Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Science 23 May 1997:
Vol. 276. no. 5316, pp. 1217 - 1221
DOI: 10.1126/science.276.5316.1217
Prev | Table of Contents | Next

Articles

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

Carl Sagan, Christopher Chyba

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.

Prior to his death in December 1996, Dr. Sagan directed the Laboratory for Planetary Studies at Cornell University, Ithaca, NY 14853-6801, USA. Dr. Chyba is in the Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721-0092, USA. Final changes in response to editors' and referees' comments were made in this manuscript by Dr. Chyba subsequent to Dr. Sagan's death.

Read the Full Text


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox.
Y. Ueno, M. S. Johnson, S. O. Danielache, C. Eskebjerg, A. Pandey, and N. Yoshida (2009)
PNAS 106, 14784-14789
   Abstract »    Full Text »    PDF »
Mineral evolution.
R. M. Hazen, D. Papineau, W. Bleeker, R. T. Downs, J. M. Ferry, T. J. McCoy, D. A. Sverjensky, and H. Yang (2008)
American Mineralogist 93, 1693-1720
   Abstract »    Full Text »    PDF »
Ozone and life on the Archaean Earth.
C. S Cockell and J. A Raven (2007)
Phil Trans R Soc A 365, 1889-1901
   Abstract »    Full Text »    PDF »
Prebiotic materials from on and off the early Earth.
M. Bernstein (2006)
Phil Trans R Soc B 361, 1689-1702
   Abstract »    Full Text »    PDF »
Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth.
F. Westall, C. E.J de Ronde, G. Southam, N. Grassineau, M. Colas, C. Cockell, and H. Lammer (2006)
Phil Trans R Soc B 361, 1857-1876
   Abstract »    Full Text »    PDF »
Fermor lecture: The influence of life on the face of the Earth: garnets and moving continents.
E. G. Nisbet (2002)
Geological Society, London, Special Publications 199, 275-307
   Abstract »    PDF »
Atmospheric Influence of Earth's Earliest Sulfur Cycle.
J. Farquhar, H. Bao, and M. Thiemens (2000)
Science 289, 756-758
   Abstract »    Full Text »
Peptide nucleic acids rather than RNA may have been the first genetic molecule.
K. E. Nelson, M. Levy, and S. L. Miller (2000)
PNAS 97, 3868-3871
   Abstract »    Full Text »    PDF »
Oceanic protection of prebiotic organic compounds from UV radiation.
H. J. Cleaves and S. L. Miller (1998)
PNAS 95, 7260-7263
   Abstract »    Full Text »    PDF »
Atmosphere-Surface Interactions on Mars: {Delta}17O Measurements of Carbonate from ALH 84001?.
J. Farquhar, M. H. Thiemens, and T. Jackson (1998)
Science 280, 1580-1582
   Abstract »    Full Text »    PDF »


To Advertise     Find Products

Science. ISSN 0036-8075 (print), 1095-9203 (online)