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Science 2 January 2009:
Vol. 323. no. 5910, p. 94
DOI: 10.1126/science.1162819
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Brevia

Nanodiamonds in the Younger Dryas Boundary Sediment Layer

D. J. Kennett,1* J. P. Kennett,2 A. West,3 C. Mercer,4 S. S. Que Hee,5 L. Bement,6 T. E. Bunch,7 M. Sellers,7 W. S. Wolbach8

We report abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earth's typical surficial processes but common to cosmic impacts. N-diamond concentrations range from {asymp}10 to 3700 parts per billion by weight, comparable to amounts found in known impact layers. These diamonds provide strong evidence for Earth's collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.

1 Department of Anthropology, University of Oregon, Eugene, OR 97403, USA.
2 Department of Earth Science, University of California, Santa Barbara, CA 93106, USA.
3 GeoScience Consulting, Dewey, AZ 86327, USA.
4 National Institute for Materials Science, Tsukuba 305-0047, Japan.
5 Department of Environmental Health Sciences/Center for Occupational and Environmental Health, University of California, Los Angeles, CA 90095–1772, USA.
6 Oklahoma Archeological Survey, University of Oklahoma, Norman, OK 73019, USA.
7 Departments of Geology and Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA.
8 Department of Chemistry, DePaul University, Chicago, IL 60614, USA.

* To whom correspondence should be addressed. E-mail: dkennett{at}uoregon.edu

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