How did radioactive decay help scientists estimate the age of rocks?

Radioactive decay allows scientists to estimate the age of rocks through a process known as radiometric dating. This method relies on the fact that radioactive isotopes (parent atoms) decay into stable daughter atoms at a constant, immutable rate, characterized by a specific half-life.12

By measuring the ratio of parent isotopes to daughter isotopes within a rock or mineral sample, scientists can calculate the time elapsed since the material formed. As time passes, the number of parent atoms decreases while the number of daughter atoms increases; therefore, a higher daughter-to-parent ratio indicates an older sample.12

This application of physics to geology was significantly advanced by Ernest Rutherford, who developed the transformation theory of radioactivity. Following his suggestion, Bertram Borden Boltwood used the accumulation of lead—the stable end product of uranium decay—to demonstrate that certain rocks were billions of years old, fundamentally changing our understanding of geologic time.3