Radiometric dating is also used to date archaeological materials, including ancient artifacts.
Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.
This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclide(s) into a material to the present.
The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation.
Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample.
It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.
(For some nuclides which decay by the process of electron capture, such as beryllium-7, strontium-85, and zirconium-89, the decay rate may be slightly affected by local electron density, therefore these isotopes may not be as suitable for radiometric dating.) But in general, the half-life of any nuclide is essentially a constant.