Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA.
Proc Natl Acad Sci U S A. 2012 Mar 20;109(12):4371-6. doi: 10.1073/pnas.1115705109. Epub 2012 Mar 5.
Oxygen and hydrogen isotope compositions of Earth's seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth's oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.
地球海水的氧和氢同位素组成受地幔、岩石圈（海洋和大陆地壳）和大气储层之间的挥发物通量控制。在整个地质时期，这些地球系统储层中的氧质量预算可能是守恒的，但氢的质量预算则不然，因为氢可以逸散到太空中。来自格陵兰岛西部约 38 亿年伊苏瓦超群的蛇纹石的同位素性质用于描述古代海水的氢和氧同位素组成。太古宙海洋的氘含量（相对于维也纳标准平均海水（VSMOW）表示为 δD）最多减少了 25±5‰，但氧同位素比值与现代海洋相当。全球氢预算的质量平衡约束了大陆生长和行星氢损失对地球海洋中氢同位素比值长期演化的贡献。我们的计算预测，早期地球的海洋体积增加了多达 26%，并且从限制氢逸散到太空中推断出的大气 CH4 和 CO2 浓度与太古宙地球的温和条件一致。
