Rating and dating definition
Because of the carbon cycle, there is always carbon-14 present in both the air and in living organisms.
Scientists often use the value of 10 half-lives to indicate when a radioactive isotope will be gone, or rather, when a very negligible amount is still left.
Once they die, they stop taking in carbon-14, and the amount present starts to decrease at a constant half-life rate.
Then the radiocarbon dating measures remaining radioactivity.
Radiocarbon dating is a method used to date materials that once exchanged carbon dioxide with the atmosphere; in other words, things that were living.
Carbon-14 is a radioactive isotope and is present in all living things in a constant amount.