在大氧化事件发生之前,与低初级生产率的古老有机丰富的泥岩进行调和
Noam Lotem1, Birger Rasmussen2, Jian-Wei Zi3
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125.
概括
古代岩石显示有机碳含量高,这并不是由于生产率高,而是由于积累缓慢,在无氧条件下保存良好. 这解决了地球早期生物圈演化的长期悖论.
科学领域:
- 地质化学 地质化学
- 古生物学的古生物学.
- 沉积物学的沉积物学
背景情况:
- 古代泥岩 (>25亿年前) 的高有机碳含量一直是一个难题,因为在氧气上升之前,对于早期的生物圈来说这是意想不到的.
- 之前的研究将这归因于高的生物初级生产率.
研究的目的:
- 研究古代有机丰富的泥岩的积累速度,以解决高有机含量悖论.
- 为了比较古老的沉积设置与Phanerozoic (<5亿年前) 数据.
主要方法:
- 使用U-Pb石从灰床中老化,评估了古老泥岩部分的沉积率.
- 从可比的沉积环境中编译和分析了Phanerozoic数据.
- 开发了一个模型,根据沉积率来预测岩石有机含量.
主要成果:
- 古代有机丰富的泥石以非常低的沉积率 (每百万年约1米) 积累.
- 这与法内罗纪有机丰富的岩石 (10-100米/百万年) 形成鲜明对比.
- 模型的结果表明,在无氧条件下,阿尔凯初级生产率低,有机物质保存能力强.
结论:
- 古代岩石中的高有机碳含量主要是由于缓慢的积累和最小的无机稀释,而不是高生产率.
- 在无毒条件下的增强保存发挥了关键作用.
- 这使地质证据与阿古时代缓慢的碳循环相协调.
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