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The Morokweng crater (or Morokweng impact structure) is an impact crater buried beneath the Kalahari Desert near the town of Morokweng in South Africa's North West province, close to the border with Botswana. The crater, formed by an asteroid in diameter, is at least about in diameter and the age is estimated to be 145.0 ± 0.8 million years, placing it at the Jurassic–Cretaceous boundary. Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and gravimetric surveys. Core samples have shown it to have been formed by the impact of an L chondrite asteroid. In May, 2006, a group of scientists drilling into the site announced the discovery of a -diameter fragment of the original asteroid at a depth of below the surface, along with several much smaller pieces a few millimetres across at other depths. This discovery was unexpected, since previous drillings on large impact craters had not produced such fragments, and it was thought that the asteroid had been almost entirely vaporised. Some of the fragments can be seen in the Antenna Wing of London's Science Museum. ==References== * * 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「Morokweng crater」の詳細全文を読む スポンサード リンク
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