Radiometric dating (often called radioactive dating) is a way to find out how old something is.
The method compares the amount of a naturally occurring radioactive isotope and its decay products, in samples. It is the main way to learn the age of rocks and other geological features, including the age of the Earth itself.
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.
The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.The method works best if neither the parent nuclide nor the daughter product enters or leaves the material after its formation.Anything which changes the relative amounts of the two isotopes (original and daughter) must be noted, and avoided if possible.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.Measurements should be taken on samples from different parts of the rock body.This helps to counter the effects of heating and squeezing, which a rock may experience in its long history.Different dating methods may be needed to confirm the age of a sample.For example, a study of the Amitsoq gneisses from western Greenland used five different radiometric dating methods to examine twelve samples and got agreement to within 30 million years on an age of 3,640my.Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.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.