Metamorphic processes invalidate radiometric dating methods
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.
(For brevity's sake, hereafter I will refer to the parent isotope as ).
In addition, it requires that these measurements be taken from several different objects which all formed at the same time from a common pool of materials.
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.
Its composition would be represented as a single point on the isochron plot: Note that the above is somewhat simplified.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.Since the data points have the same Y-value and a range of X-values, they initially fall on a horizontal line: half-lives will include zero within its range of uncertainty.(The range of uncertainty varies, and may be as much as an order of magnitude different from the approximate value above.