Final answer:
Limestones are formed from skeletal remains of coral and other lime-secreting sea animals. When a saturated solution of CaCO3 in CO2-rich water rises toward Earth's surface or is otherwise heated, CO₂ gas is released as the water warms and CaCO3 precipitates from the solution.
Step-by-step explanation:
Limestones are formed from skeletal remains of coral and other lime-secreting sea animals. Limestone deposits that form caves consist primarily of CaCO3 from the remains of living creatures such as clams and corals. When a saturated solution of CaCO3 in CO2-rich water rises toward Earth's surface or is otherwise heated, CO₂ gas is released as the water warms and CaCO3 precipitates from the solution.