The fad for blaming all mass extinctions (such as happened at the end of the Cretaceous when the dinosaurs vanished) on impacts of objects from space was extended to the Pleistocene in 2007. That year a group of scientists proposed that the North American extinctions were due to a comet or meteorite impact over the Carolinas, near the beginning of the Younger Dryas event, about 12,900 years ago. The original evidence for this supposed impact was a "black mat" of organic material in many Clovis sites, plus microscopic nano-diamonds in deep-sea cores, and rare Platinum group metals in Greenland ice cores from around 12,900 years ago.
dcterms:bibliographicCitation
2016 November 15, Donald R. Prothero, The Princeton Field Guide to Prehistoric Mammals‎https://www.google.co.uk/books/edition/The_Princeton_Field_Guide_to_Prehistoric/eiftDAAAQBAJ?hl=en&gbpv=1, page 222: