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The sample age is based on the difference between the initial ratio of U with the environment (i.e., that it is a closed system.) The method is used for samples that can retain Uranium and Thorium, such as carbonate sediments, bones and teeth.
Ages between 1000 and 300,000 years have been reported.
Uranium/Thorium dating of ferricretes from mid- to late Pleistocene glacial sediments, western Tasmania, Australia.
Uranium-thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique commonly used to determine the age of calcium carbonate materials such as speleothem or coral.
Unlike other commonly used radiometric dating techniques such as rubidium-strontium or uranium-lead dating, the uranium-thorium technique does not measure accumulation of a stable end-member decay product.
Instead, the uranium-thorium technique calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium-230 and its radioactive parent uranium-234 within a sample.
Thorium is not soluble in natural waters under conditions found at or near the surface of the earth, so materials grown in or from these waters do not usually contain thorium.
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.