Department of Earth Sciences, Syracuse University, Syracuse, NY, USA.
Department of Earth Sciences, University of California, Riverside, Riverside, CA, USA.
Science. 2018 Jul 13;361(6398):174-177. doi: 10.1126/science.aar5372. Epub 2018 May 31.
Rising oceanic and atmospheric oxygen levels through time have been crucial to enhanced habitability of surface Earth environments. Few redox proxies can track secular variations in dissolved oxygen concentrations around threshold levels for metazoan survival in the upper ocean. We present an extensive compilation of iodine-to-calcium ratios (I/Ca) in marine carbonates. Our record supports a major rise in the partial pressure of oxygen in the atmosphere at ~400 million years (Ma) ago and reveals a step change in the oxygenation of the upper ocean to relatively sustainable near-modern conditions at ~200 Ma ago. An Earth system model demonstrates that a shift in organic matter remineralization to greater depths, which may have been due to increasing size and biomineralization of eukaryotic plankton, likely drove the I/Ca signals at ~200 Ma ago.
随着时间的推移，海洋和大气中氧气含量的上升，对地球表面环境的宜居性增强至关重要。很少有氧化还原指标可以追踪大洋上层溶解氧浓度在动物生存阈值附近的长期变化。我们提供了一个广泛的海洋碳酸盐中碘钙比（I/Ca）的汇编。我们的记录支持了大约 4 亿年前大气中氧气分压的大幅上升，并揭示了大洋上层氧气的一个阶跃式变化，使其达到了相对可持续的近现代条件，大约在 2 亿年前。一个地球系统模型表明，有机物再矿化向更深层的转移可能是由于真核浮游生物的大小和生物矿化的增加所致，这可能导致了大约 2 亿年前的 I/Ca 信号。
