Both Carbon-12 and Carbon-13 are stable, but Carbon-14 decays by very weak beta decay to nitrogen-14 with a half-life of approximately 5,730 years.
After the organism dies it stops taking in new carbon.
It is naturally radioactive and unstable, and will therefore spontaneously decay back into N-14 over a period of time.
This property makes it especially useful in a process known as “radiocarbon dating”, or carbon dating for short.
By measuring the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of the artifact.
Here on Earth, Carbon is found in the atmosphere, the soil, the oceans, and in every living creature. C-12, so-named because it has an atomic weight of 12 – is the most common isotope, but it is by no means the only one.
Carbon 14 is another, an isotope of carbon that is produced when Nitrogen (N-14) is bombarded by cosmic radiation.
This process causes a proton to be displaced by a neutron, effectively turning atoms of Nitrogen it into an isotope of carbon – known as”radiocarbon”.
Animals and people take in carbon-14 by eating the plants.The ratio of normal carbon (carbon-12) to carbon-14 in the air and in all living things at any given time is nearly constant.Maybe one in a trillion carbon atoms are carbon-14.When these energetic neutrons collide with a nitrogen-14 (seven protons, seven neutrons) atom it turns into a carbon-14 atom (six protons, eight neutrons) and a hydrogen atom (one proton, zero neutrons).Since Nitrogen gas makes up about 78 percent of the Earth's air, by volume, a considerable amount of Carbon-14 is produced.