A Test for the Extraterrestrial Origin of the Magnetic Spherules/Grains at the Younger Dryas Boundary

Dartmouth College, Hanover NH

Investigators

Abstract

The Younger Dryas (YD) event, which began approximately 12,900 years ago, was a period of abrupt and rapid cooling in the Northern Hemisphere whose primary cause remains unclear. The cooling event is of ~1400 year duration and its onset coincides with abrupt Pleistocene megafaunal extinctions and the disappearance of the Clovis people in North America. The prevalent postulated mechanism has been a temporary shutdown of the thermohaline circulation following the breakup of an ice dam in North America. However, a recent paper proposes that the cooling was triggered by multiple cometary airbursts and/or impacts that engendered enormous environmental changes. The evidence in support of this hypothesis is a black layer marking the Younger Dryas boundary in sediments from North America and Europe. This boundary is enriched in magnetic grains high in iridium, magnetic microspherules, nanodiamonds, and fullerenes containing extra-terrestrial He-3. The impact hypothesis is being intensely debated for while the YD horizon shows evidence of extensive forest fires, it lacks traditional impact markers. Moreover, the origin of the magnetic spherules and iridium bearing magnetic grains remains unclear. It is yet to be demonstrated conclusively if these magnetic grains are meteorite debris or micrometeorites or just terrestrial grains singed in a forest fire. The purpose of this pilot study is to test the impact hypothesis by examining the osmium (Os) isotopic composition and osmium and iridium concentrations in magnetic objects separated from the appropriate sections at Gainey (Michigan), Murray Springs (Arizona) and Lommel (Belgium). Additionally, they will also look for evidence of meteorite debris in high resolution sediment cores from Crystal and Mastodon Lakes in Illinois.