Sceince of dating events using ice

Though not as cataclysmic as the dinosaur-killing Chicxulub impact, which carved out a 200-kilometer-wide crater in Mexico about 66 million years ago, the Hiawatha impactor, too, may have left an imprint on the planet's history.

The timing is still up for debate, but some researchers on the discovery team believe the asteroid struck at a crucial moment: roughly 13,000 years ago, just as the world was thawing from the last ice age.

The news of the impact discovery has reawakened an old debate among scientists who study ancient climate.

A massive impact on the ice sheet would have sent meltwater pouring into the Atlantic Ocean—potentially disrupting the conveyor belt of ocean currents and causing temperatures to plunge, especially in the Northern Hemisphere.

The resulting explosion packed the energy of 700 1-megaton nuclear bombs, and even an observer hundreds of kilometers away would have experienced a buffeting shock wave, a monstrous thunder-clap, and hurricane-force winds.

Later, rock debris might have rained down on North America and Europe, and the released steam, a greenhouse gas, could have locally warmed Greenland, melting even more ice.

But the idea caught the public's imagination despite an obvious limitation: No one could find an impact crater."What would it mean for species or life at the time?It's a huge open question," says Jennifer Marlon, a paleoclimatologist at Yale University.A white fireball four times larger and three times brighter than the sun would have streaked across the sky.If the object struck an ice sheet, it would have tunneled through to the bedrock, vaporizing water and stone alike in a flash.

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