Therefore, the Y-intercept of the isochron line gives the initial global ratio of could be subtracted out of each sample, and it would then be possible to derive a simple age (by the equation introduced in the first section of this document) for each sample.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.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.(Rocks which include several different minerals are excellent for this.) Each group of measurements is plotted as a data point on a graph.The X-axis of the graph is the ratio of in a closed system 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.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.That encompasses the entire young-Earth timescale thousands of times over." in the decay equation.