Washington: Tiny particles of diamond dust that exist in sediments dating back to 12,900 years indicates earth's impact with a rare swarm of carbon-and-water-rich comets or carbonaceous chondrites.
These nanodiamonds, produced under high-temperature, high-pressure conditions during cosmic impacts and found in meteorites, are concentrated in six northern American sites across US and Canada.
Nanodiamonds can be produced on Earth, but only through high-explosive detonations or chemical vaporisation.
Last year a 26-member team from 16 institutions proposed that a cosmic impact event, possibly by multiple airbursts of comets, set off a 1,300-year-long cold spell known as the Younger Dryas, fragmented the prehistoric Clovis culture and led to the extinction of a large range of animals, including mammoths, across North America.
A team led by University of Oregon's Douglas J. Kennett reports finding billions of nanometre-sized diamonds concentrated in sediments - about 10 to 2,700 parts per billion - in the six locations during digs funded by the National Science Foundation.
"These discoveries provide strong evidence for a cosmic impact event at approximately 12,900 years ago that would have had enormous environmental consequences for plants, animals and humans across North America," said Kennett.
The Clovis culture of hunters and gatherers was named after hunting tools referred to as Clovis points, first discovered in a mammoth's skeleton in 1926 near Clovis, New Mexico. Clovis sites were later identified across the United States, Mexico and Central America, said a Oregon release.
Clovis people possibly entered North America across a land bridge from Siberia. The peak of the Clovis era is generally considered to have run from 13,200 to 12,900 years ago. One of the diamond-rich sediment layers reported sits directly on top of Clovis materials at the Murray Springs site.
These findings appeared in Friday's issue of Science.
