Pb has been used for more than two decades to provide the geochronology of annually deposited sediments and to construct pollution histories.Evidence from some lakes suggests that this radionuclide may be adequately mobile to compromise dating reliability.
The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
Lava flows that lie above and below rock beds with ancient human fossils are a good—and true—example.
The mineral sanidine, the high-temperature form of potassium feldspar, is the most desirable.
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.
Any alteration or fracturing means that the potassium or the argon or both have been disturbed.