All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.Elements exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.Contamination from outside, or the loss of isotopes at any time from the rock's original formation, would change the result.It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will spontaneously change into a different nuclide by radioactive decay.The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.It may be used to date a wide range of natural and man-made materials.Fossils may be dated by taking samples of rocks from above and below the fossil's original position.
This helps to counter the effects of heating and squeezing, which a rock may experience in its long history.
The amount of the isotope in the object is compared to the amount of the isotope's decay products.
Radiocarbon dating is one kind of radiometric dating, used for determining the age of organic remains that are less than 50,000 years old.
Among the best-known techniques are radiocarbon dating, potassium–argon dating and uranium–lead dating.
By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change.
For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms.