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How do dissolved carbon dioxide and water help weather calcium from continental rocks?

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Diagram illustrating Earth's environmental spheres, with labeled sections showing the geosphere (land and crust), biosphere (living things), atmosphere (air), and hydrosphere (water), each extending vertically from the Earth's surface. — hydrosphere Earth's environment includes the atmosphere, the hydrosphere, the lithosphere, and the biosphere.

When carbon dioxide ( $C O_{2}$ ) dissolves in water, it reacts to form a weak acid known as carbonic acid ( $H_{2} C O_{3}$ ). This acidic solution plays a fundamental role in the chemical weathering of continental rocks.125

When this carbon dioxide-charged water comes into contact with rocks containing calcium, such as limestone (which is primarily composed of calcite), the acid reacts with the mineral to dissolve it. This process releases calcium ions ( $C a^{2 +}$ ) and bicarbonate ions ( $H C O_{3}^{-}$ ) into the water. The reaction can be summarized as follows:34

$C a C O_{3} (s) + C O_{2} (g) + H_{2} O (l) \to C a^{2 +} (a q) + 2 H C O_{3}^{-} (a q)$ 4

These dissolved constituents are subsequently transported by groundwater and river systems to the oceans. Once in the marine environment, these ions can combine to form new calcium carbonate, which may eventually settle on the seafloor to form sedimentary rocks, continuing the geologic carbon cycle.542