Final answer:
Relative age is determined by the sequence of events or the position of fossils in rock layers, while absolute age is measured in years and is determined by measuring isotopic decay.
Step-by-step explanation:
Relative age refers to the geologic age of an organism, rock, or event that is defined in relation to other rocks or events rather than in years before present or an absolute age. It is determined by the sequence of events or the position of fossils in rock layers. For example, lower layers are assumed to contain older fossils than higher layers.
Absolute age, on the other hand, is measured in years and is usually determined by measuring isotopic decay. It provides an exact numerical age for a rock or mineral. Geologists use radioactive isotopes to determine the absolute age of a rock.