Great Balls of Fire

It occurred in a blink of an eye--geologically speaking--about 250 million years ago. In the space of a few thousand years, something terrible happened to our planet, something that wiped out 90% of Earth's ocean species and about 70% of those that lived on land.

It was the worst extinction in the history of the earth; scientists call it the Great Dying. It eliminated whole communities of coral reefs, forests of fernlike trees, giant amphibians and ferocious reptiles, swarms of seemingly indestructible insects and the ocean's ubiquitous trilobites, those hard-shelled invertebrates with complex eyes that were never seen on the planet again.

What caused the so-called Permian extinction? Any number of scenarios have been offered, ranging from the explosion of a nearby star to Ice Age cooling and greenhouse warming. None of them were entirely convincing.

Last week a team led by a junior professor from the University of Washington appeared to have finally cracked the puzzle. Writing in the journal Science, Luann Becker and her colleagues blame "this mother of all extinctions," as she calls it, on the impact of an asteroid or comet like the one that probably wiped out the dinosaurs 65 million years ago. In each case the damage would have been done not by the explosive collision itself but by the series of global disasters it triggered: furious volcanic eruptions, a rapid heating of the atmosphere and the depletion of life-giving oxygen from the ocean.

On what evidence do Becker and her colleagues base their conclusion? Tiny smoking guns in the form of soccer-ball-shaped carbon molecules called buckminsterfullerenes, or buckyballs (after Buckminster Fuller, inventor of the geodesic dome). In sites ranging from Hungary to China and Japan, scientists digging in layers of 250-million-year-old rock found scattered buckyballs that had trapped in their cagelike structure traces of extraterrestrial gases--helium and argon in a rare form that scientists know could have been forged only during star formation.

The scientists can't say exactly where the comet or asteroid struck because the tectonic processes that rearrange the earth's surface have since churned up most of the evidence. But they can estimate its size. It probably measured 4 to 7 miles across--roughly half the size of the island of Manhattan--and it would have slammed into the earth with the force of a magnitude-12 earthquake.