Relative dating is the process of determining if one rock or geologic event is older or younger than another, without knowing their specific ages—i. The principles of relative time are simple, even obvious now, but were not generally accepted by scholars until the scientific revolution of the 17th and 18th centuries [ 3 ]. James Hutton see Chapter 1 realized geologic processes are slow and his ideas on uniformitarianism i. Stratigraphy is the study of layered sedimentary rocks. This section discusses principles of relative time used in all of geology, but are especially useful in stratigraphy.
This is an example of a relative age diagram. It is a cross-section through the Earth. Relative age diagrams can include rock layers, intrusions, unconformities, and geologic structures folds and faults. In the diagram above, A, B , and C are sedimentary rocks. D is an igneous rock. There are somewhat standard symbols to indicate different categories of rocks.
The process of elements breaking down, or decaying, over time and releasing particles and elements. This scale is a record of the geological events and the evolution of life forms as shown in the fossil record. This type of fossil forms when dissolved minerals replace the remains of an organism and then harden to form rock. The age of a rock categorized by the number of years that have passed since the rock has formed.
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence. The method of reading the order is called stratigraphy layers of rock are called strata. Relative dating does not provide actual numerical dates for the rocks.