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Uranium-lead dating, often abbreviated as U-Pb dating, is a geochronological method used to determine the absolute age of rocks and minerals. This technique relies on the radioactive decay of uranium isotopes into lead isotopes. Specifically, it tracks the decay of uranium-238 (²³⁸U) to lead-206 (²⁰⁶Pb) and uranium-235 (²³⁵U) to lead-207 (²⁰⁷Pb). Both decay chains have well-established half-lives, allowing for precise age calculations.

The principle behind U-Pb dating is that when a mineral crystallizes, it incorporates uranium into its structure, but it ideally excludes lead. Over time, as the uranium decays, lead accumulates within the mineral. By measuring the ratio of parent uranium isotopes to daughter lead isotopes, scientists can calculate how much time has passed since the mineral formed. The presence of two independent decay chains (²³⁸U-²⁰⁶Pb and ²³⁵U-²⁰⁷Pb) provides a powerful internal consistency check, as both ratios should yield the same age for a geologically closed system.

U-Pb dating is particularly valuable for dating very old rocks, including those from the Archean eon and even meteorites, providing insights into the early history of the Earth and the solar system. Common minerals dated using this method include zircon (ZrSiO₄), monazite, and titanite. Zircon is highly favored due to its durability, resistance to alteration, and its tendency to exclude common lead during crystallization, making the measured lead primarily radiogenic. The accuracy and reliability of U-Pb dating have made it a cornerstone of geological dating.