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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.The dating of meteorites would then help Patterson in determining not only the age of these meteorites but also the age of Earth’s formation.By dating meteorites Patterson was directly dating the age of various planetesimals.In uranium–lead (U–Pb) dating of zircon, the zircon is found to exclude initial lead almost completely.Minerals, too, are predictable chemical compounds that can be shown to form at......dating, for example, because most minerals do not take argon into their structures initially.

This is unstable and eventually decays to lead, which is stable.

Assuming the process of elemental differentiation is identical on Earth as it is on other planets, the core of these planetesimals would be depleted of uranium and thorium, while the crust and mantle would contain higher U/Pb ratios.

As planetesimals collided, various fragments were scattered and produced meteorites.

The method relies on two separate decay chains, the uranium series from Pb) leads to multiple dating techniques within the overall U–Pb system.

The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below).