40Ar/39Ar

The 40Ar/39Ar dating method measures the age of rocks by analyzing the ratio of two argon isotopes. When rocks containing potassium are heated or exposed to radiation, potassium-39 is converted into argon-39, serving as a reference. Over time, potassium-40 in the rock decays into argon-40. By comparing the amounts of argon-40 and argon-39, scientists determine how long ago the rock formed or last cooled below a certain temperature. This technique is valuable for dating volcanic and igneous rocks, helping understand Earth's history and geological processes.