Radiometric Dating - The Assumptions Many of the ages derived by radiometric dating techniques are highly publicized.Nevertheless, the fundamental assumptions employed are not.Although no convincing argument for a change in the speed of light over time has been made, the question is irrelevant to the validity of tree-ring calibrated radiocarbon dates.As with variation in atmospheric radiocarbon concentration, the decay rate of radiocarbon in tree-ring calibration samples would be affected in exactly the same way as the decay rate of radiocarbon in the specimen to be dated.Radiometric Dating - A Brief Explanation Radiometric dating is the primary dating scheme employed by scientists to determine the age of the earth.Radiometric dating techniques take advantage of the natural decay of radioisotopes.The Uranium-238 radioisotope goes through 13 transitional stages before stabilizing into Lead-206 (U238 Pb206).In this instance, Uranium-238 is called the "parent" and Lead-206 is called the "daughter".
(This is consistent with the geologic 'age' assigned to the granites in which these zircons are found.) There is a significant amount of helium from that '1.5 billion years of decay' still inside the zircons.
Dr Carl Wieland summarizes the recent findings: "When uranium decays to lead, a by-product of this process is the formation of helium, a very light, inert gas which readily escapes from rock.
Certain crystals called zircons, obtained from drilling into very deep granites, contain uranium which has partly decayed into lead.
An isotope is one of two or more atoms which have the same number of protons in their nuclei, but a different number of neutrons.
Radioisotopes are unstable isotopes: they spontaneously decay (emitting radiation in the process -- thus making them radioactive).