Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
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Communicated by Steven M. Stanley, University of Hawaii, Honolulu, HI, June 11, 2009 (received for review March 3, 2009)
Abstract
The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (Mammuthus exilis) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at ≈12,900 ± 100 cal BP.
Footnotes
- 1To whom correspondence should be addressed. E-mail: dkennett{at}uoregon.edu
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Author contributions: D.J.K., J.P.K., T.E.B., J.M.E., S.S.Q.H., F.S., and W.S.W. designed research; D.J.K., J.P.K., A.W., G.J.W., T.E.B., B.J.C., J.M.E., J.R.J., C.M., F.S., M.S., A.S., J.C.W., J.H.W., and W.S.W. performed research; S.S.Q.H. and W.S.W. contributed new reagents/analytic tools; D.J.K., J.P.K., A.W., G.J.W., T.E.B., J.M.E., C.M., F.S., T.W.S., J.C.W., J.H.W., and W.S.W. analyzed data; and D.J.K. and J.P.K. wrote the paper.
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The authors declare no conflict of interest.
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↵* Ages in this paper are expressed in thousands of calendar years before present (ka). Radiocarbon ages will be identified and clearly marked “14C years.”
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This article contains supporting information online at www.pnas.org/cgi/content/full/0906374106/DCSupplemental.
Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments
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