Knowing when the rock formed allows scientists to estimate a date for the fossils in the rock. Layers of sedimentary rock are called strata. Any fossils above a layer of strata are younger than that layer. Any fossils below are older than that layer. This means that older fossils and rocks are found in lower strata, deeper in the Earth. This idea is called the law of superposition. It is a key scientific principle in stratigraphy, which is a branch of science that deals with rock layers. What conclusion is BEST supported by the paragraph above?