Radiogenic dating methods
U-238 decays to Pb-206, and U-235 decays to Pb-207.These two decay pathways have different half-lives that have been measured and recorded.Carbon-14 has two more neutrons than stable carbon, and thus has a mass that is greater by two.Carbon-14 is produced by a chemical reaction between stable Nitrogen atoms or ions and free neutrons in the atmosphere.It is especially disposed to dating minerals such as Zircon.Zircon is a fairly abundant mineral that exists in many forms in the environment, and because of its chemical structure Uranium is easily incorporated into its molecules.
 While radiocarbon dating is very useful in cases where organic matter is being analyzed, in many cases the samples that are being dated were never alive.
One of the primary decay products of K-40 is Ar-40--a stable and unreactive gas.
Potassium decay has been established as the only source of Argon in volcanic rocks; it is a gas so most of it escapes unless it is formed after the molten rock has solidified, and it is not a major product in any other reactions.
This means that if the amounts of C-14 and N-14 in a sample are known, then its age can be calculated for a wide range of years.
Several half-lives can pass and still leave measurable amounts radioactive carbon present in the sample.