Radiometric dating is largely done on rock that has formed from solidified lava.
However, geologists have found that various eruptive stages of the same volcano often extrude lavas exhibiting somewhat different mineral compositions, particularly if an extensive period of time separated the eruptions.
Evidence of this type led them to look into the possibility that a single magma might produce rocks of varying mineral content. Bowen discovered that as magma cools in the laboratory, certain minerals crystallize first.
This calls the whole radiometric dating scheme into serious question.
Geologists assert that older dates are found deeper down in the geologic column, which they take as evidence that radiometric dating is giving true ages, since it is apparent that rocks that are deeper must be older.
A pioneering investigation into the crystallization of magma was carried out by N. At successively lower temperature, other minerals begin to crystallize as shown in Figure 3.6.
As the crystallization process continues, the composition of the melt (liquid portion of a magma, excluding any solid material continually changes.This chapter provides researchers with a guide to some of the types of dating techniques that can be used in geomorpological investigations and issues that need to be addressed when using gechronological data, specifically issues relating to accuracy and precision.This chapter also introduces the 'types' of dating methods that are commonly used in geomorphological studies.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.This includes sidereal, isotopic, radiogenic, and chemical dating methods. These databases contain citations from different subsets of available publications and different time periods and thus the citation count from each is usually different.