The Younger Dryas impact hypothesis: review of the impact evidence

Firestone et al., 2007, PNAS 104(41): 16016-16021, proposed that a major cosmic impact, circa 10,835 cal. BCE, triggered the Younger Dryas (YD) climate shift along with changes in human cultures and megafaunal extinctions. Fourteen years after this initial work the overwhelming consensus of research undertaken by many independent groups, reviewed here, suggests their claims of a major cosmic impact at this time should be accepted. Evidence is mainly in the form of geochemical signals at what is known as the YD boundary found across at least four continents, especially North America and Greenland, such as excess platinum, quench-melted materials, and nanodiamonds. Their other claims are not yet confirmed, but the scale of the event, including extensive wildfires, and its very close timing with the onset of dramatic YD cooling suggest they are plausible and should be researched further. Notably, arguments by a small cohort of researchers against their claims of a major impact are, in general, poorly constructed, and under close scrutiny most of their evidence can actually be interpreted as supporting the impact hypothesis.