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.
Radiometric dating is also used to date archaeological materials, including ancient artifacts.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.
Scientists look at half-life decay rates of radioactive isotopes to estimate when a particular atom might decay.
It is therefore said to be 'fissile' and we use the expression 'nuclear fission'.