硫黄同位体から読み取る太古代地球の表層環境 : 現状とその問題点(<特集>アストロバイオロジー)

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概要

• 論文の詳細を見る

• Since the discovery of Anomalous Isotope Fractionation (AIF) of sulfur, or more commonly termed Mass-Independent Fractionation (MIF) of sulfur, in many sedimentary rocks older than 2.45Ga, and its virtual absence in younger rocks, the AIF record has been cited by many researchers as unequivocal evidence for a dramatic change from an anoxic to oxic atmosphere around 2.45Ga. However, multiple sulfur isotope data from these natural samples have been interpreted based on the assumption that sulfur chemistry in gas phase is only responsible for AIF of sulfur in nature. The objective of this review is to evaluate this assumption. First, results of ab initio calculations for equilibrium isotope exchange between S-bearing species show that deviations from the mass-dependent relationships during equilibrium processes are much smaller than those found in Archean sedimentary rocks. Consequently, AIF requires a property that is a discontinuous function of mass (e.g., nuclear volume, magnetic moment, asymmetry of molecules, isotopic abundance). The number of bound states may be another discontinuous function of mass, which fractionates S isotopes anomalously during chemisorption at a high temperature (e.g., >100℃). A recent experimental study also showed that thermochemical sulfate reduction by simple amino acids produces AIF of sulfur. These results suggest that an alternative process, such as reactions between organic matter in sediments and sulfate-rich hydrothermal solutions, may have caused AIF signatures of sulfur in Archean sedimentary rocks.

• 日本地球化学会の論文

著者

• 大竹 翼

  東北大学大学院理学研究科

• 大竹 翼

  東北大・理

• 渡辺 由美子

  The Nasa Astrobiology Institute And Department Of Geosciences The Pennsylvania State University

• 大竹 翼

  東北大学大学院理学研究科地学専攻:(現)産業技術総合研究所地圏資源環境研究部門

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• 硫黄同位体から読み取る太古代地球の表層環境 : 現状とその問題点(アストロバイオロジー)

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