On the Validity of Radiocarbon Dates from Snail Shells

The use of snail shells for dating Pleistocene events by the C¹⁴ method has been questioned. If snails in some manner incorporate into their shells the C¹⁴-free carbonate of the limestone in their environment, C¹⁴ dates derived from these "diluted" shells would appear too old. The uptake of inorganic carbon in snail shell matter was measured by feeding C¹⁴-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 C¹⁴ date of approximately one thousand years.