Photochemical Consequences of Enhanced CO2 Levels in Earth's Early Atmosphere

  1. E.T. Sundquist and
  2. W.S. Broecker
  1. James F. Kasting

Published Online: 18 MAR 2013

DOI: 10.1029/GM032p0612

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

How to Cite

Kasting, J. F. (1985) Photochemical Consequences of Enhanced CO2 Levels in Earth's Early Atmosphere, in The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0612

Author Information

  1. NASA Ames Research Center, Moffett Field, California 94035

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900605

Online ISBN: 9781118664322

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Keywords:

  • Carbon cycle (Biogeochemistry)—Congresses;
  • Atmospheric carbon dioxide—Congresses;
  • Geological time—Congresses;
  • Paleothermometry—Congresses;
  • Geology, Stratigraphic—Congresses

Summary

Greatly enhanced atmospheric CO2 concentrations are the most likely mechanism for offsetting the effects of reduced solar luminosity early in the earth's history. CO2 levels of 80 to 600 times the present value could have maintained a mean surface temperature of 0°C to 15°C, given a 25% decrease in solar output. Such high CO2 levels are at least qualitatively consistent with our present understanding of the carbonate-silicate geochemical cycle. The presence of large amounts of CO2 has important implications for the composition of the earth's prebiotic atmosphere. The hydrogen budget of a high-CO2 primitive atmosphere would have been strongly influenced by rainout of H2O2 and H2CO. The reaction of H2O2 with dissolved ferrous iron in the early oceans could have been a major sink for atmospheric oxygen. The requirement that this loss of oxygen be balanced by a corresponding loss of hydrogen (by escape to space and rainout of H2CO) implies that the atmospheric H2 mixing ratio was greater than 2×10−5 and the ground level O2 mixing ratio was below 10−12, even if other surface sources of H2 were small. These results are only weakly dependent on changes in solar UV flux, rainout rates, and vertical mixing rates in the primitive atmosphere.