Shellfish obtain carbon from the biosphere for shell building.
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From Wikipedia, the free encyclopedia. This effect causes the ages of samples to appear older than they actually are due to the incorporation of older CaCO3 that has been dissolved into the freshwater source from substances like limestone or marl that the lake or streams move through. Shells from both marine and land organisms consist almost entirely of calcium carbonate, either as aragonite or as calciteor some mixture of the two. How much does carbon dating cost? Either an acid etchsonication in alkali or no pretreatment. The outer layer of the shell is removed with a drill and carborundum paper to isolate aragonite—the analyte for AMS radiocarbon dating. Terrestrial shells, like snail shell, are also affected by the hard water effect in cases when the organism has been feeding on carbonate-rich areas like a chalkland.