: Paléoclimatologie: U-Pb

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U-Pb

Uranium-lead dating is a radiometric dating method. Natural uranium consists mainly of two isotopes, uranium 235 and uranium 238. Uranium 235 decays with a half-life of around 700 million years; its stable final decay product is lead 207. Uranium 238 decays with a half-life of about 4.5 billion years; its final decay product is lead 206. In minerals that initially contained no lead, but whose crystalline lattice could incorporate uranium atoms (minerals such as zircon, monazite, titanite and a few others), measurement of the ratios 207Pb/235U and 206Pb/238U makes it possible to date the formation of the mineral, the two measurements leading to dates whose concordance ensures the reliability of the method. The reference curve is the concordia, plotted in a concordia-discordia diagram of increasing isotope ratios. This method can be used to date rocks that crystallised (at a closing temperature of 760 to 900°C for zircon) between around 1 million and over 4.5 billion years ago, with an accuracy of just 0.1 to 1%. (Adapted and translated from: https://fr.wikipedia.org/wiki/Datation_uranium-plomb)

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