Radiometric age dating
Carbon-14 is present a level of about 1 part per trillion in the atmosphere--for every trillion particles of carbon one is C-14.
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.
However, Lead is not easily incorporated into the Zircon molecules; therefore, when a sample of Zircon is analyzed any lead that is found must have come directly from Uranium decay.
There are two isotopes of Uranium, both of which are radioactive.
Depending on what is being dated (what it is composed of, where it resides) some methods will be more effective than others.
On this page, you will find descriptions of several of the most popular and useful methods that exist today.
Search for radiometric age dating:
Since C-14 is formed in the atmosphere, it is most abundant in CO2 in the atmosphere.