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Theoretical constraints on oxygen and carbon dioxide concentrations in the Precambrian atmosphereSimple (one-dimensional) climate models suggest that carbon dioxide concentrations during the Archean must have been at least 100-1000 times the present level to keep the Earth's surface temperature above freezing in the face of decreased solar luminosity. Such models provide only lower bounds on CO2, so it is possible that CO2 levels were substantially higher than this and that the Archean climate was much warmer than today. Periods of extensive glaciation during the early and late Proterozoic, on the other hand, indicate that the climate at these times was relatively cool. To be consistent with climate models CO2 partial pressures must have declined from approximately 0.03 to 0.3 bar around 2.5 Ga ago to between 10(-3) and 10(-2) bar at 0.8 Ga ago. This steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data, which implies that pCO2 did not change appreciably during that time. Oxygen was essentially absent from the Earth's atmosphere and oceans prior to the emergence of a photosynthetic source, probably during the late Archean. During the early Proterozoic the atmosphere and surface ocean were apparently oxidizing, while the deep ocean remained reducing. An upper limit of 6 x 10(-3) bar for pO2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean. The establishment of oxidizing conditions in the deep ocean, marked by the disappearance of banded iron formations approximately 1.7 Ga ago, permitted atmospheric oxygen to climb to its present level. O2 concentrations may have remained substantially lower than today, however, until well into the Phanerozoic.
Document ID
20040089098
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Kasting, J. F.
(NASA Ames Research Center Moffett Field CA United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 1987
Publication Information
Publication: Precambrian research
Volume: 34
ISSN: 0301-9268
Subject Category
Geosciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Review, Tutorial
Review
NASA Discipline Exobiology
NASA Center ARC

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