What is the term for the actual age of geological materials, usually measured in years?

The term that refers to the actual age of geological materials, measured in years, is absolute time. This concept is fundamental in geology, as it allows scientists to determine the precise age of rock formations, fossils, or other geological events using various dating methods. Absolute time provides a quantitative measurement that can be used to establish a timeline of Earth's history or the life span of geological features.

In contrast, radiometric dating is a method used to determine absolute time by measuring the decay of radioactive isotopes in materials, but the term itself specifically refers to the technique rather than the concept of measuring age. Relative time, on the other hand, refers to the chronological sequence of geological events without assigning actual dates, focusing instead on the order in which events occurred. Superposition is a principle used in relative dating that states younger layers of rock are deposited on top of older layers; it does not provide actual age measurements but rather helps establish a sequence of events. Thus, absolute time is the best term to represent the actual numerical age of geological materials.