Lawrence Berkeley National Laboratory
The Case for the Younger Dryas Extraterrestrial Impact Event: Mammoth, Megafauna and Clovis Extinction
- Author(s): Firestone, Richard B
- et al.
The onset of >1000 years of Younger Dryas cooling, broad-scale extinctions, and the disappearance of the Clovis culture in North America simultaneously occurred 12,900 years ago followed immediately by the appearance of a carbon-rich black layer at many locations. In situ bones of extinct megafauna and Clovis tools occur only beneath this black layer and not within or above it. At the base of the black mat at 9 Clovis-age sites in North America and a site in Belgium numerous extraterrestrial impact markers were found including magnetic grains highly enriched in iridium, magnetic microspherules, vesicular carbon spherules enriched in cubic, hexagonal, and n-type nanodiamonds, glass-like carbon containing Fullerenes and nanodiamonds, charcoal, soot, and polycyclic aromatic hydrocarbons. The same impact markers were found mixed throughout the sediments of 15 Carolina Bays, elliptical depressions along the Atlantic coast, whose parallel major axes point towards either the Great Lakes or Hudson Bay. The magnetic grains and spherules have an unusual Fe/Ti composition similar to lunar Procellarum KREEP Terrane and the organic constituents are enriched in 14C leading to radiocarbon dates often well into the future. These characteristics are inconsistent with known meteorites and suggest that the impact was by a previous unobserved, possibly extrasolar body. The concentration of impact markers peaks near the Great Lakes and their unusually high water content suggests that a 4.6 km-wide comet fragmented and exploded over the Laurentide Ice Sheet creating numerous craters that now persist at the bottom of the Great Lakes. The coincidence of this impact, the onset of Younger Dryas cooling, extinction of the megafauna, and the appearance of a black mat strongly suggests that all these events are directly related. These results have unleashed an avalanche of controversy which I will address in this paper.