U and Th Decay Series Isotopes

For over half a century, uranium (U) and thorium (Th) decay series isotopes have been used as a chronometer and tracer of a range of geological and biological processes. In volcanic rocks, they can be used to help determine how magma is produced in a range of environments, how fast it is transported, and minerals that are precipitated in the process. They have also been used to date volcanic eruptions. In soils, U-series isotopes can estimate how fast parent material is weathered and converted into regolith. In fluvial sediments, they allow a determination of how long sediments have resided in a catchment. Uranium-series isotopes have also been applied to the study of groundwater, where they inform on the dissolution rate of the aquifer rock and the groundwater flow rate. In marine sediments, U- and Th-series isotopes have played a key role in improving our understanding of marine processes. For instance, they can quantify particular organic matter flux (with implications for the carbon cycle), and inform on particular transport and palaeo-productivity. Finally, U-series dating of carbonates such as corals has been instrumental in our understanding of past sea levels. The use of these isotopes in the dating of phosphates such as fossil bones and teeth has allowed us to directly date human fossils, with major implications for human evolution.