⁴0</sup>Ar-³9</sup>Ar analysis may be used to test whether or not suspected hearths and cooking pits from archaeological sites of ancient people ever contained fires. Under some circumstances it may even be possible to deduce the intensity of use and to estimate ages for sites too old to be dated by conventional ¹4</sup>C analysis. This is done by using stepwise heating to measure argon loss from rocks caused by heating. It appears to be possible to determine if stones containing microcline or other potassium-bearing minerals were ever heated above ~ 500°C for 30 minutes or more.