Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Palaeoclimates: The First Two Billion Years

James F. Kasting and Shuhei Ono
Philosophical Transactions: Biological Sciences
Vol. 361, No. 1470, Major Steps in Cell Evolution: Palaeontological, Molecular and Cellular Evidence of Their Timing and Global Effects (Jun. 29, 2006), pp. 917-929
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/20209693
Page Count: 13
  • Get Access
  • Read Online (Free)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Palaeoclimates: The First Two Billion Years
Preview not available

Abstract

Earth's climate during the Archaean remains highly uncertain, as the relevant geologic evidence is sparse and occasionally contradictory. Oxygen isotopes in cherts suggest that between 3.5 and 3.2 Gyr ago (Ga) the Archaean climate was hot (55-85 °C); however, the fact that these cherts have experienced only a modest amount of weathering suggests that the climate was temperate, as today. The presence of diamictites in the Pongola Supergroup and the Witwatersrand Basin of South Africa suggests that by 2.9 Ga the climate was glacial. The Late Archaean was relatively warm; then glaciation (possibly of global extent) reappeared in the Early Palaeoproterozoic, around 2.3-2.4 Ga. Fitting these climatic constraints with a model requires high concentrations of atmospheric CO₂ or CH₄, or both. Solar luminosity was 20-25% lower than today, so elevated greenhouse gas concentrations were needed just to keep the mean surface temperature above freezing. A rise in O₂ at approximately 2.4 Ga, and a concomitant decrease in CH₄, provides a natural explanation for the Palaeoproterozoic glaciations. The Mid-Archaean glaciations may have been caused by a drawdown in H₂ and CH₄ caused by the origin of bacterial sulphate reduction. More work is needed to test this latter hypothesis.

Page Thumbnails

  • Thumbnail: Page 
917
    917
  • Thumbnail: Page 
918
    918
  • Thumbnail: Page 
919
    919
  • Thumbnail: Page 
920
    920
  • Thumbnail: Page 
921
    921
  • Thumbnail: Page 
922
    922
  • Thumbnail: Page 
923
    923
  • Thumbnail: Page 
924
    924
  • Thumbnail: Page 
925
    925
  • Thumbnail: Page 
926
    926
  • Thumbnail: Page 
927
    927
  • Thumbnail: Page 
928
    928
  • Thumbnail: Page 
929
    929