Japanese researchers developed a model to simulate early Earth’s atmosphere, revealing how UV radiation and hydrocarbons influenced organic formation. They found ancient Earth resembled Venus and Mars, prompting questions about Earth’s unique path to life.
The journey to uncovering the mysteries of distant planets begins here on Earth. Scientists from Tohoku University, the University of Tokyo, and Hokkaido University have created a model that factors in diverse atmospheric chemical reactions, providing insights into how Earth’s atmosphere—and potentially the first traces of life—evolved.
“Ancient Earth was nothing like our current home,” explains Shungo Koyama (Tohoku University), “It was a much more hostile place; rich in metallic iron with an atmosphere containing hydrogen and methane.”
These molecules contain an important clue to how life was initially formed. When exposed to solar ultraviolet (UV) radiation, they undergo a chemical reaction that produces organics (also known as the “building blocks of life”). Part of these organics were precursors to essential biomolecules, such as amino acids and nucleic acids.
Challenges in Studying Ancient UV Radiation
However, understanding the role of UV radiation is difficult. Firstly, this type of atmosphere is unstable and likely underwent rapid changes due to atmospheric chemical reactions.
Secondly, when UV radiation efficiently breaks down water vapour in the atmosphere and forms oxidative molecules, the precise branching ratio and timescale has not been determined. In order to address these issues, a 1D photochemical model was created to make accurate predictions about what the atmosphere was like on Earth long ago.
Key Findings: Hydrogen Loss and UV Shielding by Hydrocarbons
The calculation reveals that most hydrogen was lost to space and that hydrocarbons like acetylene (produced from methane) shielded UV radiation. This inhibition of UV radiation significantly reduced the breakdown of water vapor and subsequent oxidation of methane, thus enhancing the production of organics.
If the initial amount of methane was equivalent to that of the amount of carbon found on the present-day Earth’s surface, organic layers several hundred meters thick could have formed.
“There may have been an accumulation of organics that created what was like an enriched soup of important building blocks. That could have been the source from which living things first emerged on Earth.” Tatsuya Yoshida (Tohoku University) proposes.
The model suggests that the atmosphere on ancient Earth was strikingly similar to what we see on current day neighbouring planets: Venus and Mars. However, despite their proximity, Earth evolved into a completely different environment. Researchers are trying to understand what makes Earth so special.
As such, this model allows us to deepen our understanding of whether atmospheric evolution and the origin of life on Earth are unique or share common patterns with other planetary systems.
Reference: “Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth’s Atmosphere” by Tatsuya Yoshida, Shungo Koyama, Yuki Nakamura, Naoki Terada and Kiyoshi Kuramoto, 22 October 2024, Astrobiology.
DOI: 10.1089/ast.2024.0048
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