What is uranium series dating
Differential solubility between uranium and its long lived daughter isotope Th is measured using MC-ICPMS.
This method has a dating range up to about 600.000 years.
There are three such decay chains, each starts with an actinide nuclide (Th) having a long half live and ultimately ends with different a stable isotope of lead.
As traditional methods such as radiocarbon dating do not work where there is no organic pigment, the team dated the formation of tiny stalactites on top of the paintings using the radioactive decay of uranium. Where larger stalagmites had been painted, maximum ages were also obtained.
Thorium has a much shorter half-life of 75,000 years.
Unlike other types of radioactive dating, Uranium-Thorium (U-Th) dating doesn't reach a stable end point.
We use U-Th dating to obtain a chronology for stalagmites which are used for palaeoclimate research (pdf), dating carbonate crusts on cave art to derive minimum age constraints for underlying art(paper Hoffmann et al. (2012) (DOI: 10.1126/science.1219957),speleothem formations in stratigraphic relationship with archaeological artefacts, travertine formation in relation with archaeology.
Ages of older sites can be obtained with the K–Ar method, but only where volcanic deposits are interstratified with the archaeological deposits.
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Instead, the decay of Thorium and the production of Thorium reach a form of balance - called secular equilibrium.