地層學是地學的核心學科。了解巖石單元的排列順序是了解感興趣地區地質歷史的關鍵。地球科學家的一項共同任務是尋找某一巖石單位的地層背景資料，例如它的年齡、性質及其在地層單位層次結構中的位置。

Stratigraphy is a core discipline of the geological sciences. Understanding the order in which units of rock were emplaced is the key to understanding the geological history of an area of interest. A common task for earth scientists is the search for stratigraphic background information on a certain rock unit, e.g. its age and properties and its position within the hierarchy of stratigraphic units.