The carbon-14 it contained at the time of death decays over a long period of time.
By measuring the amount of carbon-14 left in dead organic material the approximate time since it died can be worked out.
For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain.
Later called Ötzi the Iceman, small samples from his body were carbon dated by scientists.
These are released as radioactive particles (there are many types).
This decay process leads to a more balanced nucleus and when the number of protons and neutrons balance, the atom becomes stable.
This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
There's a small amount of radioactive carbon-14 in all living organisms.
When they die no new carbon-14 is taken in by the dead organism.
The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes.
Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.
This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.