Illustration by Chris Foss/NGS
Diamond dust found in 12,900-year-old sediments at six North American sites boosts evidence of Earth’s impact with a swarm of comets at that time, researchers reported today.
The discovery supports the theory that an impact with an extraterrestrial object may have contributed to the disappearance of large mammals and the Clovis culture of prehistoric humans, the scientists say.
Scientists proposed in 2007 that a cosmic impact, 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.
Illustration of woolly mammoth by Charles R. Knight/NGS
In today’s issue of the journal Science, a team led by the University of Oregon’s Douglas J. Kennett, a member of the 2007 research team, reports finding billions of microscopic-size diamonds in sediments in the six locations (see map below) during digs funded by the National Science Foundation.
“The nanodiamonds that we found at all six locations exist only in sediments associated with the Younger Dryas Boundary layers, not above it or below it,” said Kennett, a University of Oregon archaeologist, in a university press release.
Kennett and colleagues say the only obvious explanation for the concentration of nanodiamonds (seen in the image on the left) is that they were created in the high-energy environment of an impact by a comet or other extraterrestrial object.
“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.”
The comet-impact theory of the cause of the Younger Dryas has met with skepticism. Other theories for what triggered the global cooling event include a sudden drainage of a vast inland lake from North America into the ocean, disrupting the ocean current system and causing the continent to cool.
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 later were identified across the United States, Mexico and Central America.
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, according to the UO news release. “One of the diamond-rich sediment layers reported sits directly on top of Clovis materials at the Murray Springs site” in Arizona.
Photo of Clovis point by David Arnold/NGS
Map showing distribution of nanodiamonds in Younger Dryas sediments across North America courtesy University of Oregon.