concept

Carbonate-silicate cycle

Earth's long-term thermostat - a geochemical loop turning over every few hundred thousand years that has kept the planet habitable for nearly four billion years. Atmospheric CO₂ dissolves in rain to make a weak acid that weathers continental silicate rock; the products wash to the sea, where marine life locks them into calcium carbonate shells that sink to become seafloor rock, pulling carbon out of the air; tectonics subducts that rock, cooks it, and volcanoes breathe the CO₂ back out. The key: weathering speeds up with temperature, so when the planet warms, faster weathering draws down CO₂ and cools it back - a self-correcting negative feedback. It is the resolution of the faint young sun paradox.