Hydrodynamic escape of an impact-generated reduced proto-atmosphere on Earth
Hydrodynamic escape of an impact-generated reduced proto-atmosphere on Earth
复制标题
地球上因撞击而产生的原始大气减少的流体动力逃逸
DOI：
10.1093/mnras/stab1471
复制
发表时间：
2021
影响因子：
4.8
通讯作者：
Kuramoto Kiyoshi
中科院分区：
文献类型：
--
作者：
Yoshida Tatsuya;Kuramoto Kiyoshi
最近的宇宙化学研究表明，地球的大部分组成元素在同位素组成上接近顽辉石陨石。这意味着在吸积的地球上形成了一个由撞击引起的富含h2和ch4的原始大气。由于流体动力学的逃逸，这种减少的原始大气将在很大程度上消失，但它的通量和氢耗尽的时间尺度仍然高度不确定。本文通过扩展化学网络和辐射冷却过程，对这种h2 - ch4原大气进行了一维流体动力学逃逸模拟，以估计早期地球富h2表面环境的持续时间。在逸出液中，ch4通过直接光解和光化学反应产生的离子进行有效解离。另一方面，光化学产物如H、CH和ch3的辐射冷却显著抑制了大气逸出。尽管CH4和它们的浓度都很小，但在低层大气中，当CH4/H2= 0.007时，热效率下降，当CH4/H2 > 0.01时，CH4的逸出可以忽略不计。根据同位素组成和当前地球上碳、氮含量的限制，氢逸出的时间尺度可能超过数亿年。我们的研究结果表明，在地球最初的几亿年里，一个长期的富氢还原环境在气候变暖和与生物出现有关的有机质的产生中发挥了重要作用。
Recent cosmochemical studies have shown that most of Earth’s building blocks were close to enstatite meteorites in isotopic compositions. This implies the formation of an impact-induced proto-atmosphere enriched in H2and CH4on accreting Earth. Such a reduced proto-atmosphere would have been largely lost by hydrodynamic escape, but its flux and time-scale for hydrogen depletion remain highly uncertain. Here we carry out 1D hydrodynamic escape simulations for such an H2–CH4proto-atmosphere by incorporating expanded chemical networks and radiative cooling processes for estimation of the duration of the H2-rich surface environment on early Earth. In the escape outflow, CH4is dissociated effectively by direct photolysis and chemical reactions with photochemically produced ion species. On the other hand, radiative cooling by photochemical products such as H, CH, and CH3significantly suppresses atmospheric escape. Even though CH4and their concentrations are small, the heating efficiency decreases towhen CH4/H2= 0.007 in the lower atmosphere and CH4would suffer negligible escape when CH4/H2≳ 0.01. The time-scale for H2escape consistent with the constraints of the isotopic compositions and the amount of C and N on the present Earth is possibly more than several hundred million years. Our results suggest that a long-lived hydrogen-rich reduced environment played important roles in climate warming and the generation of organic matters linked to the emergence of living organisms during the first several hundred million years of Earth.
登录
查看更多内容
太阳 EUV 照射导致原始陆地大气的耗散
影响因子：
--
作者：
M. Sekiya;K. Nakazawa;C. Hayashi
通讯作者：
C. Hayashi
流体动力学逃逸中的质量分馏
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
D. Hunten;R. Pepin;James C. G. Walker
通讯作者：
James C. G. Walker
太阳变化物理学
DOI：
10.1007/978-94-010-9633-1
发表时间：
1981
期刊：
影响因子：
--
作者：
V. Domingo
通讯作者：
V. Domingo
含有 CH4、CO 和 CO2 的大气中的益生元合成
影响因子：
3.9
作者：
G. Schlesinger;S. Miller
通讯作者：
S. Miller
地球核心形成过程中H和C在地幔和地核之间的分配：其对大气演化和早期地幔氧化还原状态的影响
影响因子：
--
作者：
K. Kuramoto;T. Matsui
通讯作者：
T. Matsui