K has a half-life of 1.248 billion years, which makes it eminently suitable for dating rocks.Potassium is chemically incorporated into common minerals, notably hornblende, biotite and potassium feldspar, which are component minerals of igneous rocks.Although, organic materials as old as 100,000 years potentially can be dated with AMS, dates older than 60,000 years are still rare.
In other words, the change in numbers of atoms follows a geometric scale as illustrated by the graph below.other carbon isotopes in the same ratio as exists in the atmosphere.
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 severity of this problem decreases as the accuracy of our instruments increases.
Still, as a general rule, the proportional error in K-Ar dating will be greatest in the youngest rocks.