Absolute dating method that uses the decay patterns of a series of radioactive isotopes of uranium, usually 238U or 235U. Dates are usually based on the measurement of one of the uranium isotopes and a relatively short‐lived daughter isotope expressed as isotopic ratios. When uranium is precipitated as a trace constituent in surface outcropping minerals it begins producing daughter isotopes. In applying the technique for dating, samples are ideally chosen from chemically closed systems in which the isotopic ratio used to calculate the sample age was initially zero. The great value of uranium dating is that it can be applied to materials far more ancient than could be covered by radiocarbon dating, in exceptional cases back to 1 million years ago. The kinds of material that can be dated are also slightly different, and include coral, mollusc shells, marl, bone, teeth, caliche and calcretes, peat, wood, and detrital sediment.