There's been a lot of talk about an extraterrestrial impact in North America about 11,000 years ago. The idea is that such an event could have contributed to the extinction of North America's megafauna, like giant ground sloths and wooly mammoths. A new paper in PNAS by Haynes et al [LINK] examine the evidence from several "Clovis" sites. These are sites where remains of the Clovis people [wikipedia] have been found. Their analysis finds no strong evidence of an extraterrestrial impactor, and especially damning to me is that they find no enhancement of Iridium, which is a fingerprint for impacts.
While they are careful to say that they haven't ruled out an impact, I think this is strong evidence that the other hypotheses (e.g., human hunting) are more likely to have led to the megafaunal extinction.