Hagstrum and his colleagues suggest that the abundance of these microspherules indicates that the animals died as a result of airbursts or impacts from astronomical objects. Some of these explosive events may have been on the scale of the 1908 Tunguska event, in which a foreign object between 200 and 620 feet in diameter exploded over Siberia, knocking down some 80 million trees in a blast roughly equal to the Castle Bravo thermonuclear explosion.

“Primary blast injuries are caused by the nearly instantaneous change in environmental pressure from passage of the blast wave,” the researchers write. “Blast winds from the impacts would have swept across the Beringian landscape flattening trees and killing, dismembering, and burying megafaunal carcasses or body parts, along with logs, branches, other plant material, with a matrix of redeposited loess in low-lying creek valleys.”

The current findings play in to the Younger Dryas impact hypothesis, which states that cosmic impacts, not humans, may have caused most of North America’s large animals to go extinct during the Late Pleistocene. This hypothesis is widely contested, however, and many scientists contendthere’s no good evidence for it, instead favoring the idea that humans hunted megafauna to extinction. The impact hypothesis also suffers from a conspiracy problem. Oddball thinkers like Graham Hancock have co-opted it to write than impacts during the Younger Dryas doomed the lost civilization of Atlantis, which pretty much all available evidence suggests existed purely in the realm of fiction.

The present paper lends credence to the Younger Dryas impact hypothesis, but the sample size of fossils is minuscule. Moreover, classification of microspherules can be very subjective and open to interpretation. As the authors admit, “further studies of fossils with well-established stratigraphic contexts are needed before the actual role of impacts in driving or contributing to the megafaunal extinctions can be inferred.”

Source: Jonathan T. Hagstrum, Richard B. Firestone, Allen West, James C. Weaver & Ted E. Bunch. Impact-related microspherules in Late Pleistocene Alaskan and Yukon “muck” deposits signify recurrent episodes of catastrophic emplacement. Scientific Reports 7, Article number: 16620 (2017) doi:10.1038/s41598-017-16958-2