A giant meteorite crater has been found lurking beneath the Greenland ice sheet – and the impact might explain a puzzling mini ice age about 13,000 years ago called the Younger Dryas.
The crater – a round bowl-shaped depression about 30 kilometres wide – was discovered from old NASA radar data. It would have been made by a meteorite about 1 kilometre in diameter – a tenth the size of the asteroid that killed off the dinosaurs 66 million years ago.
Although the crater is completely covered by a region of ice called the Hiawatha Glacier, a subsurface river draining from underneath is leaving tell-tale sediment on the exposed land between the ice and the sea.
Some of the sediment particles have an internal structure that shows they were subjected to a short-lived high-pressure shock wave, says Iain McDonald of Cardiff University. “They’re absolutely characteristic of impact.”
They even hint at the composition of the meteorite. They contain metals such as gold, nickel and cobalt, indicating the space object was a relatively rare iron meteorite. These originate from the metal cores inside planetoids, formed early in the history of the Solar System.
Without access to the crater, the team haven’t yet been able to date the event more precisely than some time in the past three million years. But that leaves open the possibility the meteorite could be connected to the Younger Dryas, says McDonald.
The cause of this short episode of Northern Hemisphere cooling that started abruptly during a longer period of warming has long been unclear. There are several theories, including an impact from space, but there was no suitable crater recent enough.
If the Greenland meteorite had hit ice several hundred metres thick, as it is over Greenland now, it would have melted millions of tonnes of fresh water, which would have entered the sea. This could have disrupted ocean circulatory currents, and cooled the climate, McDonald speculates. “Circumstantially, the fact that we have found a crater hidden under ice opens up this possibility.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.aar8173
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