Carbonate minerals and the co2-carbonic acid system

Dissolved CO2 in aqueous solution in the form of carbonic acid and carbonate ions has played a key role in processes at the Earth’s surface over its entire history. Weathering reactions and subsequent precipitation of carbonate sediments together with biological production and burial of organic matter have removed 2.85 × 1020 kg of CO2 from the atmosphere, leaving there 0.001% of the original mass. Cycling of CO2 between dissolved forms in the ocean, gaseous form in the atmosphere, and carbonate sediments continues to exert a major control on Earth’s climate. Dissolved carbonate exerts a major control on the pH of seawater and other natural waters. Burning of fossil fuels and other anthropogenic activities is increasing the amount of dissolved CO2 in the ocean and reducing ocean pH, threatening carbonate-secreting organisms such as corals. Carbonate minerals, primarily calcite and dolomite precipitating from these solutions, constitute the second most abundant class sedimentary rocks.