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). Sedimentary rocks are normally laid down in order, one on top of another.
What purpose do geologists use relative dating?
Using a variety of methods, geologists are able to determine the age of geological materials to answer the question: how old is this fossil? Relative dating methods are used to describe a sequence of events. These methods use the principles of stratigraphy to place events recorded in rocks from oldest to youngest.
What can be determined using relative dating?
Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. estimated age).
Put simply, an unconformity is a break in time in an otherwise continuous rock record. Unconformities are a type of geologic contact—a boundary between rocks—caused by a period of erosion or a pause in sediment accumulation, followed by the deposition of sediments anew.
Recognition of unconformities is useful for subdividing stratigraphic units, determining the timing of tectonic activity, interpreting lateral facies relationships, constructing burial and uplift curves, correlating certain stratigraphic boundaries, interpreting sea-level changes, and for reconstructing paleogeography.