincidences and chance events. As Stephen J. Gould remarked, we might easily not appear if the story of life were re-run. Although we are peculiarly intelligent apes, anyone who thinks there is anything more special about Homo sapiens needs to get over themselves.

The other theme common to both books is that of earth system science. Understanding how the living and non-living components of our planet interact, how they behaved in the past and what might happen in the future, requires a multidisciplinary effort. So earth system science is a broad church spanning biology, ecology, geology, geophysics and geochemistry. It has become the watchword of one of the UK research councils, but the curriculum in secondary schools seems to prevent pupils from recognising that the traditional boundaries between science subjects do not exist in this enterprise. As a result, sixthformers are perhaps less well informed than they might be about where particular subjects at university could take them.

Both The Story of Life and When Life Nearly Died demonstrate the interactions between biology, geology and chemistry involved in answering questions about our planet's past. As both books are very readable even at sixth-form science level, they might encourage thinking outside the boxes of curriculum and assessment.

Southwood and Benton display the hallmarks of excellent university lecturers through their writing. Their enthusiasm for their subject is infectious, and they handle concepts with dexterous flair. Like the best lectures, the books are also bang up to date, with some footnotes in The Story of Life flagging relevant scientific papers that appeared while the book was in press.

Scientists are traditionally derided as poor communicators, but these two certainly challenge that view. Their writing is as accessible and engaging as any popular book by academics in other disciplines. A quick glance at the bestseller lists shows that history sells, thanks to the likes of Simon Schama and David Starkey. Natural history books like these deserve to be up there with them.

Both books close with balanced discussions of the future for life on earth - and in particular the impact we are having on the world around us. With extinction rates rising as habitats are destroyed, we might be heading towards a catastrophic event of our own making. Neither of the authors are pessimistic, but nor are they complacent. Life eventually bounced back from the end-Permian catastrophe, although the bounce took several million years. Some species will survive whatever catastrophe we might devise, and Southwood's kaleidoscope will fill with a new pattern.

The "life" of both titles refers, by the authors' own admissions, to complex multicellular life like us. Although this perhaps seems anthropocentric, it reins in the subject and makes it more immediate. But we share our planet with other forms of life whose impact and achievements far outstrip our own. The Great Wall of China, for example, is often celebrated as a man-made structure that can supposedly be seen from orbit.

But there are life forms around us whose handiwork can be seen from a couple of solar systems away. These life forms are the microbes that govern the global cycles of chemical elements, giving our atmosphere a tell-tale signature that we are now squinting to see on planets around other stars.

Microbes had this planet to themselves for around 2.5 billion years before multicellular life such as ourselves appeared. And despite our own technology, we could not annihilate them completely, even if we were to split the earth apart. They are the real rulers of the world, and their tale is the secret history of our planet. But that is another story.

John Copley is teaching fellow, School of Ocean and Earth Science, Southampton University.