geochronologic

Geochronology is the science of determining the ages of rocks, minerals, fossils, and geological events. The adjective geochronologic is used to describe data, methods, or results associated with geochronology. Geochronologic information encompasses both absolute dating, which yields numerical ages, and relative dating, which orders events in time without specific ages.

Absolute dating relies on radioactive decay and other time-dependent processes. Common isotopic systems include uranium‑lead in zircon and other minerals, potassium‑argon and argon‑argon, rubidium‑strontium, and samarium‑neodymium. Radiocarbon dating (carbon-14) is widely used for relatively young materials up to about 50,000 years old. Additional geochronologic methods include luminescence dating (thermoluminescence and optically stimulated luminescence), fission-track dating, and cosmogenic nuclide dating, which harness the production of isotopes by cosmic rays. Relative dating methods, often used for stratigraphic sequences, include biostratigraphy, magnetostratigraphy, and sequence dating through fossil assemblages and rock relationships.

The results contribute to the geochronologic timescale, which organizes Earth history into units such as eons, eras, periods, epochs, and ages. Data interpretation frequently uses tools like isochrons, concordia diagrams, and knowledge of closure temperatures to ensure consistency across multiple dating systems.

Applications span understanding the timing of plate tectonics, volcanism, climate shifts, sedimentation, and mass extinctions. Limitations include uncertainties in measurement, sample contamination, diagenetic alteration, and the need for suitable minerals. Geochronology remains essential for reconstructing the chronology of Earth’s history and its geological processes.