Uranium lead dating method
These long time periods are computed by measuring the ratio of daughter to parent substance in a rock and inferring an age based on this ratio.
This age is computed under the assumption that the parent substance (say, uranium) gradually decays to the daughter substance (say, lead), so the higher the ratio of lead to uranium, the older the rock must be.
To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating.
Radiometric dating is largely done on rock that has formed from solidified lava.
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.
The general idea is that many different minerals are formed, which differ from one another in composition, even though they come from the same magma.
For this reason, this arrangement of minerals became known as Bowen's reaction series.
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.
But at the same time, it will be enriched in the elements contained in the later forming minerals, namely sodium and potassium.
Further, the silicon content of the melt becomes enriched toward the latter stages of crystallization.