What is the term for the age of a rock layer in relation to other rock layers?

The age of a rock layer in relation to other rock layers is referred to as relative age. This concept is a fundamental principle in geology that allows scientists to determine the chronological order of rock formations and the events that shaped them, without necessarily knowing their exact age in years. Relative dating methods consider the geological principles of superposition, original horizontality, and cross-cutting relationships to establish which layers are older or younger compared to others.

For example, if a layer of sedimentary rock is found above another, the one on top is inferred to be younger than the one below it. Relative age does not provide a specific numerical age; instead, it places geological events in a sequence, which is crucial for understanding the history of the Earth's surface.

The other terms refer to different aspects of geology. Absolute age measures the actual age of a rock layer in years, typically through methods like radiometric dating. Geochronology is the science of determining the age of rocks, fossils, and sediments, often using both relative and absolute dating. Radiometric dating specifically involves measuring the decay of isotopes to determine the age of materials, but it does not pertain to their relative positioning or relationship to each other.