EU scientists find Earth's oldest crater in Greenland
European scientists have found a 100 kilometre-wide crater in Greenland, the result of a massive asteroid or comet impact a billion years before any other known collision on Earth. Only around 180 impact craters have ever been discovered on Earth, but finding them can reveal hidden treasures - around 30% of them contain important natural resources of minerals or oil and gas, explained the international team led by Adam A. Garde, a senior research scientist at the Geological Survey of Denmark and Greenland (GEUS) in Copenhagen. The findings have just been published in the journal Earth and Planetary Science Letters. The spectacular craters on the moon formed from impacts with asteroids and comets between 3 and 4 billion years ago. The early Earth, with its far greater gravitational mass, must have experienced even more collisions at this time - but the evidence has been eroded away or covered by younger rocks. '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 astronomically low,' explained the researchers. But they - a team of scientists from GEUS, Cardiff University in Wales, Lund University in Sweden and the Institute of Planetary Science in Moscow - have upset these odds. Following a detailed programme of fieldwork, funded by GEUS and the Danish 'Carlsbergfondet' (Carlsberg Foundation), the team discovered the remains of a giant 3 billion year old impact near the Maniitsoq region of West Greenland. The largest and oldest known crater prior to this study, the 300 km-wide Vredefort crater in South Africa, is 2 billion years in age and heavily eroded. Dr Iain McDonald from Cardiff University's School of Earth and Ocean Sciences, who was part of the team, explained that it had not been easy to persuade the scientific community of the importance of such research, but insisted that industry was clear about the potential benefits of finding new craters. 'It has taken us nearly three years to convince our peers in the scientific community of this but the mining industry was far more receptive,' he said. 'A Canadian exploration company has been using the impact model to explore for deposits of nickel and platinum metals at Maniitsoq since the autumn of 2011.' Dr McDonald said that in addition to the potential mineral deposits, this research is important as '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'. The team highlighted the difficulties associated with the research. 'Finding the evidence was made all the harder because there is no obvious bowl-shaped crater left to find,' said the scientists. They explained how 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,' explained 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.'For more information, please visit:Cardiff University:http://www.cardiff.ac.uk
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