Scientific definition of carbon dating
By measuring the amount of carbon-14 left in the organism, it's possible to work out how old it is.
This technique works well for materials up to around 50,000 years old.
This is why radiocarbon dating is only useful for dating objects up to around 50,000 years old (about 10 half-lives).
Carbon-14 has a half-life of 5,730 ± 40 years—, half the amount of the radioisotope present at any given time will undergo spontaneous disintegration during the succeeding 5,730 years. It has proved to be a versatile technique of dating fossils and archaeological specimens from 500 to 50,000 years old.
Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms.