A giant comet slammed into the atmosphere and fractured. The resulting swarm of fragments also exploded, scattering tiny diamonds in widely separated locations and plunging the warming Earth into a renewed and deadly deep freeze.

When Leland Bement first heard the theory, "I was highly skeptical," he said. "You just roll your eyes."

But a discovery in the Oklahoma Panhandle changed his viewpoint. It began when Bement, research archaeologist with the Oklahoma Archaeological Survey, was contacted by a team of scientists who had read about Bement's research. For years, Bement had been studying remnants of Indian communities that existed around the end of the last Ice Age - about 13,000 years ago - in the area that is now the Panhandle.

The scientists seeking evidence to bolster their comet theory figured Bement and his colleagues had "exactly the right time period for what we're looking for," Bement said. Bement took the comet researchers to Bull Creek and other locations where bluffs of stratified earth offer an archaeological timeline, the lower layers being from earlier and earlier periods.

Several months later, Bement received results of the team's analysis. By soaking soil samples in acid, the team isolated material as hard as diamond.

By firing X-rays through the remaining material, the comet researchers found what they were looking for, "nanodiamonds" a millionth of a millimeter across, so small 1 billion would be only the size of a sugar cube. Such carbon structures cannot be created by any natural forces on Earth, Bement said. Only the pressures and heat from something like a comet burst could produce them.

The particular sample in which the crystalline dust was found was key. It was from strata representing a geologic period that Bement's research had confirmed was when mammoths disappeared from the area on their way to extinction. Also at that time, 13,000 years ago, the Earth was still warming from an ice age, but the climate abruptly reversed. Within 40 years, the average global temperature had dropped 8 degrees centigrade, suggesting a "nuclear winter" effect created by a comet.
The nanodiamonds also pinpointed when diets of Indian people Bement was studying suddenly changed from mammoth meat to bison and deer. And it was when the Indian "Clovis" culture - marked by specific tools and other artifacts - abruptly disappeared, giving way to the "Folsom" culture.

"Oh man, they just nailed it exactly where it should have been," Bement said.

The findings do not seal the comet theory, however. As with most research, many questions remain, and others are posed by the findings. For instance, Bement said, "How do you kill off the mammoth and not kill off the buffalo?" Also, Bement has found evidence of Clovis groups after the comet period.

It could be that there were just more bison than mammoths, so bison survived and repopulated, he speculated. And perhaps the Folsom shift was a result of technological advances rather than catastrophe.

"All of this is just hypothesis that adds more layers of questions on top of all these questions we had to begin with," Bement said. "It keeps you scratching your head."