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Did a humongous space rock smash into Canada 12,900 years ago?

Tiny spherules in Quebec suggest a massive meteor impact, one that may have helped usher in a new ice age, say scientists. But other scientists disagree.

By Becky OskinLivescience.com / September 3, 2013

The high temperatures of the meteorite impact 12,900 years ago produced mm-sized spherules of melted glass with the mullite and corundum crystal structure shown here.

Mukul Sharma

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A meteor or comet impact near Quebec heaved a rain of hot melted rock along North America's Atlantic Coast about 12,900 years ago, a new study claims.

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Scientists have traced the geochemical signature of the BB-sized spherules that rained down back to their source, the 1.5-billion-year-old Quebecia terrane in northeastern Canada near the Gulf of Saint Lawrence. At the time of the impact, the region was covered by a continental ice sheet, like Antarctica and Greenland are today.

"We have provided evidence for an impact on top of the ice sheet," said study co-author Mukul Sharma, a geochemist at Dartmouth College in Hanover, N.H. The results were published today (Sept. 2) in the journal Proceedings of the National Academy of Sciences.

Younger Dryas?

The new research shakes up a controversial theory about a big climate shift called the Younger Dryas, when Earth abruptly swung into a glacial period 12,900 years ago. The cooling has been attributed to a sudden shutdown in Northern Atlantic Ocean currents, caused by a big glacial lake flood out the St. Lawrence or Mackenzie Rivers. But in 2007, scientists suggested that comet or meteor impacts or atmospheric fireballs triggered the Younger Dryas, though no crater of the right age has ever been found.

The tiny particles from New Jersey and Pennsylvania, analyzed by Sharma and his colleagues, have never been accurately dated, Sharma admits. They could be several thousands years older than the widespread glacial event. "We are assuming they are Younger Dryas, but [dating] is one of the things that should be done better," Sharma told LiveScience.

And geochemical tracers in the molten rock show it can't be traced back to a recently discovered impact crater near Quebec called Corossal crater, thought to be Younger Dryas-age. [When Space Attacks: The 6 Craziest Meteor Impacts]

The researchers also proved that spherules from sites in North America and Europe, thought to be evidence of Younger Dryas comet impacts, didn't come from outer space. Sharma and his colleagues measured osmium isotopes in the melted rock and their surrounding sediment. Meteorites usually carry much more osmium than Earth rocks. (Isotopes are versions of elements with different numbers of neutrons.) But none of the spherules were extraterrestrial, Sharma said.

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