Rainwater dissolves CO₂ from the air and the soil, turning into an acid weak enough to seem harmless yet strong enough to eat limestone through the reaction CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Given a million years, a whole cave system opens inside the rock, and the more acidic the water, the faster it works. The water table decides whether a chamber floods or stays air-filled — stalactites hang from the ceiling and stalagmites rise from the floor only when a drop has time to release CO₂ and precipitate calcite.
Rainwater dissolves CO₂ from the air and the soil, turning into an acid weak enough to seem harmless yet strong enough to eat limestone through the reaction CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Given a million years, a whole cave system opens inside the rock, and the more acidic the water, the faster it works. The water table decides whether a chamber floods or stays air-filled — stalactites hang from the ceiling and stalagmites rise from the floor only when a drop has time to release CO₂ and precipitate calcite.
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