Dating very old rocks
The mineral makeup of an igneous rock is ultimately determined by the chemical composition of the magma from which it crystallized.
Such a large variety of igneous rocks exists that it is logical to assume an equally large variety of magmas must also exist.
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Most scientists today believe that life has existed on the earth for billions of years.
Here I want to concentrate on another source of error, namely, processes that take place within magma chambers.
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.
Bowen also demonstrated that if a mineral remained in the melt after it had crystallized, it would react with the remaining melt and produce the next mineral in the sequence shown in Figure 3.6.
55-57, (1987), gives us an idea of the tremendous complexity of the processes that occur when magma solidifies.
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.
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.
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.