约会大气中氧气的增加
A Bekker1, H D Holland, P-L Wang
1Department of Earth and Planetary Sciences, 20 Oxford Street, Harvard University, Cambridge, Massachusetts 02138, USA. abekker@fas.harvard.edu
Nature
|January 9, 2004
概括
大气中氧气的增加发生在232亿年前,硫同位素在铁矿和铁矿形成中证明了这一点. 这一发现完善了我们对早期地球的理解.
科学领域:
- 地质化学 地质化学
- 古气候学 古气候学
- 早期地球的地质学
背景情况:
- 以前的地质和地化学数据表明,在245亿年前之前,大气中的氧气含量很低,在222亿年前的显著水平.
- 大氧化事件的时间仍然是理解早期地球大气演变的关键问题.
研究的目的:
- 为确定大气氧气增加的时间提供新的证据.
- 为了研究南非Rooihoogte和Timeball Hill形成的沉积环境.
主要方法:
- 在有机丰富的页岩中分析合成矿的硫同位素成分.
- 在研究的地质单位内检查铁构成,包括 sideritic 卵石和 hematitic pisolites/oölites.
- 解释硫同位素数据以证明质量独立分化 (MIF) 的证据及其对大气氧气水平的影响.
主要成果:
- 有着广泛的硫同位素,缺乏质量独立分离的合成矿在232亿年前的页岩中被发现.
- 这表明在页岩沉积过程中存在大量大气氧气 (大于当前大气水平的10-5倍).
- 存在的 sideritic 铁形成卵石和厚厚的铁石层进一步支持大气中的氧气在这些构成沉积期间显著上升.
结论:
- 大气氧气的增加发生在232亿年前,比之前估计的时间框架更早.
- 这些发现表明,这种氧化事件可能与古新生代冰川事件相吻合.
- 这项研究完善了大氧化事件的时间表及其与早期地球主要气候变化的潜在联系.
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