University of Toronto (UofT) AST 101 The Sun and Its Neighbours Practice Exam

The key idea is using the predictable breakdown of unstable atomic nuclei to measure time. Radiometric dating relies on radioactive isotopes present in rocks. These isotopes decay into stable daughter isotopes at a constant rate, described by their half-lives. By measuring how much parent remains and how much daughter has formed, scientists calculate how long the decay has been happening, giving the rock’s age. This approach works well for rocks when minerals trap the parent isotope early and remain chemically closed afterward, so the measured ratio truly reflects time since formation.

Carbon dating is a form of radiometric dating but it targets organic materials and only works for relatively recent ages (up to tens of thousands of years), so it isn’t used for rocks. Dendrochronology uses tree rings for calendar years, not radioactive decay. Relative dating tells which rocks are older or younger but doesn’t yield an absolute age. Therefore, the method that uses radioactive decay to determine the age of rocks is radiometric dating.