Massive impact crater beneath Greenland could explain Ice Age climate swing

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12,800 years ago, during the Pleistocene, Earth was warming up from its last Ice Age. Temperatures slowly rose while glaciers retreated, that is, until something major happened that triggered a cold snap big enough to leave its mark on the geologic record. Over the course of just decades – the blink of an eye in geological timescales – the planet cooled somewhere between 3 and 11 degrees Fahrenheit (2 to 6 degrees Celsius). The resulting period is known as the Younger Dryas, a mysterious 1000-year blip in history.

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The work, led by Kurt Kjær, professor at the Natural History Museum of Denmark and University of Copenhagen, describes a previously overlooked, 19-mile-wide crater that’s been hiding in plain sight in northwest Greenland’s Hiawatha Glacier. In fact, it’s only about 150 miles from Thule Air Base – the U.S.’s northernmost Air Force base and the place where NASA’s IceBridge planes took flight. You can see about a third of the crater’s rounded outline on Google Earth.