As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged.Carbon-14 is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere.
(crit) Thought to have been evidence for common ancestry until significant advancements were made in biochemistry.When granite rock hardens, it freezes radioactive elements in place.The most common radioactive element in granite is Uranium-238.Simply put, "Similarity does not imply a genetic relationship." (Dr. 290.) Evidence for Evolution - Embryology: (ex) Embryos of different vertebrates look alike in their early stages, giving the superficial appearance of relationship.(crit) Embryos of different vertebrates DO NOT look alike in their early stages.