For example, earthquakes occur along faults. Scientists can determine the location of fault lines so we don't build our houses along the lines. Also, lighthouses built along coasts centuries ago are being moved today because rock cliffs between them and the ocean have eroded away. Earthquakes, volcanic activity, and floods are not new. These things have been happening for years and years.
Scientists also study rocks to learn about the history of the natural world.
Animals that existed millions of years or even just hundreds of years ago aren't around today. An example is a Dodo bird. Dodo birds were hunted to extinction, but there are other animals, like dinosaurs, that are extinct for other reasons. By studying the fossils of these animals, scientists can try to determine what the animal looked like when it was alive, what types of food it ate, how it died, and why it became extinct. Sedimentary rocks are made up of layers of silt, small pieces of other rocks, and sometimes the skeletons of tiny creatures.