it matches what they already believe on other grounds. A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.
It may be surprising to learn that evolutionary geologists themselves will not accept a radiometric date unless they think it is correct—i.e. So, how do geologists know how to interpret their radiometric dates and what the ‘correct’ date should be?
From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events.
It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place.
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.
For example, a geologist may examine a cutting where the rocks appear as shown in Figure 1.
Here he can see that some curved sedimentary rocks have been cut vertically by a sheet of volcanic rock called a dyke.