Nicholas Lezard's paperback choice: Reading the Rocks by Marcia Bjornerud

Reading the Rocks: The Autobiography of the Earth

by Marcia Bjornerud

(Basic Books, £14.99)

The idea of an exciting book about geology may be stretching the imagination to its limit, but we should be prepared to listen to anyone who is a master of their subject - any subject. And the subject of geology is one that concerns every single one of us: for geology is the story of our planet. With four and a half billion years of Earth's existence to cover, geologists have their work cut out. "Pages, if not entire chapters, of the Earth manuscript remain undiscovered," writes Bjomerud; "to those involved in the translation process, every pebble on the beach is a scrap of text from this immense and venerable tome, and it seems almost rude to ignore what these objects are saying."

There is, though, a particular urgency to comprehending earth's past. The story of the planet is coming, right now, to something of a cliffhanger: and it would be helpful to know something about what the planet did the last time it found itself in a fix. The geological record shows that there have been some very dire situations indeed. About 750 million years ago, the planet froze over completely. This is still a matter of conjecture - not least because no one could work out how the earth recovered. There are some good theories, though, and the evidence is there. Nearer to our time, towards the end of the Permian period, around 250 million years ago, an estimated 90% of all species became extinct. Unlike the event which killed off the dinosaurs - generally accepted to be a meteorite impact - this one was generated by the earth itself. We're still not sure exactly what happened, but it seems to have been a combination of factors - a massive temperature rise combined with two huge belches of carbon dioxide and methane. "Nothing larger than a house cat walked across the Permian-Triassic boundary, and the terrestrial ecosystem did not recover for as much as 5 million years."

As you might have gathered from that detail about the house cat, Bjornerud has a gift for the striking phrase and, elsewhere, for the telling analogy. These are handy when getting the science across, but sometimes what she has to say is so mind-blowing no embellishment is necessary. The idea of oceans so saturated with carbon dioxide that they were almost fizzy, or of magnetic poles flipping over at unpredictable intervals (we might be experiencing this soon - the geomagnetic field strength has declined sharply during the past 150 years), or of Venus being hit by an object so large that it reversed its direction of rotation, make the head spin. You may also get a little alarmed. When writing of the possible shutting down of the Gulf Stream, she alludes to the film The Day After Tomorrow: "The film's timescale is absurdly compressed, but the underlying science is sound." (The Core, though, in which a group of "terranauts" burrow into the centre of the earth to fix a geomagnetic crisis, she wittily dismisses as "literally abysmal".)

The wonder of this book is how, in a scant 200 pages, it covers so much ground. (So to speak.) Extinctions, mineralogy, mitochondrial DNA, the linguistic roots of geological terms, volcanoes, earthquakes ("earthquakes don't kill people," joke seismologists, "buildings do") - it's all here, and much more, delivered in prose that can often be ringing or, when occasion demands, amusing. Bjornerud has a great eye for both the big and small pictures; not only about geology at the levels of both molecules and mountains, but how the biosphere is affected by it. She is also very good on the history of geology, and how our attitudes to the planet have changed. For a scientist, she has a very welcome wariness about the dangerous limits of science. The arrival of human self-consciousness, she points out, is as dramatic a change in the biosphere as predation - that point in history when organisms stopped soaking up nutrients or sunshine to live, and started to eat each other, or be eaten. Those of you who have a rudimentary grasp of the Gaia hypothesis - that the planet is itself a self-regulating organism - will find it a lot firmer.