Because they depend on sunlight for photosynthesis, diatoms generally live in the upper 200 meters of oceans and bodies of fresh water.These algae hardly look like plants, but more like flying saucers, tiny canoes or cigars, lobed leaves, the undersides of mushroom caps, striated ribbons, or filigreed Christmas ornaments. Whatever their shape, all diatoms have shell-like, brittle cell walls made out of silica (glass) and pectin. The walls are two interlocking halves or shells that fit together like a pillbox.
Because they depend on sunlight for photosynthesis, diatoms generally live in the upper 200 meters of oceans and bodies of fresh water.
Some species of diatoms simply float in the water currents near the surface. Others attach themselves to larger floating objects or to the sea floor. When diatoms die, they slowly sink to the sea floor. The buildup of trillions of these shells forms a crumbly white sediment known as diatomaceous earth or diatomite, which is used in manufacturing pool filters and abrasives, including toothpaste.