This is based on the concept that, in a normal depositionary sequence, the deepest layers are also the oldest.
The age determined by relative dating is based on the rules of super imposition and the presumed age of strata based on fossils.“Relative Dating.” Science Learning Hub, Available Here 1. “Radiocarbon Date Calibration Curve” By Howard Morland – Own work based on information from: Reimer, P. Absolute age is a quantitative measurement while relative age is a qualitative measurement.
Absolute dating works better for igneous and metamorphic rocks while relative dating works better for sedimentary rocks having layered arrangement of sediments.
Relative dating is based on super imposition and fossils.