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

An independent evaluation of the Younger Dryas extraterrestrial impact
hypothesis

    1. Todd A. Surovell^a,^1,
    2. Vance T. Holliday^b,
    3. Joseph A. M. Gingerich^a,
    4. Caroline Ketron^a,
    5. C. Vance Haynes, Jr^b,
    6. Ilene Hilman^a,
    7. Daniel P. Wagner^c,
    8. Eileen Johnson^d and
    9. Philippe Claeys^e

    1. 


    ^aDepartment of Anthropology, University of Wyoming, Laramie, WY
    82070;
    2. 


    ^bDepartments of Anthropology and Geosciences, University of
    Arizona, Tucson, AZ 85721;
    3. 


    ^cGeo-Sci Consultants, Inc., 4410 Van Buren Street, University Park,
    MD 20782;
    4. 


    ^dMuseum of Texas Tech University, Box 43191, Lubbock, TX 79409; and
    5. 


    ^eDepartment of Geology, Vrije Universiteit Brussel, Pleinlaan 2,
    B-1050 Brussels, Belgium

    1. Edited by David Jeffrey Meltzer, Southern Methodist University,
       Dallas, TX, and approved September 3, 2009 (received for review
       July 15, 2009)

Abstract

   Based on elevated concentrations of a set of "impact markers" at the
   onset of the Younger Dryas stadial from sedimentary contexts across
   North America, Firestone, Kennett, West, and others have argued that
   12.9 ka the Earth experienced an impact by an extraterrestrial body,
   an event that had devastating ecological consequences for humans,
   plants, and animals in the New World [Firestone RB, et al. (2007)
   Proc. Natl. Acad. Sci. USA 104:16016-16021]. Herein, we report the
   results of an independent analysis of magnetic minerals and
   microspherules from seven sites of similar age, including two examined
   by Firestone et al. We were unable to reproduce any results of the
   Firestone et al. study and find no support for Younger Dryas
   extraterrestrial impact.
     * Clovis
     * magnetic grains
     * magnetic microspherules
     * Pleistocene extinctions

Footnotes

     * ^1To whom correspondence should be addressed. E-mail:
       surovell{at}uwyo.edu
     * Author contributions: T.A.S. and V.T.H. designed research; T.A.S.,
       V.T.H., J.A.M.G., C.K., C.V.H., I.H., D.P.W., E.J., and P.C.
       performed research; C.V.H., D.P.W., and E.J. contributed new
       reagents/analytic tools; T.A.S., J.A.M.G., and C.K. analyzed data;
       and T.A.S., V.T.H., and J.A.M.G. wrote the paper.
     * The authors declare no conflict of interest.
     * This article is a PNAS Direct Submission.
     * RET^2Firestone et al. (1) examined two types of spherules in their
       study, magnetic microspherules and carbon spherules. In our study,
       we examined only the former.
     * This article contains supporting information online at
       www.pnas.org/cgi/content/full/0907857106/DCSupplemental.