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.

A decade ago, a small group of scientists proposed a similar scenario.

The helicopter landed near the surging river that drains the glacier, sweeping out rocks from beneath it.

Kjær had 18 hours to find the mineral crystals that would confirm his suspicions.

Its official chemical symbol is Mg, and its atomic number is 12, which means that magnesium has 12 protons in it ...

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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.It advances on the Arctic Ocean not in a straight wall, but in a conspicuous semicircle, as though spilling out of a basin.Kjær, a geologist at the Natural History Museum of Denmark in Copenhagen, suspected the glacier was hiding an explosive secret.On a bright July day 2 years ago, Kurt Kjær was in a helicopter flying over northwest Greenland—an expanse of ice, sheer white and sparkling.Soon, his target came into view: Hiawatha Glacier, a slow-moving sheet of ice more than a kilometer thick."What would it mean for species or life at the time?