Seashells are made by molluscs, which build them layer by layer from minerals in seawater.

The longer version

Mantle tissue lays down crystals of calcium carbonate inside a protein framework, drawing raw material from seawater. Because growth happens mainly at the rim, the shell records history: seasonal changes in temperature and food supply leave visible bands, much as tree rings do.

Inner layers are deposited continuously, smoothing damage and lining the soft body. Different crystal arrangements give some shells chalky hardness and others a tough, resilient structure that resists cracking. When the animal dies, soft parts vanish quickly while the shell persists, which is why beaches gather these durable remains long after their builders are gone.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.