Of course, there are many problems with such dating methods, such as parent or daughter substances entering or leaving the rock, as well as daughter product being present at the beginning.
Here I want to concentrate on another source of error, namely, processes that take place within magma chambers.
Most scientists today believe that life has existed on the earth for billions of years.
This belief in long ages for the earth and the existence of life is derived largely from radiometric dating.
For example, at the stage when about 50 percent of the magma has solidified, the melt will be greatly depleted in iron, magnesium, and calcium, because these elements are found in the earliest formed minerals.Oftentimes the rate of cooling occurs rapidly enough to prohibit the complete transformation of calcium-rich feldspar into sodium-rich feldspar.In these instances, the feldspar crystals will have calcium-rich interiors surrounded by zones that are progressively richer in sodium.On the upper left branch of this reaction series, olivine, the first mineral to form, Ml] react with the remaining melt to become pyroxene.This reaction will continue until the last mineral in the series, biotite mica, is formed.Ordinarily, these reactions are not complete so that various amounts of each of these minerals may exist at any given time.