The reason this age may not be a true age—even though it is commonly called an absolute age—is that it is based on several crucial assumptions.Most radiometric dating techniques must make three assumptions: The major problem with the first assumption is that there is no way to prove that the decay rate was not different at some point in the past.
Certain types of rocks, especially those that form from magma (igneous), contain radioactive isotopes of different elements.
The starting isotope is called the parent and the end-product is called the daughter.
The time it takes for one half of the parent atoms to decay to the daughter atoms is called the half-life.
Some of the common isotope pairs used are K-Ar, Rb-Sr, Pb-Pb, and U-Pb.
Carbon-14 dating is another common technique, but it can only be used on carbon-containing things that were once alive.