地球上の大規模な硫酸塩堆積物における異常な17O組成
H Bao1, M H Thiemens, J Farquhar
1Department of Chemistry and Biochemistry, University of California San Diego, La Jolla 92093, USA. hbao@chem.ucsd.edu
Nature
|July 26, 2000
まとめ
以前は隕石でしか見られなかった酸素イソトープの質量に依存しない分割は,今や地球の巨大な硫酸塩堆積物で見つかりました. この発見は,大気中の硫黄酸化を追跡し,惑星の同位体異常を理解するのに役立ちます.
科学分野:
- 地質化学 地質化学
- イソトープ地球化学 イソトープ地球化学
- 惑星科学は惑星科学である.
背景:
- 酸素同位体 (デルタ18Oとデルタ17O) は,通常,地上の材料で質量依存分化 (MDF) を示しています.
- 質量独立分化 (MIF) は地球上ではまれで,主に隕石や大気中の物質で観察される.
- 地上の固体は,少なくとも37億年もの間,歴史的にMDFに付着してきました.
研究 の 目的:
- 陸上の大量硫酸塩堆積物における質量独立分化の存在を調査する.
- 観測された酸素同位体異常の潜在的な源と影響を調査する.
- 地球外同位体変異を理解するためのこれらの発見の関連性を評価する.
主な方法:
- 大規模な硫酸塩鉱床における酸素同位体値 (デルタ18Oとデルタ17O) の分析.
- ジプクレット (ナミブ砂漠) とミオセンの火山灰床 (北米) の同位体データ比較.
- 予想される質量依存分割関係からの偏差の評価.
主要な成果:
- 陸上の硫酸塩堆積物における重要な酸素同位体異常 (デルタ17Oでは4.6%まで) の発見.
- これらの異常は,地球の表面環境における質量独立分断を示している.
- この発見は,地上の固体における普遍的なMDFの長期間の仮定に異議を唱える.
結論:
- 地球の大規模な硫酸塩堆積物には,以前から考えられていたこととは対照的に,質量独立した分割法が存在します.
- 観測された異常は,大気中の硫黄酸化反応に起因する可能性がある.
- この研究は,惑星の化学プロセスと,火星のような他の惑星の同位体異常についての洞察を提供します.
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