| Citation | Allegre is distinguished for his contributions to geochemistry and cosmochemistry, and especially for his ability to use accurate measurements of isotopic ratios to understand the evolution of the Earth's core, mantle, crust, oceans and atmosphere, and that of the solar system. Several of his contributions have been especially important. He was one of the first to exploit the decay of [147] Sm to [143] Nd to study continent formation by melt separation from the upper mantle. He realised how important the radioactive disequilibrium between [230] Th and its parent [238] U is, as a method of dating young limestones, as a probe of mantle processes, and as a method of studying melt production beneath ridges and island arcs. He pioneered the use of the [187] Re - [187] Os system, which is now extensively used to measure the age of the mantle part of the lithosphere beneath the continents. His work on Ar and Xe isotopes in ocean floor basalts clearly identified an [129] Xe excess in the mantle, and set new standards in rare gas measurements on terrestrial materials. He has also used a wide range of isotopic systems to study the origin and evolution of the Moon and of meteorites. Allegre has been actively involved in scientific administration in France, and conceived the idea of the European Union of Geosciences, which has become one of the most successful European scientific societies. Allegre is a Foreign Associate of the US National Academy of Sciences. In 1986 he was awarded the Crafoord Prize (jointly with G Wasserburg) for his pioneering work in isotope geology. |