Now that the mechanics of plotting an isochron have been described, we will discuss the potential problems of the "simple" dating method with respect to isochron methods.

The amount of initial wouldn't change over time -- because it would have no parent atoms to produce daughter atoms.

It is not easily explained, in the general case, in any other way.

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.

There are minor differences between isotopes of the same element, and in relatively rare circumstances it is possible to obtain some amount of differentiation between them. The effect is almost always a very small departure from homogeneous distribution of the isotopes -- perhaps enough to introduce an error of 0.002 half-lives in a non-isochron age. but it is rare and the effect is not large enough to account for extremely old ages on supposedly young formations.) as minerals form.

This results in a range of X-values for the data points representing individual minerals.

Isochron methods avoid the problems which can potentially result from both of the above assumptions.

Isochron dating requires a fourth measurement to be taken, which is the amount of a different isotope of the same element as the daughter product of radioactive decay.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.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.Consider some molten rock in which isotopes and elements are distributed in a reasonably homogeneous manner.