Radiocarbon decays slowly in a living organism, and the amount lost is continually replenished as long as the organism takes in air or food. Because carbon-14 decays at this constant rate, an estimate of the date at which an organism died can be made by measuring the amount of its residual radiocarbon.

Why do we use carbon dating to calculate the age of fossils?

In this section we will explore the use of carbon dating to determine the age of fossil remains. Therefore, by knowing the amount of 14C in fossil remains, you can determine how long ago an organism died by examining the departure of the observed 12C to 14C ratio from the expected ratio for a living organism.