All living things are built of carbon atoms. There are various isotopes, or species, of carbon atoms with the same atomic number but different mass.
One radioactive, or unstable, carbon isotope is C14, which decays over time and therefore provides scientists with a kind of clock for measuring the age of organic material.
While alive, all plants and animals take C14 into their bodies. The numbers of C14 atoms and non-radioactive carbon atoms remain approximately the same over time during the organism’s life. As soon as a plant or animal dies, the carbon uptake stops. The radioactive carbon isotope is no longer replenished; it only decays.
Scientists have calculated the rate at which C14 decays. By measuring how much C14 remains in a sample of organic material, we can estimate its age within a range of dates.
