Evidence for an extraterrestrial impact 12,900 years ago thatcontributed to megafaunal extinctions and the Younger Dryas cooling
A carbon-rich black layer, dating to ~;12.9 ka, has beenpreviously identified at ~;50 Clovis-age sites across North America andappears contemporaneous with the abrupt onset of Younger Dryas (YD)cooling. The in situ bones of extinct Pleistocene megafauna and Clovistool assemblages occur below this black layer but not within or above it.Causes for the extinctions, the YD cooling, and the termination of Clovisculture have long been controversial. In this paper, we provide evidencefor an extraterrestrial (ET) impact event at ?12.9 ka, which, wehypothesize, caused abrupt environmental changes that contributed to YDcooling, major ecological reorganization, broad-scale extinctions, andrapid human behavioral shifts at the end of the Clovis Period. Clovis-agesites in North American are overlain by a thin, discrete layer withvarying peak abundances of: (1) magnetic grains with iridium, (2)magnetic microspherules (3) charcoal, (4) soot, (5) carbon spherules, (6)glass-like carbon, and (7) fullerenes with ET helium, all of which areevidence for an ET impact and associated biomass burning at ~;12.9 ka.This layer also extends throughout at least fifteen Carolina Bays, whichare unique, elliptical wetlands, oriented to thenorthwest across theAtlantic Coastal Plain. We propose that one or more large, low-density ETobjects exploded over northern North America, partially destabilizing theLaurentide Ice Sheet and triggering YD cooling. The shock wave, thermalpulse, and event-related environmental effects (e.g., extensive biomassburning, food limitations) contributed to the end-Pleistocene megafaunalextinctions and adaptive shifts among PaleoAmericans in NorthAmerica.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director, Office of Science; National ScienceFoundation
- DOE Contract Number:
- DE-AC02-05CH11231; NSF:9986999, OCD-0244201, ANDATM-0713769
- OSTI ID:
- 928884
- Report Number(s):
- LBNL-63274; R&D Project: NISON; BnR: KB0301042; TRN: US0803275
- Journal Information:
- Proceedings of the National Academy ofSciences, Vol. 104, Issue 41; Related Information: Journal Publication Date: 08/09/2007
- Country of Publication:
- United States
- Language:
- English
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