Cited by 396Astro and Planetary SciencePaleontology and Stratigraphy of FossilsEarth Systems and Cosmic Evolution

The Early Faint Sun Paradox: Organic Shielding of Ultraviolet-Labile Greenhouse Gases

Sagan, Carl, Chyba, Christopher·1997·Science

Abstract

Atmospheric mixing ratios of ∼10 −5 ± 1 for ammonia on the early Earth would have been sufficient, through the resulting greenhouse warming, to counteract the temperature effects of the faint early sun. One argument against such model atmospheres has been the short time scale for ammonia photodissociation by solar ultraviolet light. Here it is shown that ultraviolet absorption by steady-state amounts of high-altitude organic solids produced from methane photolysis may have shielded ammonia sufficiently that ammonia resupply rates were able to maintain surface temperatures above freezing.

Integrity signals

Registry

Crossref · 10.1126/science.276.5316.1217

Cites

89 of 89 references verified0 citation errors · 0 not checkable

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  • Possibly, a stratospheric organic haze shielded tropospheric NH3 from UV.

    “Possibly, a stratospheric organic haze, such as that on Saturn’s moon, Titan, shielded tropospheric NH3 from UV (162).”

    From The Archean atmosphere (2020) · cites this paper as [162]

  • Whether NH3 was a viable greenhouse gas is unclear.

    “Earlier, we noted that an organic haze might protect tropospheric ammonia from UV (162), but whether NH3 was a viable greenhouse gas is unclear.”

    From The Archean atmosphere (2020) · cites this paper as [162]

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Authors
Sagan, C., & Chyba, C.
Affiliations
University of Arizona (US)
Venue
Science
Published
1997-05-23
Volume
276
Issue
5316
Pages
1217-1221
ISSN
  • 0036-8075 (ISSN-L)
  • 1095-9203
OpenAlex
W1964099544
Cited by
396
References
92
Citations by year
2026: 7 · 2025: 10 · 2024: 12 · 2023: 11 · 2022: 8 · 2021: 9 · 2020: 18 · 2019: 5 · 2018: 14 · 2017: 14 · 2016: 11 · 2015: 7 · 2014: 16 · 2013: 25 · 2012: 17
FWCI
14.02
Type
journal article
Language
en
Open access
closed
Locations
  • Science (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Earth Systems and Cosmic Evolution
Keywords
early Earth, ammonia, greenhouse gases, UV protection, organic solids, methane photolysis, ammonia photodissociation, atmospheric mixing ratios, surface temperature, early atmosphere
MeSH terms
Ammonia, Atmosphere, Carbon Dioxide, Methane, Models, Chemical, Photolysis, Ultraviolet Rays, Solar System, Greenhouse Effect, Earth, Planet, Evolution, Planetary

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