| Citation | Distinguished for the use of isotopes in the investigation of solar system history. He invented (with C.Merrihue) the 40Ar/39Ar method of radioactive dating and pioneered its application to terrestrial and extraterrestrial samples. By this method, Turner obtained the first precise K/Ar ages of the Apollo rocks, on which the remarkably complete chrononology of the early events in lunar history has been based, especially the early bombardment and basin formation and the evolution of the mare basalts. Also Thurner invented the 38Ar/37Ar method of cosmic ray dating which has provided ages of young impact craters which made the photogeological ages scale quantitative and has given values of surface erosion rates. Turner (with J.H.Reynolds) discovered the carbonaceous chondrite fission Xenon, one of four isotope anomalies which predate the formation of the solar system and he has demonstrated the near constancy of 129I: 127I in chondrites, important data concerning nuclear synthesis in stars. |