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Woodleigh is a large meteorite impact crater (astrobleme) in Western Australia, centred on Woodleigh Station east of Shark Bay. A team of four scientists at the Geological Survey of Western Australia and the Australian National University, led by Arthur J. Mory, announced the discovery in the 15 April 2000 issue of ''Earth and Planetary Science Letters''.〔 (Abstract )〕 The crater is not exposed at the surface and therefore its size is uncertain. The original discovery team believe it may be up to in diameter,〔 but others argue it may be much smaller, with one study suggesting a diameter closer to .〔 (Abstract and full PDF )〕 The larger estimate of 120 km, if correct, would make this crater tied for the fourth largest confirmed impact structure in the world, and imply a bolide (asteroid or comet) about in diameter.〔 (PDF )〕 A more recent study suggests the crater could be between 60 to 160 km or more, and was produced by a comet or asteroid 6 to 12 km wide. The central uplift, interpreted to be in diameter, was first intersected by drilling activities in the late 1970s; however its significance as an impact structure was only realised in 1997 during a gravity survey.〔 In 1999 a new core sample was taken. The thin veins of melted glass, breccia, and shocked quartz found would have formed under pressures 100,000 times greater than atmospheric pressure at sea level, or between 10 and 100 times greater than those generated by volcanic or earthquake activity. Only a large impact could have generated such conditions. The Woodleigh impact event, originally thought to have occurred between the Late Triassic and Late Permian, is now thought to date from 364 ± 8 million years (Late Devonian). This time corresponds approximately to a minor extinction event when around 40% of species disappeared. There is evidence for other large impact events at around the same time, so if the extinction is related to impact, perhaps more than one crater was involved. Of the two dozen or more impact craters known in Australia, the three largest are Woodleigh, Acraman, and Tookoonooka.〔 ==Notes== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Woodleigh crater」の詳細全文を読む スポンサード リンク
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