In the journal Science Advances, researchers make the case that a meteorite perhaps a mile wide slammed into Greenland somewhere between 12,000 and 3 million years ago, reports the Guardian. After spotting the indentation in the radar images, the researchers set about getting samples to confirm their hunch.
"Some of the quartz sand coming from the crater had planar deformation features indicative of a violent impact; this is conclusive evidence that the depression beneath the Hiawatha Glacier is a meteorite crater", said Larsen, one of the study's co-authors, in a statement.
The study's abstract says: "The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet".
After receiving a new map of bedrock topography under the ice, thanks to two decades' worth of NASA's expeditions in the area, scientists began to look closer at a "conspicuously semi-circular" section of the ice sheet's edge. They had also used Alfred Wegener Institute's powerful ice-penetrating radar system that was operated from the air back in 2016 to determine the concrete place of the crater.
"The crater is exceptionally well-preserved, and that is surprising, because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact", Professor Kurt H Kjær said. "We suspect these initially detached in Earth's gravity field and then decelerated as they entered the atmosphere to fall south of the Hiawatha crater".
The crater was identified with data collected between 1997 and 2014 by NASA's Program for Arctic Regional Climate Assessment and Operation IceBridge, and supplemented with more data collected in May 2016 using the Multichannel Coherent Radar Depth Sounder.
Cardiff University in the United Kingdom, which was also involved in the study, said the dramatic impact "could have drastically altered the climate and led to serious consequences for life on Earth at the time".
Accurately dating the collision will provide future research with a better understanding of the consequences of such an impact and how it affected the environment on the Earth.
"The next step in the investigation will be to confidently date the impact".