Honolulu, HI, July 26, 2007 (received for review March 13, 2007)
A carbon-rich black layer, dating to {approx}12.9 ka, has been
previously identified at {approx}50 Clovis-age sites across North
America and appears contemporaneous with the abrupt onset of
Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene
megafauna, along with Clovis tool assemblages, occur below this
black layer but not within or above it. Causes for the extinctions,
YD cooling, and termination of Clovis culture have long been
controversial. In this paper, we provide evidence for an
extraterrestrial (ET) impact event at {cong}12.9 ka, which we
hypothesize caused abrupt environmental changes that contributed to
YD cooling, major ecological reorganization, broad-scale
extinctions, and rapid human behavioral shifts at the end of the
Clovis Period. Clovis-age sites in North American are overlain by a
thin, discrete layer with varying peak abundances of (i) magnetic
grains with iridium, (ii) magnetic microspherules, (iii) charcoal,
(iv) soot, (v) carbon spherules, (vi) glass-like carbon containing
nanodiamonds, and (vii) fullerenes with ET helium, all of which are
evidence for an ET impact and associated biomass burning at
{approx}12.9 ka. This layer also extends throughout at least 15
Carolina Bays, which are unique, elliptical depressions, oriented to
the northwest across the Atlantic Coastal Plain. We propose that one
or more large, low-density ET objects exploded over northern North
America, partially destabilizing the Laurentide Ice Sheet and
triggering YD cooling. The shock wave, thermal pulse, and
event-related environmental effects (e.g., extensive biomass burning
and food limitations) contributed to end-Pleistocene megafaunal
extinctions and adaptive shifts among PaleoAmericans in North
America.
Full PDF Report Here
No comments:
Post a Comment