(July 21, 2009)
A 17-member team has found what may be the smoking gun of a much-debated proposal that a cosmic impact about 12,900 years ago ripped through North America and drove multiple species into extinction.
In a paper appearing online
ahead of regular publication in the Proceedings
of the National Academy of Sciences,
These tiny diamonds and diamond
clusters were buried deeply below four meters of sediment. They date to the end
The diamonds were found in association with soot, which forms in extremely hot fires, and they suggest associated regional wildfires, based on nearby environmental records.
Such soot and diamonds are rare in the geological record. They were found in sediment dating to massive asteroid impacts 65 million years ago in a layer widely known as the K-T Boundary. The thin layer of iridium-and-quartz-rich sediment dates to the transition of the Cretaceous and Tertiary periods, which mark the end of the Mesozoic Era and the beginning of the Cenozoic Era.
"The type of diamond we have found -- Lonsdaleite -- is a shock-synthesized mineral defined by its hexagonal crystalline structure. It forms under very high temperatures and pressures consistent with a cosmic impact," Kennett said. "These diamonds have only been found thus far in meteorites and impact craters on Earth and appear to be the strongest indicator yet of a significant cosmic impact [during Clovis]."
The age of this event also
matches the extinction of the pygmy mammoth on the
In the Jan. 2, 2009, issue of the journal Science, a team led by Kennett reported the discovery of billions of nanometer-sized diamonds concentrated in sediments -- weighing from about 10 to 2,700 parts per billion -- in six North American locations.
"This site, this layer with
hexagonal diamonds, is also associated with other types of diamonds and with
dramatic environmental changes and wildfires," said James Kennett,
paleoceanographer and professor emeritus in the Department of Earth Science at
"There was a major event 12,900 years ago," he said. "It is hard to explain this assemblage of materials without a cosmic impact event and associated extensive wildfires. This hypothesis fits with the abrupt cooling of the atmosphere as shown in the record of ocean drilling of the Santa Barbara Channel. The cooling resulted when dust from the high-pressure, high-temperature, multiple impacts was lofted into the atmosphere, causing a dramatic drop in solar radiation."
The hexagonal diamonds from
Transmission electron microscopy and scanning electron microscopes were used in the extensive analyses of the sediment that contained clusters of Lonsdaleite ranging in size from 20 to 1,800 nanometers. These diamonds were inside or attached to carbon particles found in the sediments.
These findings are inconsistent
with the alternative and already hotly debated theory that overhunting by
The National Science Foundation
provided primary funding for the research. Additional funding was provided by
way of Richard A. Bray and Philip H. Knight faculty fellowships of the
The 17 co-authors on the PNAS paper are Douglas Kennett, Erlandson and Brendan J. Culleton, all of the University of Oregon; James P. Kennett of UC Santa Barbara; Allen West of GeoScience Consulting in Arizona; G. James West of the University of California, Davis; Ted E. Bunch and James H. Wittke, both of Northern Arizona University; Shane S. Que Hee of the University of California, Los Angeles; John R. Johnson of the Santa Barbara Museum of Natural History; Chris Mercer of the Santa Barbara Museum of Natural History and National Institute of Materials Science in Japan; Feng Shen of the FEI Co.; Thomas W. Stafford of Stafford Research Inc. of Colorado; Adrienne Stich and Wendy S. Wolbach, both of DePaul University in Chicago; and James C. Weaver of the University of California, Riverside.
Alternate Media Contact: Gail Gallessich, science writer, UC Santa Barbara, 805-893-7220, .edu
Sources: Douglas Kennett,
professor of archaeology, department of anthropology, .edu. He currently is in
James Kennett, professor emeritus, UC Santa Barbara, 805-893-4187, .edu (home phone number for media access is available from either media contact above)
Links: Doug Kennett faculty page: http://www.uoregon.edu/~dkennett/Welcome.html; anthropology department: http://www.uoregon.edu/~anthro/
James Kennett faculty page: http://www.geol.ucsb.edu/faculty/kennett/Home.html
Adapted from materials provided by University of Oregon.