Uranium-thorium-lead datingDifference between uranium and thorium dating called Common-lead Datingmethod of establishing the time of origin of a rock by means of the amount of common lead it contains; common lead is any lead from a rock or mineral that contains a large amount of lead and a small amount of the radioactive progenitors of lead—i. The important characteristic of common lead is that it contains no significant proportion of radiogenic lead accumulated since the time that mineral or rock phase was formed.
Of the four isotopes of lead, two are formed from the uranium isotopes Difference between uranium and thorium dating one is formed from the thorium isotope; only lead is not Difference between uranium and thorium dating 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 lead incorporated within the Earth has been evolving continuously from primordial lead and from the radioactive decay of uranium and thorium isotopes. 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. Difference between uranium and thorium dating modern lead, for example, from marine sediments or modern basalts has the composition of lead in the Earth and if the lead in the troilite phase of iron meteorites has the composition of primordial lead, then a simple model yields about 4.
This age is in good agreement with the age of the meteorites and the age of the Moon as determined independently. We welcome Difference between uranium and thorium dating improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
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The Editors Difference between uranium and thorium dating Encyclopaedia Britannica. Learn More in these related Britannica articles: The elements uranium and thorium gradually decay into lead, different isotopes of lead arising from the various isotopes of uranium and thorium; some isotopes of lead are, however, not produced by any radioactive decay process.
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