A geological layer, also known as a stratum, is a distinct layer of rock or sediment that has formed over time. These layers are created by various geological processes, such as sedimentation, volcanic activity, and erosion. Each layer can provide valuable information about the Earth's history, including changes in climate, environment, and biological evolution. Geologists study these layers to understand the Earth's structure and the processes that shaped it. By examining the composition, thickness, and fossil content of each layer, scientists can reconstruct past environments and make predictions about future geological changes. This study often involves related topics like paleontology and stratigraphy.