大规模的 siderite 床的证据表明,大约在 18 亿年前之前,有一个富含 CO2 的大气层
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
概括
早期的地球地球.
科学领域:
- 地质化学 地质化学
- 古气候学 古气候学
- 早期的地球研究研究.
背景情况:
- 早期地球可能需要温室气体来维持液态海洋,因为太阳的流量较低.
- 在22亿年前之前,甲被假设为一个关键的温室气体.
- 这种假设是基于古石中缺少 siderite,这表明大气中的二氧化碳含量较低.
研究的目的:
- 重新评估甲和二氧化碳在维持早期地球液态海洋中的作用.
- 研究大气组成的地质约束.
主要方法:
- 多维热力学分析.
- 考察地质证据,特别是古岩和富含 siderite 的床.
- 在沉积物序列中分析碳同位素比率.
主要成果:
- 古中缺少 siderite 并不能可靠地限制大气中的二氧化碳水平.
- 赛德里特的形成取决于土壤的氧气和pH值,在空气良好的土壤中有利于铁矿物质.
- 在整个地质历史中, siderite 始终在地下,无氧环境中形成.
- 在18亿年前的序列中,大量的 siderite 床显示大气中二氧化碳含量显著增加 (> 100 倍于当前水平).
结论:
- 仅仅是二氧化碳,没有显著的甲,可以为早期地球的液态海洋提供足够的温室效应.
- 早期地球大气中的二氧化碳含量远远高于以前从古石中 siderite 的缺失中推断出来的.
- 高度的二氧化碳可能导致了早期地球上更多的酸性雨和海洋水.
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