Uraniumlead dating

Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago. It relies on two separate decay chains, the uranium series from 238U to 206Pb, with a half-life of 4.47 billion years and the actinium series from 235U to 207Pb. The method is usually applied to zircon. This mineral incorporates uranium and thorium atoms into its crystal structure, but strongly rejects lead when forming. Since the exact rate at which uranium decays into lead is known, the current ratio of lead to uranium in a sample of the mineral can be use to reliably determine its age. Use of a single decay scheme leads to the U-Pb isochron dating method, analogous to the rubidium–strontium dating method. This is termed the lead– lead dating method and is most commonly used for minerals such as monazite, titanite, and baddeleyite.