The potassium-argon dating method has been used to measure a wide variety of ages.
The potassium-argon age of some meteorites is as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method.
The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.
Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.
The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).
Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.
However, because each of these parameters is difficult to determine independantly, a mineral standard, or monitor, of known age is irradiated with the samples of unknown age.
Laser probes also allow multiple ages to be determined on a single sample aliquot, but do so using accurate and precise spatial control.Step-heating is the most common way and involves either a furnace or a laser to uniformily heat the sample to evolve argon.The individual ages from each heating step are then graphically plotted on an age spectrum or an isochron.For example, laser spot sizes of 100 microns or less allow a user to extract multiple argon samples from across a small mica or feldspar grain.The results from a laser probe can be plotted in several graphical ways, including a map of a grain showing lateral argon distribution.