The Carbonate-Silicate Cycle
Carbon dioxide dissolves in water to form carbonic acid.
Carbonic acid breaks down silicate rock during weathering.
Rivers carry dissolved materials to the ocean.
Precipitation of calcium carbonate and silica occurs when the ocean becomes supersaturated; also these compounds are also extracted by marine organisms to make shells which also settle to the bottom.
Metamorphism occurs as sediments are deeply buried, perhaps in subduction zones. During metamorphism, silicate materials are reformed and carbon dioxide is released through volcanoes.