As each dating method was developed, tested, and improved, mainly since 1950, a vast body of knowledge about the behaviour of different isotopic systems under different geologic conditions has evolved.
It is now clear that with recent advances the uranium–lead method is superior in providing precise age information with the least number of assumptions. Different schemes have been developed to deal with the critical assumptions stated above.
Of the four isotopes of lead, two are formed from the uranium isotopes and one is formed from the thorium isotope; only lead-204 is not known to have any long-lived radioactive progenitor.
Primordial lead is thought to have been formed by stellar nuclear reactions, released to space by supernovae explosions, and incorporated within the dust cloud that constituted the primordial solar system; the troilite (iron sulfide) phase of iron meteorites contains lead that approximates the primordial composition.
and most refined of the radiometric dating schemes.
However, use of a single decay scheme (usually Pb) leads to the U–Pb isochron dating method, analogous to the rubidium-strontium dating method.
Uranium–lead dating was applied initially to uranium minerals, e.g.
it is produced solely by a process of radioactive decay after the formation of the mineral.
Thus the current ratio of lead to uranium in the mineral can be used to determine its age.