Fluorine absorption dating is a method used to determine the amount of time an object has been underground.
Fluorine absorption dating is based on the fact that groundwater contains fluoride ions.
Although this can be compensated for by including the estimated rate of absorption in calculations, such accommodations tend to have a rather large margin of error.
In 1953, this test was used by Kenneth Oakley to easily identify that the 'Piltdown Man' was forged, almost 50 years after it was originally 'unearthed'.
It was also used to disprove the validity of the Calaveras Skull, the first use of fluorine dating on human bone.