The law of superposition is used for dating rock, sediment and strata deposits.
The law of superposition has to do with layers of ground and their age. The law, itself, provides a method of determining the age of each ground layer in a given geological location.
The law of superposition states that in any given collection of sediment or rock left undisturbed, the youngest layer is the top layer and the oldest is the bottom. For example, if a layer of mudstone is directly atop a layer of basalt, the basalt is the older of the two layers.
The law of superposition is the foundation and guiding principle of stratigraphy, the study of geological layers of earth and soil. This scientific field provides the most accurate archaeological method for relatively figuring out the age of an archeological site.
While this is a fairly accurate method for dating ground layers, it’s not foolproof. For example, erosion can cause a specific ground layer to deteriorate, making it harder to accurately read. Similarly, if any period of time passes without sediment development, it may make determining layer age more difficult.