硫黄のイソトープは,アルカイア時代の有酸素大気の証拠である
Hiroshi Ohmoto1, Yumiko Watanabe, Hiroaki Ikemi
1NASA Astrobiology Institute and Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. ohmoto@geosc.psu.edu
Nature
|August 25, 2006
まとめ
質量独立硫黄同位体 (MIF-S) は,古代オーストラリアの岩石には存在せず,初期の酸素化された大気という考えに異議を唱えている. この発見は,MIF-Sの起源は,大気化学のみに依存しないかもしれないことを示唆しています.
科学分野:
- 地質化学 地質化学
- 同位体地質学とは,同位体地質学である.
- パレオ大気は,パレオ大気である.
背景:
- 24億年以上前の岩石における硫黄同位体 (MIF-S) の質量独立分離は,無毒大気を示すと考えられていた.
- 若い岩石におけるMIF-Sの欠如は,硫黄二酸化物のUV光分解に起因する酸化大気への移行を支えた.
研究 の 目的:
- 古代の堆積岩におけるMIF-Sの存在と起源を調査する.
- 古代時代のMIF-Sと大気中の酸素レベルとの関係を再評価する.
主な方法:
- 2.76-Gyr-old湖の堆積物の約100mのセクションで硫黄の同位体の分析. 2.76-Gyr-old湖の堆積物.
- 西オーストラリアのピルバラ・クレートン (Pilbara Craton) の2.92Gyr古い海洋シェールにおける硫黄同位体の分析.
主要な成果:
- MIF-Sの欠如は,古代の湖の堆積物と海洋シェールの両方で検出されました.
- この発見は,以前のモデルに基づいた,この年齢の岩石におけるMIF-Sの予想される存在と対照的です.
結論:
- MIF-Sの地質学的な記録は,再解釈を必要とするかもしれません.
- 可能性のある説明には,変動するアーカイア時代の酸素レベル,MIF-Sに影響を与える火山活動,または大気化学とは無関係にMIF-Sを生成する非光化学的ダイアゲネティックプロセスが含まれます.
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