A central insight of geology is deep time, the knowledge that rocks we can pick up and hold formed millionsno, billions of years ago. On other planets, it's routine to find not just rocks, but surfaces that have sat there undisturbed for over a billion years. Those planets don't have rain, or seas, or plate tectonics, though, so surely Earth can't match them. But Earth also has places that are very old indeed, where you can stand in the same landscape that existed in previous geologic periods. Let me introduce you to five of them.