For the first time, a dramatic climate shift that has long fascinated scientists has been linked to the impact in Quebec, Canada of an asteroid or comet by Dartmouth College researchers and their colleagues.
The event took place about 12,900 years ago, at the beginning of the Younger Dryas period, and marks an abrupt global change to a colder, dryer climate, with far-reaching effects on both animals and humans, the scientists say.
In North America the big animals, including mastodons, camels, giant ground sloths, and saber-toothed cats, all vanished, researchers said.
Their human hunters, known as the Clovis people, set aside their heavy-duty spears and turned to a hunter-gatherer subsistence diet of roots, berries, and smaller game.
"The Younger Dryas cooling is a very intriguing event that impacted human history in a profound manner," said Mukul Sharma, a professor in the Department of Earth Sciences and one of the authors of the study.
"Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture," said Sharma.
That these powerful environmental changes occurred is not in dispute, but there has been controversy over why they happened.
The classical view of the Younger Dryas cooling interlude has been that a surge of meltwater from the North American ice sheet was behind it all.
However, Sharma and his colleagues have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation.
The report focuses on spherules, droplets of solidified molten rock expelled by the impact.
The spherules in question were recovered from Younger Dryas boundary layers at sites in Pennsylvania and New Jersey, the layers having been deposited at the beginning of the period.
The geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma and his colleagues say the impact took place.
"What is exciting in our paper is that we have for the first time narrowed down the region where a Younger Dryas impact did take place, even though we have not yet found its crater," said Sharma.
The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).