U-Th dating provides reliable ages beyond the ¹⁴C  range. It is an absolute dating technique which uses the differences radioactive half-life of the ²³⁸U (4.468 billion years) and ²³⁰Th (75,380 yrs). When the amounts of uranium and thorium are compared an accurate estimation of the age of an object up to about 500ka can be obtained. In fact the recent calibrations of the 14C curve depend upon U/Th dating.

The main assumption of this method is that uranium and thorium have not been migrated into or out of the material being tested. For example, bone and molluscs and foraminifera are open systems which can suffer from both leaching and uptake of Uranium from the environment.  U-Th analysis of this type of material can therefore result in erroneous ages.

Corals on the other hand make excellent candidates for this dating method as they are a closed system; the presence of thorium in the coral will be the result of uranium decay, not because the thorium has been taken up from sea water. Each analysis requires 30 to 50 mg of clean coral. If possible, samples with the highest amount of aragonite should be selected.!