3 radioactive elements in absolute dating
Consider some molten rock in which isotopes and elements are distributed in a reasonably homogeneous manner.Its composition would be represented as a single point on the isochron plot: Note that the above is somewhat simplified.
(The range of uncertainty varies, and may be as much as an order of magnitude different from the approximate value above.It is not easily explained, in the general case, in any other way.The data points would be expected to start out on a line if certain initial conditions were met.Unfortunately, one must wade through some hefty math in order to understand the procedures used to fit isochron lines to data.General comments on "dating assumptions" All radiometric dating methods require, in order to produce accurate ages, certain initial conditions and lack of contamination over time.However, the methods must be used with care -- and one should be cautious about investing much confidence in the resulting age...
especially in absence of cross-checks by different methods, or if presented without sufficient information to judge the context in which it was obtained.
Age "uncertainty" When a "simple" dating method is performed, the result is a single number.
There is no good way to tell how close the computed result is likely to be to the actual age.
The better the fit of the data to the line, the lower the uncertainty.
For further information on fitting of lines to data (also known as regression analysis), see: Note that the methods used by isotope geologists (as described by York) are much more complicated than those described by Gonick.
It depends on the accuracy of the measurements and the fit of the data to the line in each individual case.) For example, with Rb/Sr isochron dating, any age less than a few tens of millions of years is usually indistinguishable from zero.