London, October 13 (ANI): An independent study has cast more doubt on a controversial theory that a comet exploded over icy North America nearly 13,000 years ago, wiping out the Clovis people and many of the continent’s large animals.

In 2007, a team led by Californian researchers announced a theory that a comet or asteroid had exploded over the North American ice sheet, creating widespread fire and an atmospheric soot burst followed by a cooling period known as the Younger Dryas.

Sometime after this, the Clovis people, sophisticated large-animal hunters known for their spear points, mysteriously disappeared.

The team linked their vanishing to the environmental effects of the proposed impact.

Key evidence came in the form of magnetic microspherules discovered in sediments at 25 locations, including eight Clovis-age sites.

Richard Firestone, of Lawrence Berkeley National Laboratory in California, and his colleagues argued that the microspherules were remnants of cosmic debris from an explosion.

But, according to a report in Nature News, in more than 18 months of sedimentary analysis, a team led by Todd Surovell, an archaeologist at the University of Wyoming in Laramie, was unable to detect microspherule peaks.

Two of the seven sites the group studied were places where Firestone’s team identified spherule peaks.

“I spent hundreds of hours at the microscope examining sediment samples and I didn’t find any physical evidence to support their theory,” said Surovell.

Several other groups have been unable to support important aspects of the comet theory.

Jennifer Marlon, a doctoral geography student at the University of Oregon in Eugene, and her colleagues found no systematic burning of biomass - as would have occurred if continent-wide fires had happened - at the time of the Younger Dryas in pollen and charcoal records at 35 sites.

Also, Jacquelyn Gill, a palaeoecology doctoral student at the University of Wisconsin-Madison, reported finding no evidence of massive burning in sediment cores taken from lake beds in Ohio and Indiana. (ANI)