What dating methods have been used to determine the age of the Earth?
Radioactive isotopes are those whose nuclei spontaneously decay, usually by emitting some neutrons or protons. The decaying radioactive isotope, or parent isotope, evolves into a decay product, the daughter isotope. Radioactive decay rates are constant, unaffected by changes in temperature, pressure or by chemical reactions involving the parent isotopes. The decay rate is characterized by the half-life of the parent, i.e. when X atoms of the parent decays into X/2 atoms of the parent, and X/2 atoms of the daughter. Different radioactive isotopes have different half-lives, and are useful for dating.
