Radiometric dating is also referred to as radioactive dating. It is a way to know the age of materials such as rocks and carbon. In order to know the age of a rock or carbon, a comparison of the radioactive isotope to its accepted presence, and rate of decay is determined. The mass spectrometer aids geologists to know the age of rocks and carbon. Relative dating, on the other hand, is a way to know the age of one rock from the other or what we call the geologic event of a rock. This is a determination of the year when the rocks was formed.