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.Students should be able to understand the principles and have that as a background so that age determinations by paleontologists and geologists don't seem like black magic. Geologists in the late 18th and early 19th century studied rock layers and the fossils in them to determine relative age.
Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology.
It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar).
The slope of the line determines the date, and the closeness of fit is a measure of the statistical reliability of the resulting date.
Technical details on how these dates are calculated are given in Radiometric dating. As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.
(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.
Ar (argon), the atom typically remains trapped within the lattice because it is larger than the spaces between the other atoms in a mineral crystal.
But it can escape into the surrounding region when the right conditions are met, such as change in pressure and/or temperature.
Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites.
In these materials, the decay product Ar is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies (recrystallizes).
The amount of Argon sublimation that occurs is a function of the purity of the sample, the composition of the mother material, and a number of other factors.