What are shells made of? what happens when they fall to the bottom of he ocean?

Most shells that are found on beaches are the shells of marine mollusks, partly because these shells are usually made of calcium carbonate, and endure better than shells made of chitin. Apart from mollusk shells, other shells that can be found on beaches are those of barnacles, horseshoe crabs and brachiopods.

it is a learned trait

explanation:

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs