Radiometric dating age ranges
Instead of simply comparing the total potassium with the non-air argon in the rock, this method has a way of telling exactly what and how much argon is directly related to the potassium in the rock.
In the argon-argon method the rock is placed near the center of a nuclear reactor for a period of hours.
A nuclear reactor emits a very large number of neutrons, which are capable of changing a small amount of the potassium into argon Argon is not found in nature because it has only a year half-life.
This half-life doesn't affect the argon-argon dating method as long as the measurements are made within about five years of the neutron dose.
Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition.
However, construction of an isochron does not require information on the original compositions, using merely the present ratios of the parent and daughter isotopes to a standard isotope.This is called parentless argon because its parent potassium is not in the rock being dated, and is also not from the air.