User:RockMagnetist (DCO visiting scholar)/Drafts/Geological carbon cycle

Bulk carbon content
There are large uncertainties in the bulk carbon content of the Earth and where the reservoirs are. The source of most of the material in the Earth is normally thought to be carbonaceous chondrites, which have carbon contents between 2.7 and 4.4 percent by weight. However, during accretion much of the carbon probably escaped in volatile gases such as carbon monoxide and methane. As a result, most studies estimate the carbon content to be below 0.1 wt%, and it could be as low as 50 parts per million. Models of the early Earth predict that in the first few million years of the Hadean, most of the carbon in the mantle was partitioned into the core or outgassed into the atmosphere, so the mantle would have been carbon-poor. However, over the rest of the Hadean the carbon could have been replenished by late bombardments, ingassing from the atmosphere, and metallic liquids trapped in pore spaces. The Earth's core may remain the largest reservoir.

Transport

 * Over long periods of time, the balance between weathering of silicate minerals and deposition of carbonate minerals may provide a feedback mechanism that stabilizes the concentration of carbon dioxide in the atmosphere and the surface temperature.

The geologic component of the carbon cycle operates slowly in comparison to the other parts of the global carbon cycle. It is one of the most important determinants of the amount of carbon in the atmosphere, and thus of global temperatures.

Most of the earth's carbon is stored inertly in the earth's lithosphere. Much of the carbon stored in the earth's mantle was stored there when the earth formed. Some of it was deposited in the form of organic carbon from the biosphere. Of the carbon stored in the geosphere, about 80% is limestone and its derivatives, which form from the sedimentation of calcium carbonate stored in the shells of marine organisms. The remaining 20% is stored as kerogens formed through the sedimentation and burial of terrestrial organisms under high heat and pressure. Organic carbon stored in the geosphere can remain there for millions of years.

Carbon can leave the geosphere in several ways. Carbon dioxide is released during the metamorphosis of carbonate rocks when they are subducted into the earth's mantle. This carbon dioxide can be released into the atmosphere and ocean through volcanoes and hotspots. It can also be removed by humans through the direct extraction of kerogens in the form of fossil fuels. After extraction, fossil fuels are burned to release energy, thus emitting the carbon they store into the atmosphere.