Dendrochronology relative dating method
From the results of studies on the origins of the various kinds of rocks (petrology), coupled with studies of rock layering (stratigraphy) and the fossils they contain (paleontology), geologists have associated layers of rocks with sequence of events thought to have occurred over hundreds of millions of years.
Some types of relative dating techniques include climate chronology, dendrochronology, ice core sampling, stratigraphy, and seriation.
Between the years of 17, James Hutton and William Smith advanced the concept of relative dating.
William Smith's collecting and cataloging fossil shells from rocks led to the discovery that certain layers contained fossils unlike those in other layers (see: fossil sorting).
Using these key or index fossils as markers, geologists began to identify a particular layer of rock wherever it was exposed.