Carbonate–silicate cycle

On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.

[9] The chemical pathway is as follows: River runoff carries these products to the ocean, where marine calcifying organisms use Ca2+ and HCO3− to build their shells and skeletons, a process called carbonate precipitation: Two molecules of CO2 are required for silicate rock weathering; marine calcification releases one molecule back to the atmosphere.

The calcium carbonate (CaCO3) contained in shells and skeletons sinks after the marine organism dies and is deposited on the ocean floor.

[8] Over tens to hundreds of millions of years, carbon dioxide levels in the atmosphere may vary due to natural perturbations in the cycle[10][11][12] but even more generally, it serves as a critical negative feedback loop between carbon dioxide levels and climate changes.

The advent of carbonate biomineralization near the Precambrian-Cambrian boundary would have allowed more efficient removal of weathering products from the ocean.

For example, the uplift of major mountain ranges, such as Himalayas and the Andes, is thought to have initiated the Late Cenozoic Ice Age due to increased rates of silicate weathering and draw down of carbon dioxide.

[21] Observations of so-called deep time indicate that Earth has a relatively insensitive rock weathering feedback, allowing for large temperature swings.

Human emissions of CO2 have been steadily increasing, and the consequent concentration of CO2 in the Earth system has reached unprecedented levels in a very short amount of time.

Located at the edge of the solar system's habitable zone, its surface is too cold for liquid water to form without a greenhouse effect.

In attempting to explain topographical features resembling fluvial channels, despite seemingly insufficient incoming solar radiation, some have suggested that a cycle similar to Earth's carbonate-silicate cycle could have existed – similar to a retreat from Snowball Earth periods.

[26] It has been shown using modeling studies that gaseous CO2 and H2O acting as greenhouse gases could not have kept Mars warm during its early history when the Sun was fainter because CO2 would condense out into clouds.

After losing its water by photodissociation and hydrogen escape, Venus stopped removing carbon dioxide from its atmosphere, and began instead to build it up, and experience a runaway greenhouse effect.

On tidally locked exoplanets, the location of the substellar point will dictate the release of carbon dioxide from the lithosphere.

This figure describes the geological aspects and processes of the carbonate silicate cycle, within the long-term carbon cycle.
This schematic shows the relationship between the different physical and chemical processes that make up the carbonate-silicate cycle.
Microscopic shells of Foraminifera found in sediment cores may be used to determine past climate conditions including ocean temperatures and aspects of atmospheric chemistry.