大規模なシデライト岩床から得られた証拠は,約18億年前以前にCO2に富んだ大気が存在していたことを示しています
Hiroshi Ohmoto1, Yumiko Watanabe, Kazumasa Kumazawa
1Astrobiology Research Center of the NASA Astrobiology Institute and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA. ohmoto@geosc.psu.edu
Nature
|May 28, 2004
まとめ
初期の地球 初期の地球
科学分野:
- 地質化学 地質化学
- 古代気候学 (paleoclimatology) とは,古代気候学 (paleoclimatology) とは,古代気候学 (paleoclimatology) とは,古代気候学 (paleoclimatology) とは,古代気候学 (paleoclimatology) とは
- 初期の地球の研究は,初期の地球の研究です.
背景:
- 初期の地球は,太陽の流れが低いため,液体の海洋を維持するために温室効果ガスを必要とした可能性が高い.
- メタンは,22億年前以前に,重要な温室効果ガスであると仮定されています.
- この仮説は,パリオソールにシデライトが存在しないことから,大気中の二酸化炭素が低いことを示唆していた.
研究 の 目的:
- 初期の地球の液体の海洋を維持するメタンと二酸化炭素の役割を再評価する.
- 大気組成に関する地質学的制約を調査する.
主な方法:
- 多次元熱力学分析. 多次元熱力学分析.
- 地質学的証拠の調査,特にパレオソールとシデライトに富んだ床の調査.
- 堆積物の配列における炭素同位体比の分析.
主要な成果:
- パレオソールのシデライトの欠如は,大気中の二酸化炭素レベルを確実に制限することはできません.
- シデライトの形成は,土壌の酸素とpHに依存し,空気量が良い土壌の鉄性鉱物を好む.
- シデライトは地質史を通じて,地表の下の無酸素環境で一貫して形成されています.
- 18億年前以前のシーケンスに豊富に存在するシデライト床は,大気中の二酸化炭素が著しく高かったことを示している (現在のレベルの100倍以上).
結論:
- 大量のメタンを含まない二酸化炭素だけでは,初期の地球の液体海洋に十分な温室効果をもたらすことができた.
- 初期の地球の大気中のCO2レベルは,以前,古生物学におけるシデライトの欠如から推測されたよりも大幅に高かった.
- 高濃度のCO2は,初期の地球でより酸性雨と海洋水の発生につながった可能性が高い.
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