In thin layers of carbonate deposits and in damp media, the uranium incorporated into the calcite during its crystallization may be partially eliminated because of its solubility in water.
Uranium leaching causes an artificial increase of the age thatmay reach considerable proportions (e.g.
Over the past several decades U–Th dating, also known as U-series disequilibrium dating, has been applied to geologic archives of past sea-level position such as fossil coral reefs, submerged speleothems, aragonite carbonate bank sediments, and fossil mollusks in beach deposits.
The isotopes protactinium-231 and thorium-230 are both radioactive and decay with half-lives of 32,500 years and 80,000 years, respectively.
The ratio of the two radioactive isotopes constitutes a better radioactive geochronometer than either of them separately, because they do not need to have a uniform sedimentation rate through time but need only be precipitated in the same proportion.
Consequently the ages obtained are minimum ages (terminus ante quem) which are frequently much younger than the real ages of the underlying artworks.
Moreover, a much more serious but rarely considered source of error contradicts the assumption of a closed system.
Most scientists today believe that life has existed on the earth for billions of years.
This belief in long ages for the earth and the existence of life is derived largely from radiometric dating.To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating.Radiometric dating is largely done on rock that has formed from solidified lava.Dramatic progress was seen in 14C-dating with the introduction of accelerator mass spectroscopy (AMS) which made possible the direct dating of prehistoric artworks painted or drawn with charcoal.However, in the case of engravings and red paintings, only indirect methods can be used that allow us to date deposits that have covered the works over time (TL, U/Th, oxalates, etc.).The uranium/thorium dating method gives reliable and relatively precise results in the case of massive speleothems, because the sampling is carried out at the heart of the material where the hypothesis of a closed system (that is, no exchange with the outside environment) is justified in most cases.