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This method should also be applied only to minerals that remained in a closed system with no loss or gain of the parent or daughter isotope.
Uranium-Lead Dating Uranium-Lead (U-Pb) dating is the most reliable method for dating Quaternary sedimentary carbonate and silica, and fossils particulary outside the range of radiocarbon.
In contrast to a method such as Radiocarbon dating, which measures the disappearance of a substance, K-Ar dating measures the accumulation of Argon in a substance from the decomposition of potassium.
Argon, being an inert gas, usually does not leech out of a mineral and is easy to measure in small samples.
U-Pb ages of metamorphic minerals, such as zircon or monazite are used to date thermal events, including terrestrial meteoritic impacts.
U-Pb ages of zircon in sediments are used to determine the provenance of the sediments. Fission-track analysis is useful in determining the thermal history of a sample or region.
Potassium is a component in many common minerals and can be used to determine the ages of igneous and metamorphic rocks.By determining the number of tracks present on a polished surface of a grain and the amount of uranium present in the grain, it is possible to calculate how long it took to produce the number of tracks preserved.As long as the mineral has remained cool, near the earth surface, the tracks will accumulate.By measuring the C concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the number of decay events per gram of Carbon.By comparing this with modern levels of activity (1890 wood corrected for decay to 1950 AD) and using the measured half-life it becomes possible to calculate a date for the death of the sample. As a result of atomic bomb usage, C ages of objects younger than 1950.