地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
論説
古生代末(2.5億年前)大量絶滅層準の高いヘリウム同位体記録
─冥王代以来の地球史を通した地球外物質流入同定方法の探索─
高畑 直人尾上 哲治佐野 有司磯﨑 行雄
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ジャーナル フリー

2019 年 128 巻 4 号 p. 667-679

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 It is important to know the influx of extraterrestrial material on old Earth in order to understand global environmental changes. Helium is suitable for detecting extraterrestrial material in marine sediments, as well as platinum group elements, because there is more helium in extraterrestrial matter than on the Earth's surface. Extraterrestrial material is detected in old sedimentary rocks collected from a Permian/Triassic (P/T) boundary section in the Mino Belt, central Japan, which accumulated in a deep seafloor environment in the ancient Pacific Ocean. Much higher 3He/4He ratios (up to 150 Ra; 1 Ra = the atmospheric ratio) are observed in the samples. These high 3He/4He ratios may infer the existence of extraterrestrial helium carried in fullerenes or interplanetary dust particles. Moreover, the distribution of 3He concentrations indicates a significant increase in the influx of extraterrestrial material before the P/T boundary, which is equivalent to the influx at the Cretaceous/Paleogene boundary, because of the long duration. This increase may have caused global cooling leading to mass extinction.

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© 2019 公益社団法人 東京地学協会
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