Carbon 14 is formed from the collision between cosmic rays and nitrogen 14, found in the Earth’s atmosphere.
This carbon isotope easily bonds with oxygen, forming carbon dioxide (14CO2), which is absorbed by plants. When a living being dies, the amount of carbon 14 decreases, which implies radioactive decay.
The half-life of carbon 14 (14C) is 5730 years. This means that if an organism died 5730 years ago it will have half the 14C content.
The half-life of a radioisotope element is the time required for it to disintegrate to half its mass, which can occur in seconds or billions of years, depending on the degree of intensity of the radioisotope. That is, if we have 200 g of mass of a radioactive element, whose half-life is 10 years, after these 10 years the element will have 100 g of mass. Therefore, the radiocarbon age of the fossil sample can be obtained by comparing the specific radioactivity 14C/12C of this sample. In this case, the lower the amount of carbon 14 found in the sample, the older it is.
To find out how long ago an organism died, the amount of electrons that the organism emitted per minute per gram of material is determined, which today is approximately 15 electrons emitted per minute per gram of sample.