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

The Murray Springs Clovis site, Pleistocene extinction, and the question of
extraterrestrial impact

    1. C. Vance Haynes Jr.^a,^1,
    2. J. Boerner^b,
    3. K. Domanik^c,
    4. D. Lauretta^c,
    5. J. Ballenger^d, and
    6. J. Goreva^c

    1. 


    ^aSchool of Anthropology and Department of Geosciences,University of
    Arizona, PO Box 210030, Tucson, AZ 85721
    2. 


    ^bDepartment of Geosciences, University of Arizona, PO Box 210077,
    Tucson, AZ 85721
    3. 


    ^cLunar and Planetary Laboratory, Department of Planetary Sciences,
    University of Arizona, PO Box 210092, Tucson, AZ 87521
    4. 


    ^dSchool of Anthropology, University of Arizona, PO Box 210030,
    Tucson, AZ 85721

    1. Edited by George C. Frison, University of Wyoming, Laramie, WY,
       and approved December 8, 2009 (received for review July 29, 2009)

Abstract

   Some of the evidence for the recent hypothesis of an extraterrestrial
   impact that caused late Pleistocene megafaunal extinctions [Firestone
   et al. (2007) Proc Natl Acad Sci USA 104:16016-16021] was based upon
   samples collected at Murray Springs, a Clovis archaeological site in
   southeastern Arizona. Here we describe sampling and analyses of
   magnetic separates from within, above, and below the lower Younger
   Dryas boundary (LYDB) black mat at Murray Springs, as well as
   radiation measurements from the LYDB at Murray Springs and two other
   well-stratified Clovis sites. The main magnetic fraction at Murray
   Springs is maghemite. Magnetic microspherules have terrestrial origins
   but also occur as cosmic dust particles. We failed to find iridium or
   radiation anomalies. The evidence for massive biomass burning at
   Murray Springs is addressed and found to be lacking. We could not
   substantiate some of the claims by Firestone and others, but our
   findings do not preclude a terminal Pleistocene cosmic event.