Editing Age of Earth (section)

===Overview===
By their chemical nature, [[Rock (geology)|rock]] [[mineral]]s contain certain [[Chemical element|elements]] and not others; but in rocks containing radioactive isotopes, the process of [[radioactive decay]] generates exotic elements over time. By measuring the [[concentration]] of the stable end product of the decay, coupled with knowledge of the [[half life]] and initial concentration of the decaying element, the age of the rock can be calculated.<ref name=nichols>{{cite book | author=Nichols, Gary | title=Sedimentology and Stratigraphy | chapter=21.2 Radiometric Dating | pages=325–327 | publisher=John Wiley & Sons | date=2009 | isbn=978-1405193795}}</ref> Typical radioactive end products are [[argon]] from decay of [[potassium]]-40, and [[lead]] from decay of [[uranium]] and [[thorium]].<ref name=nichols/> If the rock becomes molten, as happens in Earth's [[Mantle (geology)|mantle]], such nonradioactive end products typically escape or are redistributed.<ref name=nichols/> Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than Earth itself.