I'm a YEC. Challenge me.

[John V]

What?

If I have a rock that has K40 in it, and it cools forming a feldspar (KAl3Si3O8), it will then begin to spontaneously decay its K40 to Ar40.

If that rock remains undisturbed, then I could measure the ratio of K40 to Ar40 and use the rate of decay to get an age.

If however that rock is heated up and the crystal lattice expands due to a change in density, the Ar40 generated from the decay will escape as it does not fit into the structure of the feldspar crystal lattice. Resetting the age to 0. Then you close that system again and it starts over.

Meaning that you measure the heating event and not the original age.

NSS. And if this heating occurs early in the existence of the rock, then there won't be much of a difference from other methods.