The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes.Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.
But if they are earlier than 1485, then they can’t be Richard’s remains.Fossil fuels like coal and oil have been around for so long — millions of years — that all of their carbon-14, which has a half life of 5,730 years, is already decayed and gone.A half life is the period of time that it takes half a sample to decay.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.those that form during chemical reactions without breaking down).