Geochronology

Geochronology determines the numerical ages and chronological order of rocks, minerals, geological events, and episodes in Earth’s history.

Radiometric dating: A method of calculating age from predictable changes in radioactive isotopes and their decay products. Radioactive decay provides many of geochronology’s most precise numerical ages.
Radioactive decay: The spontaneous transformation of unstable atomic nuclei into more stable nuclei, releasing particles or energy. This physical process supplies the clocks used in radiometric dating.
Uranium–lead dating: A radiometric method using uranium decay to lead to date zircon and other uranium-bearing minerals. It is widely used to date Earth’s oldest rocks and constrain crustal history.
Relative dating: A method that places rocks or events in sequence without assigning numerical ages. It establishes older-than and younger-than relations where absolute dates are absent.
Isotope system: A parent isotope and its radioactive daughter isotopes, considered together for dating or tracing geological processes. Each isotope system records time across particular minerals and geological conditions.
Isotope: One of two or more forms of an element whose atoms have different numbers of neutrons. Dating depends on distinguishing parent and daughter isotopes of the same elements.
Potassium–argon dating: A radiometric method that dates minerals and rocks through the decay of potassium-40 to argon-40. It dates volcanic materials that help bracket fossils and archaeological sites.
Luminescence dating: A method estimating when mineral grains were last exposed to sunlight or sufficient heat. It dates sediment deposition or heating rather than the crystallization of its minerals.
Half-life: The time required for half the atoms of a radioactive isotope in a sample to decay. Known half-lives let geochronologists convert isotope ratios into elapsed time.
Zircon: A durable mineral that incorporates uranium while excluding most lead when it crystallizes. Its uranium-lead record can preserve the age of ancient geological events.

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