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.
There are certain kinds of atoms in nature that are unstable and spontaneously change (decay) into other kinds of atoms.
For example, uranium will radioactively decay through a series of steps until it becomes the stable element lead. The original element is referred to as the parent element (in these cases uranium and potassium), and the end result is called the daughter element (lead and argon).
This feature is produced by changes in deposition over time.
With this in mind geologist have long known that the deeper a sedimentary rock layer is the older it is, but how old?
This apparent consistency in textbooks and the media has convinced many Christians to accept an old earth (4.6 billion years old).