As Dalrymple (1994) points out, available techniques give us more than the accuracy we need. How can we figure out the amount of the daughter element originally present?
Hence, in the case of these minerals, we can conclude that no argon was originally present; that is, D = 0.
Given this value of Dit is then possible to use either decay process to calculate the age of the rock.
If the results agree, they are said to be concordant, and geologists are usually confident that concordant ages are the true ages of the rocks under consideration.
A second, independent, astronomical method is to use standard techniques to measure some parameters of stars (mass, luminosity, compositor, and surface temperature), from which a well-confirmed theory of the life histories of stars enables physicists to compute their. Finally, considerations of radioactive decay make it possible to calculate the time at which certain heavy elements were formed.
These techniques are somewhat similar to the radiometric methods of dating rocks, which I shad consider in a little more detail.
(For an excellent overview of the various ways of assigning an age to the universe, and an exposition of the radioactive decay method, see Schramm 1974.)Although the clear consensus of physical techniques is that the universe is billions of years old, and although this result controverts the claims of at least some contemporary Creationists, the principal Creationist attack has been directed against the standard geological claim that the earth is about 4.5 billion years old.