Fluorine absorption dating
Encyclopedia
fluorine dating is used to determine the amount of time an object has been underground

Fluorine absorption dating can be carried out based on the fact that groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 contains fluoride ions. Items such as bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 fragments that are in the soil will absorb fluoride from the groundwater over time. From the amount of absorbed fluoride in the item, the time that the item has been in the soil can be estimated.

The dating method is a relative one because one needs another item found in the same area of which the age is known to state anything about a true age. If no real age is known, ages can only be expressed in older than or younger than between the two objects. The fluctuating amount of fluoride found in groundwater means the objects in comparison must be in the same local area in order for the comparisons to be accurate.

As not all objects absorb fluorine at the same rate, this also undermines the accuracy of such a dating technique. Although this can be compensated for by accommodating for the rate of absorption in calculations, such an accommodation tends to have a rather large margin of error
Margin of error
The margin of error is a statistic expressing the amount of random sampling error in a survey's results. The larger the margin of error, the less faith one should have that the poll's reported results are close to the "true" figures; that is, the figures for the whole population...

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