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Uranium thorium radiometric dating

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Zircon is especially useful because it frequently contains uranium in substitution for zirconium, but does not incorporate lead (as shown by the absence of Lead-204).

Thus all the lead in the zircon can be assumed to be radiogenic.

Thus, the lead isotopic composition of any mineral or rock depends upon its age and the environment from which it was formed; that is, it would depend upon the ratio of uranium plus thorium to lead in the parent material.

The Earth can be assumed to be a very large sample containing lead evolving from primordial lead by radiogenic increments.

To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating.

The most common dating method involves the use of minerals like zircon and monazite that are relatively common in granitic rocks.

Uranium 235 decays to lead 207, and Thorium 232 decays to lead 208.

In addition there is another stable isotope, lead 204, that is entirely primordial and does not form via radioactive decay at all.

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 lead incorporated within the of uranium and thorium isotopes.

Thus any of the radioactive isotopes and its lead daughter product can be used for dating, or a combination may be used.

In addition, some of the longer-lived intermediate daughter products have uses in dating.

These elements are usually present in constant (equilibrium) amounts in a sample, as long as the system remains closed.

A closed system is one in which there is no free exchange of elements in a material with the outside environment.

This will give us the precise measure of time that has elapsed since the disruption.

The basic principle of uranium – thorium series dating in corals is that uranium in oxygenated environments is about ten thousand times more soluble in seawater than thorium is.