Mass extinction
About 13,000 years ago, more than three-fourths of the large Ice Age animals, including woolly mammoths, mastodons, saber-toothed tigers and giant bears, died out. Scientists have debated for years over the cause of the extinction, with both of the major hypotheses — human overhunting and climate change — insufficient to account for the mega die-off.
Recent research suggests that an extraterrestrial object, possibly a comet, about 3 miles wide, may have exploded over southern Canada, nearly wiping out an ancient Stone Age culture as well as megafauna like mastodons and mammoths.