The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated.Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay.
K-Ar dating was used to calibrate the geomagnetic polarity time scale.
Thermoluminescence testing also dates items to the last time they were heated.
An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.
It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record.
Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.