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thumb Tswaing is an impact crater in South Africa. It is situated 40 km to the north-west of Pretoria. This astrobleme is 1.13 km in diameter and 100 m deep and the age is estimated to be 220,000 ± 52,000 years (Pleistocene).〔(【引用サイトリンク】title=Tswaing and its environmental effects )〕 The impactor is believed to have been a chondrite or stony meteorite some 30 to 50 m in diameter that was vaporized during the impact event.〔 Morokweng crater, another crater of chondrite origin, lies north-west of Vryburg. The name ''Tswaing'' means ''Place of Salt'' in Tswana and the crater was also formerly known in (英語:as Pretoria Saltpan crater) and in (アフリカーンス語:as Soutpankrater). Stone tools from the Middle Stone Age show that the crater was regularly visited by people from as far back as 100,000 years ago in order to hunt and collect salt. Water in the crater comes from surface springs, ground water and rain water and is rich in dissolved carbonates and sodium chlorides. Tswana and Sotho people harvested the salt by filtering and decoction between 1200 and 1800. Between 1912 and 1956 brine was pumped from the floor of the crater by the company ''SA Alkali Ltd.'' in order to extract soda and salt.〔Tswaing information leaflet〕 A scientific dispute was ongoing regarding the origin of the crater between supporters of volcanic origin (Wagner, 1922) and those who believed it is an impact crater (Rohleder, 1933) until 1990, when examination of the core from a borehole proved that it is an impact crater.〔(【引用サイトリンク】title=Tswaing crater )〕 Tswaing is currently on the ''tentative list'' for consideration as a World Heritage Site. ==See also== * Impact event * List of impact craters in Africa 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「Tswaing crater」の詳細全文を読む スポンサード リンク
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