Potassium 40 dating problems
The severity of this problem decreases as the accuracy of our instruments increases.
Any alteration or fracturing means that the potassium or the argon or both have been disturbed.
When a rock undergoes metamorphism, some or all of its argon can be outgassed.
If all the argon was lost, this would reset the K-Ar clock to zero, and dating the rock would give us the time of metamorphism; and if we recognized the rock as metamorphic this would actually be quite useful.
The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.
The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.
The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.