U pb isotope dating dns updating software

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Planetary scientists maintain that they should, for reasons which are somewhat beyond the scope of this textbook.

As a result, we expect speleothems when they are first formed to contain some uranium but little or no lead — just like zircons.Uranium can and often does substitute for the element yttrium, whereas lead cannot, making xenotime suitable for radiometric dating.The key fact about xenotime is that since it has the same crystal structure as zircon, it can grow on zircon crystals, forming a crust; and this process, of course, cannot begin to take place while the zircon crystal is still locked inside its parent rock.It can be shown mathematically that if the rock has been undisturbed, so that the isotope ratios reflect nothing but the passage of time, then just as with the isochron diagrams we've already discussed (though for a different reason) the minerals so plotted will lie on a straight line on the graph; and the age of the rock can be calculated from the slope of the line.Unlike the ordinary isochron methods such as Rb-Sr, the Pb-Pb method does not allow us to deduce the original proportions of the various lead isotopes from the data acquired from the sample. We can do this by finding minerals that contain lead but never contained any uranium, or only ever contained it in negligible quantities.

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