Minerals Used in Shells
Small shelly fossils are composed of a variety of minerals, the most important being silica, calcium phosphate and calcium carbonate. The minerals used by each organism are influenced by the chemistry of the oceans the organism first evolved in, but then continue to be used even if the ocean chemistry changes. For example in the Ediacaran period and the Nemakit-Daldynian age of the Cambrian, those animals that used calcium carbonate used the form called aragonite. On the other hand animals that first appeared in the following Tommotian age used another form, calcite.
A recently-discovered modern gastropod that lives near deep-sea hydrothermal vents illustrates the influence of both earlier and contemporary local chemical environments: its shell is made of aragonite, which is found in the earliest fossil molluscs; but it also has armor plates on the sides of its foot, and these are mineralized with the iron sulfides pyrite and greigite, which had never previously been found in any metazoan but whose ingredients are emitted in large quantities by the vents.
Methods of constructing shells vary widely among the SSF, and in most cases the exact mechanisms are not known.
Read more about this topic: Small Shelly Fauna
Famous quotes containing the word shells:
“It is not easy to make our lives respectable by any course of activity. We must repeatedly withdraw into our shells of thought, like the tortoise, somewhat helplessly; yet there is more than philosophy in that.”
—Henry David Thoreau (1817–1862)