低硫酸塩と無酸素の証拠は,プロテロゾイク中期の海洋盆地にある
Yanan Shen1, Andrew H Knoll, Malcolm R Walter
1Botanical Museum, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA. yshen@oeb.harvard.edu
Nature
|June 6, 2003
まとめ
地球 地球 地球 地球 地球 地球
科学分野:
- 地質化学 地質化学
- パレオセアノグラフィー
- 進化生物学の進化生物学について
背景:
- 地球は,2つの主要な酸素化イベントを経験しました: 2,400 2,200 百万年前と 800 580 百万年前.
- これらの出来事は,プロテロゾーイク時代の海は,無酸化アルカイアンと酸化ファネロゾーイク時代の海とは異なる独特の化学反応を持っていたことを示唆している.
- プロテロゾイク時代の海洋リドックス化学を理解することは,進化論の研究に不可欠ですが,経験的データは限られています.
研究 の 目的:
- プロテロゾイク中期 (約1,500~1,400億年前) の海洋化学を調査する.
- プロテロゾイク時代の海洋環境のモデルに経験的制約を与える.
- ローパー盆地 (オーストラリア) のシェイルの鉄と硫黄の同位体を分析するために.
主な方法:
- ローパー盆地からのシェールにおける鉄の化学分析.
- シェール内のピライトにおける硫黄同位体組成の調査.
- 地化学データと古深層グラデーションの相関.
主要な成果:
- シェイルは,酸化した地表水と共存する深水無酸素を示しています.
- 硫黄の同位体変異は,プロテロゾーイク期中期の海洋における低硫酸塩濃度を示している.
- 証拠は,プロテロゾーイク時代に,長生きした,中間的な海洋化学状態があったことを支持しています.
結論:
- プロテロゾイク中期の海洋は,完全に無酸素でも完全に酸素でもなく,中間的な酸化還元状態を維持していた.
- この状態は,初期の酸素化によって確立され,プロテロゾイク期末期の環境変化で終わった.
- 発見は,初期の生命の進化に影響を及ぼしたユニークな海洋化学の長い期間を支持しています.
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