Diamond-rich soil evidences climate change theory

Abundant tiny particles of diamond dust exist in sediments dating to 12,900 years ago at six North American sites, adding strong evidence for Earth's impact with a rare swarm of carbon-and-water-rich comets or carbonaceous chondrites, reports a nine-member scientific team.

These nanodiamonds, which are produced under high-temperature, high-pressure conditions created by cosmic impacts and have been found in meteorites, are concentrated in similarly aged sediments at Murray Springs, Ariz., Bull Creek, Okla., Gainey, Mich., and Topper, S.C., as well as Lake Hind, Manitoba, and Chobot, Alberta, in Canada. Nanodiamonds can be produced on Earth, but only through high-explosive detonations or chemical vaporization.

In 2008, 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. The team's paper was published in the Oct. 9, 2007, issue of the Proceedings of the National Academy of Sciences.

in the PNAS paper, the researchers proposed that a known reversal in the world's ocean currents and associated rapid global cooling, which some scientists blame for the extinction of multiple species of animals and the end of the Clovis Period, was itself the result of a bigger event. While generally accepted theory says glacial melting from the North American interior caused the shift in currents, the new proposal points to a large extraterrestrial object exploding above or even into the Laurentide ice sheet north of the Great Lakes.

At one time this ice sheet covered North America east of the Rocky Mountains, from the Arctic Ocean to a line passing through a region that now encompasses the Dakotas and the cities of New York, Cincinnati, St. Louis and Kansas City. By 13,000 years ago, the ice sheet's southern reach had retreated to what is now Canada.

"Highest concentrations of extraterrestrial impact materials occur in the Great Lakes area and spread out from there," Kennett said. "It would have had major effects on humans. Immediate effects would have been to the north and east (of the impact site), producing shockwaves, heat, flooding, wildfires, and a reduction and fragmentation of the human population."

Led by the University of Oregon's Douglas J. Kennett, a member of the original research team, report finding billions of nanometer-sized diamonds concentrated in sediments -- weighing from about 10 to 2,700 parts per billion -- in the six locations 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 UO archaeologist. "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 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, N.M. 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. One of the diamond-rich sediment layers reported sits directly on top of Clovis materials at the Murray Springs site. 

The eight co-authors on the Science paper were: Douglas J. Kennett's father, James P. Kennett of the University of California, Santa Barbara; A. West of GeoScience Consulting in Dewey, Ariz.; C. Mercer of the National Institute for Materials Science in Tsukuba, Japan; Que Hee of the University of California, Los Angeles; L. Bement of the Oklahoma Archaeological Survey at the University of Oklahoma; T.E. Bunch and M. Sellers, both of Northern Arizona University; and W.S. Wolbach of DePaul University in Chicago.

Info: University of Oregon