Quantifying The Biotic Enhancement Of Weathering And Its Implications

Quantitative estimate of biotic enhancement factor on present Earth surface. Parameterization of the effects of temperature, atmospheric carbon dioxide partial pressure, runoff on weathering rate. My decomposition of the combined effects in chemical denudation. Would the present abiotic Earth be habitable? The biotic factor in GEOCARB. Progress report: what is the cumulative biotic enhancement of weathering?

The role of land biota in affecting chemical weathering rates and the carbon cycle is now under active investigation. Estimates of the present biotic enhancement of weathering range over at least two orders of magnitude. Laboratory and field studies have provided invaluable clues. Another approach has been constructing a model of the temperature/atmospheric pCO2 history of the Earth's surface based on the silicate-carbonate biogeochemical cycle and testing it with empirical data, a procedure followed for the Phanerozoic by Berner (1993, 1994). We have attempted an analogous approach for Earth history dating back to about 4 Ga (Schwartzman and Shore 1996). This approach will be discussed at length in chapter 8, but it will begin here in model calculations of the likely conditions on an abiotic Earth. We will first look at the basis for a quantitative estimate of the present biotic enhancement of weathering and a systematic parameterization of the various influences on the natural weathering rate. My decomposition of the combined processes leading to typical observed chemical denudation rates in the field will then be discussed. Finally, the biotic factor in weathering will be rejoined in a discussion of GEOCARB.

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