U pb dating

Zircon has a high hardness (7.5) which makes it resistant to mechanical weathering, and it is also very resistant to chemical weathering. Chemically, zircon usually contains high amounts of U and low amounts of Pb, so that large amounts of radiogenic Pb are produced.Other minerals that also show these properties, but are less commonly used in radiometric dating are Apatite and sphene.Furthermore, the half life of the parent isotope is much longer than any of the intermediary daughter isotopes, thus fulfilling the requirements for secular equilibrium (Section 2.4).We can therefore assume that the Some igneous minerals (notably zircon) conveniently incorporate lots of U and virtually no Pb upon crystallisation.Such losses cause the U-ratios which yield the same ages (t) against one another, they form a so-called ‘concordia’ curve.

This sometimes is not the case, resulting in a loss of Pb and/or U.For those minerals, the non-radiogenic Pb can be safely neglected (at least for relatively young ages), so that we can assume that .This assumption cannot be made for other minerals, young ages, and high precision geochronology.Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.

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