The precipitation of calcium carbonate is important as it results in a loss of alkalinity as well as a release of CO (Equation 4), and therefore a change in the rate of preservation of calcium carbonate can alter the partial pressure of CO in Earths atmosphere. CaCO is supersatured in the great majority of ocean surface waters and undersaturated at depth, meaning the shells are more likely to dissolve as they sink to ocean depths.  CaCO can also be dissolved through metabolic dissolution (i.e. can be used as food and excreted) and thus deep ocean sediments have very little calcium carbonate.  The precipitation and burial of calcium carbonate in the ocean removes particulate inorganic carbon from the ocean and ultimately forms limestone. On time scales greater than 500,000 years Earths climate is moderated by the flux of carbon in and out of the lithosphere. Rocks formed in the ocean seafloor are recycled through plate tectonics back to the surface and weathered or subducted into the mantle, the carbon outgassed by volcanoes.