what is stratigraphy

Stratigraphy is a branch of geology that deals with the study of rock layers (strata) and layering (stratification) . It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age) . The basic concept in stratigraphy is the law of superposition, which states that in an undeformed stratigraphic sequence, the oldest rocks will be found at the bottom and the youngest rock will be found at the top. Stratigraphers grapple with a record that was incomplete to begin with, and is further reduced over geologic time. Still, the remaining story these layers of sediment have to tell is powerful and important. Stratigraphy allows us to relatively date each layer of soil based on the artifacts found in each stratum, which helps us understand the history of our planet, including our own home landscape. Stratigraphy is also important in fields such as petroleum geology and archaeology.