The original radioactive atom is known as a parent isotope, while the atom produced by the decay process is known as a daughter isotope. For example Uranium-235 and Uranium-238 are both Uranium atoms with the same number of protons, but they have a different number of neutrons.The number used to identify the isotope refers to the total number of particles in the nucleus of each atom."Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure.We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess." [Rasmus Nyerup, (Danish antiquarian), 1802 (in Trigger, 19)].It has the same number of protons, otherwise it wouldn't be uranium.
All radioactive atoms decay to become a more stable kind of atom.Desmond Clark (1979) wrote that were it not for radiocarbon dating, "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation" (Clark, 1979:7).Writing of the European Upper Palaeolithic, Movius (1960) concluded that "time alone is the lens that can throw it into focus".Radioactive decay allows geologists and physicists to measure the age of ancient fossils, rocks and even the Earth.This process is called radiometric or radioactive dating.Renfrew (1973) called it 'the radiocarbon revolution' in describing its impact upon the human sciences.