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U-Th and 14C: historical aspects and useful similarities

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Edouard Bard

CEREGE, Collège de France, Université Aix-Marseille, CNRS, IRD

Europôle de l’Arbois, BP 80, F-13545 Aix-en-Provence, France, (


            These two widely used geochronological methods rely on fundamentally different processes and have their specific advantages and weaknesses. However, some of the analytical and geochemical issues for 14C bear many similarities to those experienced with U-Th dating. It is even interesting to make a brief historical perspective of both fields and consider how each scientific community has dealt with problems such as determining and updating the decay constants, insuring inter-lab standardization through the distribution of standards and the organization of measurement inter-comparisons, detecting altered samples and removing secondary contaminations.

            Each dating method also includes additional difficulties linked to second order deviations from the initial theory. Radiocarbon ages must be corrected for reservoir ages and calibrated by using a time variable correction based on a large compilation of 14C vs. true age comparisons based on various techniques. Accurate U-Th dating of marine carbonates implies the parallel study of 234U/238U ratios that has been shown to be variable through time in the ocean. The radiocarbon community has dealt with these challenges reaching some success. This may prove helpful in our struggle to accurately date corals with U-Th.

Last updated: September 9, 2009

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