The Long Term Carbon Cycle: changes from millenium to millenium where exchanges of carbon with rocks and oceans are very important. Budgets can be viewed here.

Examples of these chemical reactions are:

disolving CO₂: CO₂ + H₂O <---> H₂CO₃
(carbon dioxide and water yield weak carbonic acid which then weathers the surface or dissociates in oceans as below)

• chemical weathering (carbonate): CaCO₃ + H₂CO₃ ---> Ca²⁺ + 2HCO₃^-
• chemical weathering (silicate): CaSiO₃ + CO₂ + H₂CO₃^- ---> Ca²⁺ + 2HCO₃^- + SiO₂

The compounds produced by weathering then runoff into the oceans or form sediments.
• dissociation of carbonic acid(occurs in oceans): H₂CO₃ <-> H⁺ + HCO₃^-
• further dissociation of the bicarbonate ion (in oceans):  HCO₃^- <-> H⁺ + CO₃^2-

(allows the continued uptake of CO₂ by the oceans by adjusting the pH with H+ and CO₃^2- being assimilated into marine organisms to construct skeletons with Ca²⁺)