Geoscientists haven’t found a lot of surprise craters on Earth since satellite technology became commonplace. Still, the complex geological processes on this blue marble can occasionally conceal a secret. Several years ago, scientists discovered a crater hiding under Greenland’s ice sheet. At the time, they believed it was between three million and 1,200 years old. Now, we know they missed the mark by millions of years, reports Gizmodo.
The crater managed to avoid detection for so long because it’s completely covered by 1,000 feet of ice. The only hint of its existence is a round projection of the ice sheet (see above), which is what caught the attention of the University of Copenhagen’s Nicolaj Larsen. He discovered the crater by accident while examining maps of the region, announcing the find in 2018. Follow-up observations confirmed there was a crater under there, and it’s no small fry. With a diameter of 19 miles (31 kilometers), this is one of the 25 largest craters on Earth.
At the time of its discovery, the team had good circumstantial evidence to indicate the crater was younger. The crater appeared to have minimal erosion, and the strata contained disturbed ice from the last ice age and organic remains from forests that covered Greenland until a few million years ago. This seemed to jive with what we know about this period in history, known as the Younger Dryas. To know for sure, they needed a sample from the crater basin. Easy… except for the ice sheet covering the crater.
Instead of digging through a thousand feet of ice, the team visited areas around the ice sheet in search of materials from the crater. After three seasons of hunting, the team found melted sand and shocked zircon crystals that were carried downstream by meltwater. Researchers dated both materials and got the same result: the impact happened 58 million years ago, just a few million years after the Cretaceous–Paleogene extinction.
While the impact does not coincide with the Younger Dryas, there should be some environmental mark. The object was about 0.6 miles (1 kilometer) in diameter, which could have thrown up enough material to alter the climate. However, it’s unlikely this impact would have caused anything approaching a mass extinction. Researchers will now be on the lookout for geological evidence of such an event.
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from ExtremeTechExtremeTech https://ift.tt/KidCMw4
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