Contamination from outside, or the loss of isotopes at any time from the rock's original formation, would change the result.
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.
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.
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 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.
Radiometric dating is also used to date archaeological materials, including ancient artifacts.
Radiometric dating methods are used to establish the geological time scale.
Plotting an isochron (straight-line graph) is used to solve the age equation graphically.
It shows the age of the sample, and the original composition.