radiometric dating

A way to determine how old geologic materials are, in years, based on how much of a radioactive isotope, such as Carbon-14, is present. Isotopes are elements that belong to the same family on the Periodic Table because they have the same number of protons (that is, positively charged subparticles) but different numbers of neutrons (that is, subparticles with no charge). The “parent” isotope decays over time into a “daughter” isotope at a consistent rate, and geologists measure the ratio of parent-to-daughter to determine the age of rocks and other materials. The potassium-argon method is often used in radiometric dating.