So far, we have learned how to sequence geologic events and structures in a given area, such as the Grand Canyon. It is often valuable to know how events in one given area relate to events in another area- or even another continent. It is sometimes very difficult to trace rocks unambiguously from one area to another, and seemingly impossible to do so across an ocean. Nature has provided us with yet another set of clues that we can use to do this- fossils. Fossils are the remains or traces of once living organisms. Photo is of a dinosaur footprint near Tuba City Arizona.