It is as if water has acted as the priest in a chemical marriage between carbon dioxide and calcium. This trapped carbon dioxide is washed down to oceans via rivers and groundwater. When these micro-organisms die, their bodies sink to the bottom of the ocean, and over millions of years these form massive deposits of chalk, such as the white cliffs of Dover. These chalk deposits can remain intact for hundreds, sometimes thousands, of millions of years, and are Gaia's only very long-term storage for carbon dioxide stripped from the atmosphere. Eventually, some chalk is subducted by the incessant, gradual movements of the Earth's great tectonic plates into the depths of the Earth.
Carbon dioxide is a greenhouse gas.
The drawdown of carbon dioxide via rock weathering is painfully slow from a human perspective, too slow to solve the problem of global warming. The carbon dioxide which we have put into the atmosphere will take more than 500,000 years to find itself locked up in chalk sediments at the bottom of the sea. We know that neither of these life-destroying events has happened because life is abundantly present throughout the fossil record. Gaia seems to have a thermostat which has kept temperatures right for life over the 3.8 billion years of life's tenure on the planet, and it turns out that this involves the rock-weathering process we have just mentioned. Imagine a period of intense volcanic activity which releases billions of tonnes of carbon dioxide into the atmosphere.