A 100 kilometer-wide crater has been found in Greenland, the result of a massive asteroid or comet impact a billion years before any other known collision on Earth. The previously oldest known crater on Earth formed 2 billion years ago and the chances of finding an even older impact were thought to be, literally, astronomically low.
"This single discovery means that we can study the effects of cratering on the Earth nearly a billion years further back in time than was possible before," according to Dr Iain McDonald of Cardiff University's School of Earth and Ocean Sciences, who was part of the team.
Finding the evidence was made all the harder because there is no obvious bowl-shaped crater left to find. Over the 3 billion years since the impact, the land has been eroded down to expose deeper crust 25 km below the original surface. All external parts of the impact structure have been removed, but the effects of the intense impact shock wave penetrated deep into the crust - far deeper than at any other known crater - and these remain visible.
However, because the effects of impact at these depths have never been observed before it has taken nearly three years of painstaking work to assemble all the key evidence. "The process was rather like a Sherlock Holmes story," said Dr McDonald. "We eliminated the impossible in terms of any conventional terrestrial processes, and were left with a giant impact as the only explanation for all of the facts."
Only around 180 impact craters have ever been discovered on Earth and around 30% of them contain important natural resources of minerals or oil and gas. The largest and oldest known crater prior to this study, the 300 kilometre wide Vredefort crater in South Africa, is 2 billion years in age and heavily eroded.
If the past is prelude, there's bound to be a massive collision event from a rogue asteroid at some point in the "near" future unless we successfully intervene.The "Impact Map of the World" above shows most of the 160 impact craters that have been identified since 1950. The bulk of the terrestrial impact craters that were ever formed, however, have been obliterated by eons of geological processes.
For further information about the Maniitsoq structure see: http://www.geus.dk … unction=form Link to the paper in Earth & Planetary Science Letters: http://dx.doi.org/ … .2012.04.026 Journal reference: Earth and Planetary Science Letters
The Daily Galaxy via Cardiff University