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Carbon Dioxide Cycling And The Climate of Ancient EarthThe continental cycle of silicate weathering and metamorphism dynamically buffers atmospheric CO2 and climate. Feedback is provided by the strong temperature dependence of silicate weathering. Here we argue that hydrothermal alteration of oceanic basalts also dynamically buffers CO2. The oceanic cycle links with the mantle via subduction and the midocean ridges. Feedback is provided by the dependence of carbonatization on dissolved carbonates in seawater. Unlike the continental cycle, the oceanic cycle has no thermostat. Currently the continental cycle is more important, but earlier in Earth's history, especially if heat flow were higher than it is now, more vigorous plate tectonics would have made the oceanic cycle dominant. We find that CO2 greenhouses thick enough to defeat the faint early sun are implausible and that, if no other greenhouse gases are invoked, very cold climates are expected for much of the Proterozoic and the Archean. We echo current fashion and favor biogenic methane as the chief supplement to CO2. Fast weathering and probable subduction of abundant impact ejecta would have reduced CO2 levels still further in the Hadean. Despite its name, the Hadean would have been the coldest era in the history of the Earth.
Document ID
20010064077
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Zahnle, Kevin
(NASA Ames Research Center Moffett Field, CA United States)
Sleep, Norman H.
(Stanford Univ. Stanford, CA United States)
DeVincenzi, Donald
Date Acquired
August 20, 2013
Publication Date
January 1, 2001
Subject Category
Environment Pollution
Meeting Information
Meeting: NASA Astrobiology Institute Meeting
Country: United States
Start Date: April 10, 2001
End Date: April 12, 2001
Sponsors: NASA Headquarters
Funding Number(s)
PROJECT: RTOP 344-33-10-18
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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