Formation and evolution of a reduced-type proto-atmosphere on early Earth

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03719
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Hokkaido University
• Principal Investigator: Kuramoto Kiyoshi 北海道大学, 理学研究院, 教授 (50311519)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 還元的原始大気 / 初期地球 / 流体力学的散逸 / 衝突脱ガス / 放射冷却

Outline of Final Research Achievements

Taking into account updated constraints for the composition of Earth's building blocks, a new theoretical study has been conducted to clarify the formation and evolution of the primordial atmosphere on Earth. The new model shows that impact degassing from iron-containing building blocks releases chemically reduced molecules rich in hydrogen and methane. In the early stages of Earth's accretion, gas from the solar nebula may have also been mixed into the primordial atmosphere. Our numerical simulations of atmospheric escape to space accurately include the processes of heat loss, indicating that hydrogen is leaking into space much more slowly than previously expected. This, together with the isotopic constraints on volatile elements in the Earth and primitive meteorites, suggests that a reducing atmosphere, known to be an effective site for prebiotic chemical evolution, was maintained for millions of years, including the time of the emergence of life.

Free Research Field

惑星科学

Academic Significance and Societal Importance of the Research Achievements

1980年代後半から、地球の原始大気は水蒸気と二酸化炭素を主成分とするものと考えられてきた。これに対し、本研究では地球材料物質組成に関する最新の宇宙化学的知見を取り入れ、原始地球大気の形成と進化について理論的な再考を行った。その結果、原始地球には水素やメタンに富む大気が形成され、しかも生命誕生のタイミングを含む数億年間、このような還元的な化学組成の大気が持続する可能性が高いことが分かった。還元的な原始大気は、生命に至る化学進化の場として有望であることが知られており、本成果は、地球上における生命の起源論に弾みをもたらすものである。