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   PNAS
   Proceedings of the National Academy of Sciences of the United States
   of America

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

    1. Douglas J. Kennett^a,^1,
    2. James P. Kennett^b,
    3. Allen West^c,
    4. G. James West^d,
    5. Ted E. Bunch^e,
    6. Brendan J. Culleton^a,
    7. Jon M. Erlandson^a,^f,
    8. Shane S. Que Hee^g,
    9. John R. Johnson^h,
   10. Chris Mercer^i,^j,
   11. Feng Shen^k,
   12. Marilee Sellers^e,
   13. Thomas W. Stafford, Jr^l,
   14. Adrienne Stich^m,
   15. James C. Weaver^n,
   16. James H. Wittke^e and
   17. Wendy S. Wolbach^m

    1. 


    ^aDepartment of Anthropology and
    2. 


    ^fMuseum of Natural and Cultural History, University of Oregon,
    Eugene, OR 97403;
    3. 


    ^bDepartment of Earth Science and Marine Science Institute and
    4. 


    ^jMaterials Department, University of California, Santa Barbara, CA
    93106;
    5. 


    ^cGeoScience Consulting, Dewey, AZ 86327;
    6. 


    ^dDepartment of Anthropology, University of California, Davis, CA
    95616;
    7. 


    ^eDepartment of Geology and Imaging and Histology Core Facility,
    Northern Arizona University, Flagstaff, AZ 86011;
    8. 


    ^gDepartment of Environmental Health Sciences, University of
    California, Los Angeles, CA 90095-1772;
    9. 


    ^hSanta Barbara Museum of Natural History, 2559 Puesta del Sol,
    Santa Barbara, CA 93105;
   10. 


    ^iNational Institute for Materials Science, Tsukuba, Ibaraki
    305-0047, Japan;
   11. 


    ^kFEI Company, 5350 Northeast Dawson Creek Drive, Hillsboro, OR
    97124;
   12. 


    ^lStafford Research, Inc., 200 Acadia Avenue, Lafayette, CO 80026;
   13. 


    ^mDepartment of Chemistry, DePaul University, Chicago, IL 60604; and
   14. 


    ^nDepartment of Chemical and Environmental Engineering, University
    of California, Riverside, CA 92521

    1. 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.
     * Arlington Canyon
     * biomass burning
     * cosmic impact
     * hexagonal nanodiamonds
     * megafaunal extinctions

Footnotes

     * ^1To whom correspondence should be addressed. E-mail:
       dkennett{at}uoregon.edu
     * 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.
     * The authors declare no conflict of interest.
     * RET* Ages in this paper are expressed in thousands of calendar
       years before present (ka). Radiocarbon ages will be identified and
       clearly marked "^14C years."
     * This article contains supporting information online at
       www.pnas.org/cgi/content/full/0906374106/DCSupplemental.

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