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carbonate-silicate cycle

(reversible carbon/silicon chemical reaction)

The carbonate-silicate cycle is a naturally-occurring geochemical cycle incorporating the chemical reaction:

CaSiO3 + CO2 ⇔ CaCO3 + SiO2


calcium silicate + carbon dioxide ⇔ calcium carbonate + silicon dioxide

At the surface of the Earth, the balance is in favor of carbonates (i.e., dissipating carbon dioxide), but at temperatures of 300K, the balance is toward silicates. The surface of Venus tends toward the latter as do subsurface conditions of Earth.

The cycle helps stabilize climate in that rain with carbon dioxide hitting rocks causes the reaction (weathering), which dissipates carbon dioxide and carries it into the ocean. Living organisms incorporate it in shells, and after dying, are incorporated into the under-ocean strata, which eventually reach the depth where the reaction tends toward the silicates and carbon dioxide. Volcanic eruptions eventually send the resulting CO2 back into the atmosphere.

The ability to complete this cycle affects an extra-solar planet's ability to maintain liquid water. Thus signs suggesting a planet has this ability affects habitability and is of interest in astrobiology.


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