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By David Freeman
An international team of researchers says they have discovered a large scale impact crater hiding under more than half a kilometer of ice in Greenland.
More than 19 miles wide and about 1000 feet deep, the huge bowl-shaped depression is larger than Washington, DC and one of the 25 largest craters ever discovered on Earth. It is also the first crater discovered under a continental ice floe.
The crater was formed when a meteorite more than a kilometer wide crushed into an area now covered by the Hiawatha Glacier, in northwestern Greenland, announced the researchers in an article describing their discovery.
Researchers can not determine the age of the crater. Kurt Kjaer, a professor at the Geogenetics Center of the Natural History Museum, said, however, that its well-preserved form suggests that it "formed" after the ice began to cover Greenland less than three years ago. millions of years and maybe only 12,000 years ago ". Denmark in Copenhagen and the leader of the team, said in a written statement.
Whatever the age of the crater, his discovery reminds us that Earth still has some secrets in its pocket.
"We still have a lot to understand about our landscape," said Joe MacGregor, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the science team. "This is especially true in the polar regions because ice covers a large part of the surface".
The researchers first discovered crater tracks in 2015, noticing an unusual feature on a topographic map made from data obtained from a NASA aircraft that had inspected the area with radar penetrating the ice. They spent the next three years confirming the discovery, using additional satellite imagery and aerial surveys using a newer and more sophisticated radar system.
"The ice sheet radar survey is a decades old technology, but the system we used to study the Hiawatha Glacier is the most sophisticated ever to monitor a glacier," MacGregor told NBC News MACH. in an email.
In their last step to confirm the discovery, scientists visited the region in 2016 and 2017 to collect samples of sediments that had been washed away by the glacier. The samples included quartz pieces with internal structures that were deformed by intense pressure.
This so – called shocked quartz was found in other impact craters as well as in areas where underground nuclear tests were conducted. His presence helped convince the researchers that the strange feature of the map was really an impact crater.
Other scientists want more evidence.
"I can say that what they present as shocking quartz is certainly shocking quartz," Ludovic Ferriere, an expert in impact craters at the Natural History Museum in Vienna, told National Geographic. "I think they have something here," he added, "but they draw solid conclusions based on very preliminary data."
Clark Chapman, a retired global scientist at the Southwest Research Institute in Boulder, Colorado, expressed similar skepticism. He stated in an email that it was "plausible that the feature is an impact crater", but it was hard to know because the terrain is buried so deep under the ice and can not be reached directly.
In response to criticism, MacGregor said the researchers hoped to return to the area for additional research, while recognizing the difficulty of drilling through the ice and underlying bedrock for more evidence. It would be a difficult process that could take several years, he said.
But he stated that the existing evidence was sufficient and that, given the shape of the geological feature under the ice and sediment samples collected nearby, there was only a "very minimal" chance that the feature under the ice is not an impact crater.
"The simplest explanation of our observations is that the glacier covers an impact crater," he said.
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