Why do sedimentary layers usually form in bands?

Sedimentary rocks form when particles such as sand, silt, clay, or shell fragments settle out of water, air, or ice and are later compacted and cemented. Because deposition happens step by step, the result is often visible layering called stratification. Each layer can reflect a different environment, such as a river flood, a desert dune, or a quiet lakebed. Geologists use these layers to reconstruct Earth’s past because lower layers are generally older than higher ones, a principle known as superposition. Famous sedimentary sequences preserve fossils, ancient climates, and even past sea levels.