geochronology

Geochronology is the science of determining the ages of rocks, minerals, fossils, and the timing of geological events. It uses natural clocks contained in minerals and sediments to establish a timeline for Earth's history. The central goal is to assign numerical ages to features and to place them within the geologic timescale.

The most important method is radiometric dating, which relies on the predictable decay of radioactive parent isotopes to stable daughter products. Common systems include uranium–lead (U–Pb) in zircon and other minerals, potassium–argon (K–Ar), rubidium–strontium (Rb–Sr), lutetium–hafnium (Lu–Hf), samarium–neodymium (Sm–Nd), and rhenium–osmium (Re–Os). Many methods can date from thousands to billions of years, but require minerals that have remained a closed system since formation. Isochron techniques help remove the need to know the original daughter amount.

In addition, radiocarbon dating (14C) is used for organic materials up to about 50,000 years, while luminescence dating (optically stimulated luminescence) constrains the last exposure to light for sediments. Other approaches include fission-track dating, cosmogenic nuclide dating, uranium-series dating, and electron spin resonance. These methods often complement each other and are cross-checked against stratigraphy and fossil records.

Geochronology contributes to building the geological timescale, correlating events across regions, and understanding processes such as plate tectonics, mountain building, volcanic activity, and paleoclimate change. Limitations include sample alteration, open-system behavior, diagenesis, and analytical uncertainties, necessitating careful method selection and multiple independent dates.