Good question Barry. Nobody really knows what happens in the earth's core.
Here is a comment at K-Ar dating:
Potassium argon dating assumes that there is “no radiogenic argon present when the rock is formed.” The theory states that since argon “is a gas” is cannot be retained by the crystallising minerals. However, igneous rocks cool slowly and it is known that olivine, in particular, can absorb argon in solution. So, the great assumption in K-Ar method is flawed.
Further, radiogenic argon that is created via the K-Ar decay can escape the rock. K-Ar dating of metamorphic rocks often show unusual results as the heating and re-crystallising allows argon to escape.
Further, igneous intrusions are not just a one time crystallizing event. An igneous mass can be formed, partially solidify and then melt again or just partially melt and so on and so forth. This process can go on through these melt/reform cycles for millions of years. The idea that there was no radiogenic argon present at the formation of the rock is a gross simplification.
Years ago, I took a course in geophysics and a well respected expert in what was called radiometric dating was asked why there was any question about the differences in dating the rocks of the geologic record if this method was accurate. He replied that the method was indeed accurate but one had to use the dating method in context with other information about the particular rock formation in question. He implied that using radiometric data alone would mislead one in determining the age of rock. I assume he answered that way due in part to his knowledge of the aformentioned difficulties.
TF
