What do geologist use to determine a rock's layers absolute age

The nuclear decay of radioactive isotopes is a process that behaves in a clock-like fashion and is thus a useful tool for determining the absolute age of rocks. Radioactive decay is the process by which a "parent" isotope changes into a "daughter" isotope.

Absolute Dating. The nuclear decay of radioactive isotopes is a process that behaves in a clock-like fashion and is thus a useful tool for determining the absolute age of rocks. Radioactive decay is the process by which a "parent" isotope changes into a "daughter" isotope.