早期还原地球大气中的自屏蔽强化有机物合成。

IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS
Astrobiology Pub Date : 2024-11-01 Epub Date: 2024-10-22 DOI:10.1089/ast.2024.0048
Tatsuya Yoshida, Shungo Koyama, Yuki Nakamura, Naoki Terada, Kiyoshi Kuramoto
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引用次数: 0

摘要

预计地球是通过含有金属 Fe 的构件的吸积和/或周围星云气体的引力捕获,获得了富含 H2 和 CH4 的还原型原大气层。这样一个覆盖着原海洋的湿润、还原的早期大气层最终会通过光化学过程向氧化化学成分演化,其中包括与 H2O 衍生的氧化自由基发生反应,以及选择性地将氢逸散到太空中。在此期间,大气中的 CH4 可能经过光化学再处理,不仅生成含 C 的氧化物,还生成有机物。然而,有机物的形成与氧化之间的分枝比尽管对早期地球的非生物化学演化具有重要意义,但至今仍不为人所知。在这里,我们通过数值分析表明,在富含 H2 和 CH4 的湿原大气的光化学演化过程中,气态碳氢化合物(如 C2H2 和 C3H4)对紫外线的吸收显著抑制了 H2O 的光解和随后的 CH4 氧化。因此,近一半的初始 CH4 转化为较重的有机物,同时在原始海洋表面沉积了 HCN 和 H2CO 等前生物必需分子,地质时间尺度为 10-100 Myr。我们的研究结果表明,原初海洋中有机物和生物前重要分子的积累可能会产生富含各种有机物的汤,这可能最终导致生物的出现。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere.

Earth is expected to have acquired a reduced proto-atmosphere enriched in H2 and CH4 through the accretion of building blocks that contain metallic Fe and/or the gravitational trapping of surrounding nebula gas. Such an early, wet, reduced atmosphere that covers a proto-ocean would then ultimately evolve toward oxidized chemical compositions through photochemical processes that involve reactions with H2O-derived oxidant radicals and the selective escape of hydrogen to space. During this time, atmospheric CH4 could be photochemically reprocessed to generate not only C-bearing oxides but also organics. However, the branching ratio between organic matter formation and oxidation remains unknown despite its significance on the abiotic chemical evolution of early Earth. Here, we show via numerical analyses that UV absorptions by gaseous hydrocarbons such as C2H2 and C3H4 significantly suppress H2O photolysis and subsequent CH4 oxidation during the photochemical evolution of a wet proto-atmosphere enriched in H2 and CH4. As a result, nearly half of the initial CH4 converted to heavier organics along with the deposition of prebiotically essential molecules such as HCN and H2CO on the surface of a primordial ocean for a geological timescale order of 10-100 Myr. Our results suggest that the accumulation of organics and prebiotically important molecules in the proto-ocean could produce a soup enriched in various organics, which might have eventually led to the emergence of living organisms.

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来源期刊
Astrobiology
Astrobiology 生物-地球科学综合
CiteScore
7.70
自引率
11.90%
发文量
100
审稿时长
3 months
期刊介绍: Astrobiology is the most-cited peer-reviewed journal dedicated to the understanding of life''s origin, evolution, and distribution in the universe, with a focus on new findings and discoveries from interplanetary exploration and laboratory research. Astrobiology coverage includes: Astrophysics; Astropaleontology; Astroplanets; Bioastronomy; Cosmochemistry; Ecogenomics; Exobiology; Extremophiles; Geomicrobiology; Gravitational biology; Life detection technology; Meteoritics; Planetary geoscience; Planetary protection; Prebiotic chemistry; Space exploration technology; Terraforming
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