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Baptistina's Terrible Daughters

Some 250 million years ago, a biological catastrophe struck Earth. An estimated 75 percent of all land-living species and up to 95 percent of all ocean-dwelling species disappeared forever in a geologically brief pulse of mass extinction. And it probably occurred in less than 160,000 years--perhaps as little as 10,000 years. That is equivalent to less than a second if Earths entire history were compressed into a single day.

The mass extinction at the end of the Permian geological period was the worst such event Earth has ever endured. It was far worse than the better-known extinction 65 million years ago that ended the dinosaur era. Imagine that 99 out of every 100 people you know suddenly died. Now imagine that entire families of animals, not just individual species, suddenly disappeared: no more rabbits, no more bats, no more horses. The Great Dying, as some call the end-Permian extinction, was the biggest population crash in evolutionary history.

Scientists have long struggled to understand what virtually transformed Earth into a cemetery. The scenarios proposed so far include a global decline in sea-water oxygen levels, greenhouse warming, and massive volcanic eruptions. Evidence has recently emerged for an entirely different kind of disaster that may have contributed to the Permian mass die off: a strike by a 30-mile-wide (50 kilometers) asteroid.

In 2006, Ohio State University geoscientist Ralph von Frese reported possible evidence of a geologic structure resembling an impact crater. The feature is buried in rock miles beneath the East Antarctic ice sheet. It lies below a region called Wilkes Land and may be more than 300 miles wide (500 km). If the feature is found" to be an impact crater--and the evidence is very far from conclusive--it would be large enough to swallow Ohio.

Von Frese has no direct, physical evidence to prove the Antarctic feature is a crater. Nor does he have geological proof that it even dates to the end-Permian time. The...