66 million years ago an asteroid longer than Mount Everest is tall hurtled toward the Earth crashing into the Gulf of Mexico. More than 75% of plant and animal species, including the dinosaurs, vanished. it took over 4 million years for life to flourish once again, but the environment was altered forever. So scientists were shocked when they discovered another large impact crater, buried a kilometer under Greenland’s Hiawatha glacier. What was even more shocking was the crater’s lack of erosion, which suggests that the asteroid could have made impact when humans were roaming the earth. To be certain that their find was really an impact crater, researchers used ice penetrating radar to get a sense of the shape of the bedrock underneath the ice. The radar revealed one tell-tale characteristic: a raised area in the center, where the ground would have rebounded after the asteroid hit, like water struck by a stone. Further evidence came from the sediment draining out of the glacier itself. Shocked quartz grains were discovered, which could only be formed by extraterrestrial strikes or nuclear weapons. It was, indeed, an impact crater. 31 kilometers in diameter that makes it one of the 25 largest known craters in the world, though it is smaller than the asteroid impact that killed the dinosaurs, and the Chesapeake Bay crater. The asteroid making the Hiawatha crater would have needed to be enormous too, with a diameter of more than 1.5 kilometers. Scientists still aren’t sure how young Hiawatha is, but it is new enough that it is the only crater of its size still visible to the naked eye– at least, if you could see through the ice. Evidence suggests it is between a 100,000 to 12,000 years old, though it could also be millions of years older. If the impact happened when Greenland was covered in ice, which is most of the past two million years, billions of tons of ice would have vaporized in an instant, leading to an influx of fresh water into the world’s oceans. Just such an influx may have happened about 12,800 years ago, helping to set off a thousand-year glacial period called the Younger Dryas. But evidence for such a flood remains inconclusive. When the asteroid did hit, faraway regions would have felt the impact. Hurricane-force winds would have engulfed the region and objects as far away as a hundred kilometers would have been leveled. The next step is pinning down precisely when this massive asteroid arrived. And then the search can begin for other craters lurking beneath the ice.