Sharply criticising Darwin's contemporaries and successors for clinging too resolutely to the notion that Nature's forces merely creep along, Benton notes the persistence of one theme. The "uniformitarians", he says, blinded scholars to the evidence - evidence that suggested life could end suddenly. Charles Lyell, one of Charles Darwin's inspirations, argued that what is seen today typifies the entire, and lengthy, history of our world. Slow, gradual change on today's surface is but the most recent example of the panorama of millions of years. Sudden change, "catastrophism", promoted by Baron Cuvier in France, was false. In life, Darwin's evolution by natural selection reflected the gradualist theme.

Benton dismisses Lyell and his adherents as overcommitted to gradualism. He contends they shut their eyes to contrary evidence. He admits the data was less than readily apparent, but argues some questions should have been raised long before now. New research, sometimes in places already once observed, finally brought reassessment. The Ural Mountains in Russia offered the first clues. Roderick Murchison toured there in the 1840s, naming the "Permian System" of rocks. Wars and revolutions interrupted the surveys and geologists and paleontologists peered at new ground. The Great Karoo of South Africa, China and other sites provided new information. A gradually emerging picture revealed a massive die-off 251 million years ago. What had happened?

After a long introduction of chapters recounting the researchers and their findings around the planet, Benton dismisses the notion of a bolide impact. This idea, fostered by the discovery that the Dinosaur Era had likely been concluded by the impact of a 10 kilometre asteroid, wasn't matched by the evidence. While the Permian Extinction may have been accompanied by darkened skies and deluges of rain, the real killer was something else. The dinosaur extinction wasn't typified by massive intrusions of poisonous gases, but the Permian was another matter. Benton surmises that 251 million years ago a series of volcanic fissures spewed immense waves of lava over the land near the North Pole. This area, now known as Siberia, is still covered by the remnants of the outburst. With the lava came noxious gas, mostly carbon dioxide and sulfur dioxide. These "greenhouse" gases warmed the seas, releasing life-killing methane. The catastrophe may have killed off up to 96% of all living things.

This is not simply an arcane analysis of events in the ancient past. It's a book that should gain a wide readership, since the events of all those millions of years ago have implications for today. Benton notes the sediments at the bottom of our seas contain a build-up of methane equalling or exceeding that of the Permian. Today's human-spurred global warming may be leading to the same scenario. Extinction, Benton reminds us, isn't limited to dinosaurs or other ancient life. It is clear that we must learn how these mechanisms work to make rational decisions about our dealings with the biosphere. [stephen a. haines - Ottawa, Canada]