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Prebiotic atmosphere

The pale orange dot, an artist's impression of the early Earth which is believed to have appeared orange through its hazy methane rich prebiotic second atmosphere, being somewhat comparable to Titan's atmosphere[1]

The prebiotic atmosphere is the second atmosphere present on Earth before today's biotic, oxygen-rich third atmosphere, and after the first atmosphere (which was mainly water vapor and simple hydrides) of Earth's formation. The formation of the Earth, roughly 4.5 billion years ago,[2] involved multiple collisions and coalescence of planetary embryos.[3] This was followed by a <100 million year period on Earth where a magma ocean was present, the atmosphere was mainly steam, and surface temperatures reached up to 8,000 K (14,000 °F).[4] Earth's surface then cooled and the atmosphere stabilized, establishing the prebiotic atmosphere. The environmental conditions during this time period were quite different from today: the Sun was ~30% dimmer overall yet brighter at ultraviolet and x-ray wavelengths,[5][6] there was a liquid ocean, it is unknown if there were continents but oceanic islands were likely,[7][8] Earth's interior chemistry (and thus, volcanic activity) was different,[9] and there was a larger flux of impactors (e.g. comets and asteroids) hitting Earth's surface.[10]

Studies have attempted to constrain the composition and nature of the prebiotic atmosphere by analyzing geochemical data and using theoretical models that include our knowledge of the early Earth environment. These studies indicate that the prebiotic atmosphere likely contained more CO2 than the modern Earth, had N2 within a factor of 2 of the modern levels, and had vanishingly low amounts of O2.[9] The atmospheric chemistry is believed to have been "weakly reducing", where reduced gases like CH4, NH3, and H2 were present in small quantities.[9] The composition of the prebiotic atmosphere was likely periodically altered by impactors, which may have temporarily caused the atmosphere to have been "strongly reduced".[11]

Constraining the composition of the prebiotic atmosphere is key to understanding the origin of life, as it may facilitate or inhibit certain chemical reactions on Earth's surface believed to be important for the formation of the first living organism. Life on Earth originated and began modifying the atmosphere at least 3.5 billion years ago and possibly much earlier,[12] which marks the end of the prebiotic atmosphere.

  1. ^ Trainer, Melissa G.; Pavlov, Alexander A.; DeWitt, H. Langley; Jimenez, Jose L.; McKay, Christopher P.; Toon, Owen B.; Tolbert, Margaret A. (2006-11-28). "Organic haze on Titan and the early Earth". Proceedings of the National Academy of Sciences. 103 (48): 18035–18042. doi:10.1073/pnas.0608561103. ISSN 0027-8424. PMC 1838702. PMID 17101962.
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  9. ^ a b c Catling, David C. (2017). Atmospheric Evolution on Inhabited and Lifeless Worlds. James F. Kasting. West Nyack: Cambridge University Press. ISBN 978-1-139-02055-8. OCLC 982451455.
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  12. ^ Schopf, J. William; Kudryavtsev, Anatoliy B.; Czaja, Andrew D.; Tripathi, Abhishek B. (2007). "Evidence of Archean life: Stromatolites and microfossils". Precambrian Research. 158 (3–4): 141–155. Bibcode:2007PreR..158..141S. doi:10.1016/j.precamres.2007.04.009. ISSN 0301-9268.

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