Rock & Gem

Re-dating an Impact Crater Beneath the Ice of Greenland


Using ice-penetratin­g radar, in 2018 earth and planetary scientists including Kurt Kjaer (Natural History Museum of Denmark) discovered an impact crater nearly 20 miles wide beneath the vast glacial ice sheets of northwest Greenland. ‰ey attributed it to an asteroid that could have been as large as a mile in diameter. But, lacking direct geological samples of rocks, they were never sure just how old it was. ‰at led to all sorts of speculatio­n. For instance, some thought a huge meteor strike 10,000 to 100,000 years ago could have initiated the so-called Younger Dryas cooling period that may have caused the extinction of some Ice Age mammals.

But now it appears the crater is far, far older. Just how old? A recent re-evaluation of evidence puts it at 58 million years old. ‰at’s well before the Ice Ages and not so very long a•fter the dinosaurs went extinct 66 million years ago.

It was believed to be impossible to directly date the crater given that it’s covered by more than 2,600 feet of ice. But the same team that made the initial discovery has examined minerals, including zircon, in “shocked rocks” that have spilled out from streams ˜owing beneath the Hiawatha Glacier covering the impact crater. Per their new analysis, described in the journal Science Advances, this evidence shows a very ancient date, indeed. Some are now suggesting that the impact creating this crater may have been responsibl­e for initiating a period of intense global warming during the Eocene Epoch. ‰us, a whole new period of speculatio­n has just been unleashed by a crater still hidden far from reach.

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