Stratigraphy is the branch of geology that studies rock layers, or strata, to understand Earth's history. It involves analyzing the sequence, distribution, and age of these layers, which can reveal information about past environments, climate changes, and geological events. Geologists use stratigraphy to identify and date fossils, minerals, and other materials found within the layers. This helps in reconstructing the geological timeline and understanding processes like sedimentation and erosion. Key principles of stratigraphy include the Law of Superposition, which states that older layers are typically found below younger ones, and Lithostratigraphy, which focuses on the physical characteristics of rock layers.