Sedimentary rocks are formed from particles and materials that settle over time. These materials can include bits of sand, clay, and even fossils from ancient plants and animals. As layers of these sediments build up, they become compacted and cemented together, creating solid rock. This process often takes thousands to millions of years. One common example of sedimentary rock is limestone, which is primarily made from the remains of marine organisms. Sedimentary rocks are important because they can hold valuable resources like coal and oil, and they also provide clues about Earth's history, including past climates and environments.