Friday, January 27, 2012

How do shells in the ocean form, and how long can the last?

Shells are formed by living organisms. The ones that are most familiar are formed by bivalves (clams, oysters) and gastropods (snails). Other that you might see on a beach are echinoderms, such as sand dollars or sea urchins. Quite a few other marine organisms build shells as well.



Shell making organisms, such as brachiopods have been around for about 500-570 million years. I have a few shells that are that old. While they are fossils, they contain much of the original material that was in the shell. Over time the organic materials that give shells color and create the layers known as nacre (mother-of-pearl) are gone, but some of the original calcium carbonate remains, and the shells are recognizable as their original shape and form. Parts of a shell that have been deposited by the original organism as aragonite may change over time to calcite, but the chemical formula for calcite and aragonite are identical (CaCO3). The crystal structure is the only difference between the two.



Shells are actually made by a special tissue within organisms that secrete shells, and recent work has revealed that blood cells also play a part in the process by transporting tiny crystals of calcium carbonate to the site of shell-making within the organism.

See:

http://sciencenow.sciencemag.org/cgi/con...

The source of the calcium carbonate is from the water that these organism live within.

How do shells in the ocean form, and how long can the last?
The "critter" that lives in the shell, except for the hermit crab, makes their shells. They secrete the material, usually a calcium based material, which forms the shell. Those shells can last for centuries if not attacked by something able to destroy the shell material, such as an acid.
Reply:The oysters and all those shell fish make their own as they grow.

The shells will last for years, long after the occupants have died of old age or have been eaten by those of us in the deep depths.

I have walked on beaches made up of broken shells thrown up from the ocean/


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