Witness the sheer size of the crater as compared to Paris! (headline pic) via Outerplaces: Scientists have discovered a crater beneath Greenland's Hiawatha Glacier that they say could be one of the 25 largest impact structures on Earth. It's a 31-kilometre-wide circular bedrock depression up to a kilometre below the ice and was likely caused by a fractionated iron asteroid about a kilometre wide. Its impact would have had substantial environmental consequences in the Northern Hemisphere and perhaps even more widely, say the researchers, led by led by Kurt Kjær from the University of Copenhagen, Denmark. The crater is the only one of its size that retains a significant portion of its original surface topography. The researchers are unsure of its exact age, but suggest it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet, more than two million years ago. Using dating techniques, they inferred that the young ice covering the crater is "well behaved" but that