Geochronologie

Geochronologie, or geochronology in English, is the science of determining absolute ages for rocks, minerals, fossils, and geological events. It provides time constraints on Earth’s history, complementing relative dating methods. The resulting ages underpin the geologic time scale and help interpret planetary evolution.

At the core is the concept of natural clocks. Radioactive isotopes decay at known rates, producing a measurable parent–daughter ratio that records the time since crystallization or formation. Reliable dating requires a closed system, accurate decay constants, and careful calibration.

Major methods include radiometric dating: uranium–lead dating (especially in zircon) for ancient rocks; potassium–argon and argon–argon dating for volcanic materials; and rubidium–strontium dating. Radiocarbon dating (carbon-14) is used for organic matter up to about 50,000 years. Other approaches are luminescence dating (OSL and TL), cosmogenic nuclide dating (Be-10, Al-26) for surface exposure ages, and fission‑track dating. Isochron methods and concordia plots help detect disturbed systems and provide cross-checks.

Results are integrated with stratigraphy and other dating methods to place events on the geological time scale. Uncertainties arise from measurement errors, uncertain decay constants, and potential changes in system conditions. Cross‑validation among methods and reference materials is standard practice to improve reliability.

Applications span tectonics, magmatic history, sedimentation rates, paleoenvironmental reconstruction, and biostratigraphy. Ongoing advances in instrumentation, sample preparation, and calibration continue to extend the reach and precision of geochronology, refining our understanding of Earth’s timeline and its climatic and biological history.