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The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below).
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-thorium dating has an upper age limit of somewhat over 500,000 years, defined by the half-life of thorium-230, the precision with which we can measure the thorium-230/uranium-234 ratio in a sample, and the accuracy to which we know the half-lives of thorium-230 and uranium-234.
Note that to calculate an age using this technique the ratio of uranium-234 to its parent isotope uranium-238 must also be measured.
Therefore, one can assume that the entire lead content of the zircon is radiogenic, i.e.
The half-lives of the cascade from uranium-235 to lead-207 has been been extrapolated to about 704 million years and the cascade form uranium-238 to lead-206 has been calculated to about 4.47 billion years.Uranium-Lead dating is a radiometric dating method that uses the decay chain of uranium and lead to find the age of a rock.As uranium decays radioactively, it becomes different chemical elements until it stops at lead.In contrast, uranium is soluble to some extent in all natural waters, so any material that precipitates or is grown from such waters also contains trace uranium, typically at levels of between a few parts per billion and few parts per million by weight.As time passes after the formation of such a material, uranium-234 in the sample, with a half-life of 245,000 years, decays to thorium-230.