Isochron dating methods

For a much more detailed discussion of isochrons and a variety of possible problems with them, and how geologists attempt to solve them, see

Contamination from outside, or the loss of isotopes at any time from the rock's original formation, would change the result.

It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.

The idea of isochrons is this: Suppose X is a parent element that decays in to Y and Z is another isotope of Y not produced by radioactive decay. Since Y and Z are isotopes, we would assume they have similar chemical properties.

Let's assume that initially, the ratio of y and z is constant, and then X begins decaying to Y.

Then if a mixture of Y and Z enters, a nice isochron yielding a false age will be produced.

A final possibility is for A to have a constant ratio of X and Y at the beginning. Then the rock is heated and mixed so the ratio of X and Y is everywhere the same. Finally, a mixture of Y and Z enters, different amounts at different places.

Different dating methods may be needed to confirm the age of a sample.

For example, a study of the Amitsoq gneisses from western Greenland used five different radiometric dating methods to examine twelve samples and got agreement to within 30 million years on an age of 3,640my.

A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will spontaneously change into a different nuclide by radioactive decay.

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