Evolution of early-Earth atmophere with reduced chemical compositions

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03638
• 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): 2021-04-01 – 2024-03-31
• Keywords: 原始地球大気 / 水素 / メタン / 水 / 流体力学的散逸 / 大気光化学 / 有機物 / 大気進化

Outline of Final Research Achievements

Thermodynamic calculations using the elemental composition of carbonaceous asteroid Ryugu samples reveal that hydrogen is thermally released at high yields even from carbonaceous meteorite-like compositions, which are the most oxidizing among Earth material materials. The formation of a hydrogen-rich proto-atmosphere is considered to have been inevitable on Earth. Hydrodynamic escape of hydrogen and atmospheric photochemical processes driven by the short-wavelength component of solar radiation were carefully simulated numerically. The results revealed that radiative cooling of CH4, H2O, and their photolysis products slows down the hydrogen loss that requires atmospheric heating and that organic molecules photochemically generated from CH4 shield solar UV light and inhibit the photolysis of H2O, preventing the production of O atoms and OH radicals that serve as oxidants, thereby self-promoting organic polymerization.

Free Research Field

惑星科学

Academic Significance and Societal Importance of the Research Achievements

本研究成果は、長期持続する還元的原始大気において、大量の水溶性有機物と不溶性有機物凝縮相の生産が起き、生命誕生に至る化学進化の場を地球表層に全球規模でもたらした可能性を示唆している。これまでは、還元的な原始大気からは速やかに水素が流失してしまい、原始大気における有機分子の生成は起きても限定的とする考えが主流だった。本研究は、地球上での生命の起源という、一般市民の関心も惹きつける重要な未解決問題に対し、理論的裏付けをもった斬新な化学進化の場の描像を提供した。