Large amounts of organic matter formed in the early Earth's atmosphere — Tohoku University, et al. hope to uncover the origin of life

A research group comprising Project Researcher Tatsuya Yoshida, Professor Naoki Terada, and Graduate Student Shungo Koyama of the Graduate School of Science at Tohoku University, Project Researcher Yuki Nakamura of the Graduate School of Science at the University of Tokyo, and Professor Kiyoshi Kuramoto of the Faculty of Science at Hokkaido University jointly developed an atmospheric evolution model that considers various chemical reactions in the atmosphere and the escape of air into space. By estimating the evolution process of the early Earth's atmosphere, which was rich in hydrogen and methane, and production of organic matter during that time, they revealed that an organic matter layer with a thickness of several hundred meters might have been deposited on the Earth surface in ancient times. This finding is expected to lead to the uncovering of the origin of life on Earth. The results are published in the international journal Astrobiology on October 22.

Recent studies investigating Earth formation indicated that the majority of the Earth's materials are rich in metallic iron. Because metallic iron is a strong reducing agent, the Earth's atmosphere at that time, which is rich in hydrogen and methane, must be very different from today. Such an atmosphere is unstable, and if water vapor is efficiently decomposed by UV radiation, highly reactive molecules that cause oxidation, such as hydroxyl radicals, will be produced, accelerating the production of oxides, including carbon monoxide and carbon dioxide. However, it was unclear to what extent or on what time scale will the production of organic matter and oxides originating from methane occur in an atmosphere rich in hydrogen and methane.

In this study, the researchers developed the atmospheric evolution model that considers various chemical reactions in the atmosphere and the escape of air into space. They estimated the production of organic matter during the evolution of the Earth's early atmosphere, which was rich in hydrogen and methane. Model calculations show that when hydrogen escapes into space and the atmosphere predominantly contains methane, hydrocarbon gases, such as acetylene, produced from methane block UV radiation, substantially suppressing the decomposition of water vapor and subsequent oxidation of methane. This process promotes organic matter formation.

Owing to the UV self-shielding effect of the produced organic matter, most methane was converted into organic matter, which eventually deposited on the Earth surface, forming an organic layer with a thickness of hundreds of meters. Among the organic matter produced are those that form the basis for amino acids and nucleic acids, the materials responsible for life. The deposition of these materials on the Earth's surface led to the formation of oceans and lakes containing high concentrations of these materials, indicating that chemical evolution that followed may have led to the birth of life.

In recent years, various organic materials have been discovered on the surface of Mars. Comparison of these data with findings from planetary explorations is expected to deepen our understanding of the universality and uniqueness of atmospheric evolution and emergence of life on Earth.

Yoshida said, "We have been conducting research based on the expectation that the early Earth's atmosphere played an important role in the birth of life, but the results we obtained this time far exceeded our expectations. We hope to use this research as a steppingstone to deepen our understanding of the Earth's evolution leading up to the birth of life, which still remains a mystery, by combining evidence from material science on Earth and knowledge of other planets obtained through planetary explorations."

Journal Information
Publication: Astrobiology
Title: Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere
DOI: 10.1089/ast.2024.0048