2.3.13 (HL)—Carbonate fossilization

Corals and molluscs build calcium-carbonate hard parts; after burial, some become part of long-lived limestone stores.

Dissolved carbon is incorporated into shell or skeleton, then death, sedimentation and lithification can transfer it to rock. This is one pathway among several, not a complete cycle by itself.

A dead mollusc shell settles on the seabed; buried carbonate may later lithify, moving carbon from a biological store to the lithosphere.

Burial and lithification; merely producing a shell does not guarantee long-term storage.

Not every shell is preserved, and limestone formation is not the same as immediate shell growth.