A common myth is that the fossil fuel combustion (with only minor amount of fossil carbon liberated by cement- and lime production) liberated such amounts of carbon which had been deposited for tens of millions of years. However, this is not possible even theoretically: the vast majority of carbon in the sediments is in non-combustible rocks, especially carbonates and sediments with minor organic admixture (which can be metamorphosed to graphite). This can be simply verified in geological maps: sedimentary carbonates form not only the most of karst regions but also large domains in other regions formed by ancient marine sediments. In Central Apennines (Italy), the ca. 13 km thick upper crust was suggested to contain 75 % of carbonate sediments (Borexino Collaboration). This stored carbon comes from seawater and its significant portion had been recycled from atmosphere.
