Earth’s past holds the key to unlocking the secrets of alien worlds. Scientists from Tohoku University, Tokyo University, and Hokkaido University are using atmospheric models to rewind time and explore the origins of life on our own planet.
“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.
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However, understanding the role of UV radiation in Earth’s early atmosphere is challenging. This early atmosphere was highly unstable and subject to rapid chemical changes. Additionally, the exact rate and mechanism of water vapor breakdown by UV radiation and subsequent molecule formation remain uncertain.
To address these uncertainties, a 1D photochemical model was developed to simulate Earth’s ancient atmosphere. This model suggests that significant hydrogen loss occurred to space, and that hydrocarbons like acetylene (derived from methane) acted as a UV shield. By reducing water vapor breakdown and methane oxidation, this UV shielding promoted the accumulation of organic compounds. If Earth’s initial methane abundance was comparable to its current carbon content, organic layers hundreds of 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.
