A paleontologist stalks a mass murderer

The Gorgon was the top predator of its day, taking down strange beasts the size of a modern hippopotamus. The first man to find one called it Gorgonopsid, after the mythical Gorgon, a creature so horrible that all who gazed upon it were turned to stone. The animal stood 10 feet from tip to tail. Its head was tiger-like, with four-inch teeth designed for slashing prey. And yet it was eerily not like a tiger at all because the eyes were set at the sides of the head like those of a lizard, and the huge body was covered with scales.

In a tale of science and discovery that reads like a whodunit, Peter Ward tracks the answer to the question: Who killed the Gorgon?

It's an important question, because the Gorgon was snuffed in the largest mass-murder in history: the Permian extinction of 250 million years ago that killed 95 percent of the species on earth. It was so extraordinary that it makes the Cretaceous extinction - the one that killed the dinosaurs 65 million years ago - look like a decidedly second-rank disaster.

Every schoolchild knows that the dinosaurs were wiped out by a meteor that hit the Yucatan, a theory now so familiar and accepted that it may be hard to recall that just two decades ago the death-by-meteor version of what killed the dinosaurs was nothing more than a brash, new hypothesis.

Ward, a professor of geological sciences at the University of Washington in Seattle, is one of the numerous scientists who spent the 1980s studying the Cretaceous extinction for evidence to confirm or contradict that theory. With the verdict firmly established by 1990, he lit out for South Africa to examine ammonites, creatures with shells rather like a nautilus that became extinct together with the dinosaurs.

There are two stories being told here: the central tale of scientific quest, and a secondary account of South Africa seen through the time-lapse lens of a scientist who makes a series of lengthy visits during the transition from apartheid. The more exciting of the two is the quest to discover what killed the Gorgon and the myriad species that died with them.

When Ward began his field work in South Africa, the cause of the Permian extinction was unknown but the timing was considered well understood: Unlike the dinosaur's sudden-death-by-meteor, the Permian extinction was a gradual process stretching over millions of years.

When border fighting made his collection area unsafe for examining ammonite-bearing strata, Ward decided to tag along with geologist Roger Smith on a trip to examine Permian strata in the Karoo desert. It would be one of those apparent setbacks that later sparks inspiration. By the time the two geologists headed back to Capetown, they were intrigued by the possibility that the Permian extinction was a sudden event, not a gradual process.

Close examination of the strata led Ward and Smith to believe that something had rapidly changed a settled landscape in which a broad river meandered through mature forests into a raw, young landscape like that found at the base of a glacier, where braided rivers crisscross barren, rocky soil. Such a change, presumably caused by a massive tectonic event in which a range of mountains suddenly rose and rapidly began to crumble, would alter the vegetation and result in mass extinction.

But over pizza in a tiny desert town on a bone- chilling winter night, they asked each other, what if it happened the other way around? What if something caused a mature forest to suddenly die, the way the mature forests on the slope of Mt. St. Helen suddenly died.

The result would be a mass of debris that would swiftly replace a broad, meandering river with a series of braided streams traversing raw, rocky land. You have only to stand at a Park Service overlook on the slope of Mt. St. Helen and compare a 1980 photograph with the scene spread at your feet to be persuaded that this kind of thing can happen with stunning rapidity.

But a scientific hunch, however well-founded, is very far from a defensible hypothesis. The fun in Ward's book comes from watching as he and colleagues devise ways of establishing the time-sequence of the Permian extinction and discover what really killed the ferocious Gorgon.

• Diana Muir is the author of 'Reflections in Bullough's Pond: Economy and Ecosystem in New England' (University Press of New England).