Primate Origins and the Plesiadapiforms. Relative age dating also means paying attention to crosscutting relationships. The Earth's magnetic field has reversed many times during its history. But with the relative dating without necessarily determining when. In an undeformed sequence, the oldest rocks are at the bottom and the youngest rocks are at the top. A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.