PP41A-03: The End Pleistocene Extinction Event - What Caused It?
It is well established that the last catastrophic faunal extinction in the geologic past coincided with the end of the
Pleistocene during the deglaciation between the last glacial episode and the present Holocene interglacial. The
cause of this extinction has been debated for many years but remains highly controversial in part because of
limitations of available data, but also because the two major hypotheses that have been long invoked, climate
change and human overhunting, have continued to present significant problems. Recently, Firestone et al. [1]
have reported strong evidence for an extraterrestrial (ET) impact including peak abundances of metallic
microspherules and magnetic grains with elevated iridium, glass-like carbon, carbon microspherules, soot and
charcoal in a carbon-rich black layer dating close to ~12.9 ka (referred to as Younger Dryas Black Layer or YDB) in
numerous terminal Clovis-age sites across North America. To assess the YDB impact hypothesis and its
potential effects on the megafauna and humans in North America [2-4], we have analyzed several well-dated
suites of samples in search of fullerenes with ET noble gases and other impact debris (e.g. microspherules).
These sites include Daisy Cave (DC) on California's San Miguel Island, Murray Springs (MS) in Arizona and
Blackwater Draw (BWD) in New Mexico, all well known previously described archaeological and paleontological
sites, with established chronologies spanning the YDB (~12.9 k) [5-7]. To further assess the environmental
effects of the impact on the Pleistocene fauna and human activity, we examined the YDB layer at each of these
locations for evidence of wildfires triggered by the ET event. If there were wildfires, a group of high molecular
weight aromatic compounds or polycyclic aromatic hydrocarbons (PAHs) should be present in the associated
soot and charcoal material within the YDB. By examining the distributions of the PAHs, the source of these
compounds, wildfire or human activity, can be determined. The recognition of global wildfires at the time of the K/T
impact event was first proposed based on the presence of elemental carbon (mainly soot) associated with ET
tracers in the boundary layer [8-10]. Soot produced by severe wildfires at the YDB would have severely affected the
ecological niches, reduced primary productivity, eliminated food sources and added to the effects of the ejecta
cloud [8]. Here, we present our evidence in support of an ET impact and its effects on the environment at the YDB
and compare these results to other well-known impact events in the geologic record. [1] Firestone et al. (2006)
Proceeding of the National Academies of Science (submitted). [2] Martin, P.S. Twilight of the Mammoths Ice Age
Extinctions and the Rewilding of America. University of California Press, Berkeley 250 pp. (2005). [3] Haynes, C.V.
(2002) World Archeology 33,391-416. [4] Grayson, D. K. and Meltzer, D.J. (2002) Journal of World Prehistory 16,
313-359. [5] Erlandson, J.M. et al. (1996) Radiocarbon 38,355-373. [6] Haynes, C.V.et al., (1999) Geoarcheology:
An International Journal, 14, 455-470.[7] Tayler, R.E., Haynes, C.V. and Stuvier, M. (1996) Antiquity 70, 515-525. [8]
Wolbach, W.S., Lewis, R.S. and Anders, L.E. (1985) Science 230,167-170. [9] Wolbach et al. (1988) Nature
334,57-669. [10] Venkatesan, M.I. and Dahl, J. (1989) Nature 338,57-60.