On the Validity of Radiocarbon Dates from Snail Shells

The use of snail shells for dating Pleistocene events by the C^14 method has been questioned. If snails in some manner incorporate into their shells the C^14-free carbonate of the limestone in their environment, C^14 dates derived from these "diluted" shells would appear too old. The uptake of inorganic carbon in snail shell matter was measured by feeding C^14-labeled CaCO₃ to aquatic and terrestrial snails. The activity of the new shell growth indicates that 10-12 per cent uptake is possible, yielding an uncertainty in the C^14 date of approximately one thousand years.