Meteor impact might have led to dawn of civilization
Washington: Dartmouth researchers have for the first time, linked a cataclysmic meteor impact in Canada to the start of civilisation.
Evidence indicates an asteroid or comet struck Quebec around 12,900 years ago.
Scientists believe the impact caused a transition to a colder, drier climate around the world which had far-reaching effects.
In North America, the big animals all vanished, including mastodons, camels, giant ground sloths and saber-toothed cats.
Their human hunters, known to archaeologists 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 impacted human history in a profound manner," Dartmouth Professor Mukul Sharma, a co-author of the study, said.
"Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture," he said.
It is not disputed that these powerful environmental changes occurred, but there has long been controversy over their cause.
The classic view of the Younger Dryas cooling interlude has been that an ice dam in the North American ice sheet ruptured, releasing a massive quantity of freshwater into the Atlantic Ocean. The sudden influx is thought to have shut down the ocean currents that move tropical water northward, resulting in the cold, dry climate of the Younger Dryas.
But Sharma and his co-authors have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation.
The report focuses on spherules, or droplets of solidified molten rock expelled by the impact of a comet or meteor.
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 argue the impact took place.
The findings are published online in Early Edition of the Proceedings of the National Academy of Sciences.
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