A Significantly High He Isotopic Signature from the End-Paleozoic (250 Ma) Extinction-related Interval: For Detecting Ancient Extraterrestrial Fluxes through the Earth's History since the Hadean

Abstract

 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.