This will be discussed in more detail in the section on Gill's paper below.

The "generic" method described by Gonick is easier to understand, but it does not handle such necessities as: (1) varying levels of uncertainty in the X- versus Y-measurements of the data; (2) computing an uncertainty in slope and Y-intercept from the data; and (3) testing whether the "fit" of the data to the line is good enough to imply that the isochron yields a valid age.

The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth.

The equation is the one which describes radioactive decay: If one of these assumptions has been violated, the simple computation above yields an incorrect age.

Whether there's a data point on the Y-axis or not, the Y-intercept of the line doesn't change as the slope of the isochron line does (as shown in Figure 5).

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.

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.

(Rocks which include several different minerals are excellent for this.) Each group of measurements is plotted as a data point on a graph.

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