古代ジルコンの酸素同位体の証拠は,4,300万年前に地球の表面で液体の水が存在していたことを示しています
S J Mojzsis1, T M Harrison, R T Pidgeon
1Department of Earth and Space Sciences and IGPP Center for Astrobiology, University of California Los Angeles, 90095-1567, USA. Steve.Mojzsis@lasp.colorado.edu
Nature
|February 24, 2001
まとめ
西オーストラリアの古代ジルコンは,初期の地球には地表水があったことを示唆しています. この43億年前の鉱物残骸は,惑星の形成段階で大陸の地殻と相互作用する水球の存在を示しています.
科学分野:
- 地質学 地質学 地質学
- 地質化学 地質化学
- 惑星科学は惑星科学である.
背景:
- 最も古い大陸の地殻の露出は38億~40億年前のものです.
- 初期の地球の表面条件を理解するには,40億年以上前の岩石や鉱物の残骸を分析する必要があります.
研究 の 目的:
- 40億年以上前の地球表面の条件を調査する.
- 古代のジルコンの源の年代と組成を制限するために.
- 初期の地球の表面の性質についての洞察を提供するために.
主な方法:
- In situ Uranium-Lead (U-Pb) によるジルコンのデトリタル年代測定.
- デトリタルジルコンの酸素同位体分析 (デルタ18O)
- 西オーストラリアの30億年前の石英岩の中に発見されたジルコンの分析.
主要な成果:
- 年代付けされたジルコンは3910~4280万年前のもの.
- 酸素同位体値 (デルタ18O) は5.4±0.6%から15.0±0.4%に変化した.
- およそ4億3千万年前のジルコンは,大陸の地殻を大幅に改造したマグマから形成された可能性が高い.
結論:
- 地球表面近くの水の存在は,古代ジルコンの同位体組成によって示されています.
- これらの発見は,水球が430億年前に地殻と相互作用していたことを支持しています.
- この研究は,早期の地殻の進化と,原始的な地球に表面水の存在の証拠を提供します.
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