What caused the extinction of mammoths and the decline of Stone Age people about 13,000 years ago remains hotly debated. Overhunting by Paleoindians, climate change and disease lead the list of probable causes. But an idea once considered a little out there is now hitting closer to home.

A team of international researchers, including two Northern Arizona University geologists, reports evidence that a comet or low-density object barreling toward Earth exploded in the upper atmosphere and triggered a devastating swath of destruction that wiped out most of the large animals, their habitat and humans of that period.

“The detonation either fried them or compressed them because of the shock wave,” said Ted Bunch, NAU adjunct professor of geology and former NASA researcher who specializes in impact craters. “It was a mini nuclear winter.”