alpha-helium radioactive clock

The alpha-helium radioactive clock is a method for determining the age of minerals and rocks. It relies on the accumulation of helium, which is produced during the radioactive decay of uranium-235, uranium-238, and thorium-232. Alpha particles, which are helium nuclei, are emitted during this decay process.12

The ratio of helium to its radioactive parent isotopes in a mineral or rock can serve as a measure of geologic time. While this method was historically important for establishing early geologic time scales, helium can escape from rocks, often leading to ages that are too low. However, it may prove useful for dating younger rocks and minerals, as they are less likely to have experienced complex thermal histories that would cause helium loss. Fossils can also be dated using this technique.1