Isotopic Replacement

A chemical process which creates inaccuracies in radiocarbon/radiometric dating. An isotope within a sample is exchanged with an isotope of the same element that is a different age. This can occur in fossil shells whose C14 isotope in the calcium carbonate may be replaced during recrystallization by different carbon isotopes dissolved in the surrounding groundwater.

Source of inaccuracy when determining radiocarbon dates from fossil shells. If the ancient material has been buried in sediments subject to percolation of modem rainwater, there may be some interchange of carbon between the calcium carbonate of the shell and the carbon dioxide dissolved in the rainwater. This introduces a quantity of ‘young’ carbon, rich in the 14C isotope, and can make the date appear to be younger than it is. See hard water effect.