| Citation | Professor Halliday is distinguished for the many and varied contributions he has made through the application of isotopic methods to problems in the Earth and Planetary Sciences. In his early career, these included applications to the timing and mechanism of ore deposits and granite formation. At the University of Michigan, a significant contribution involved the application 182Hf-182W chronometer to the timing of metal-silicate fractionation in meteorites, the Earth, Moon and Mars. These measurements based on the newly developed plasma-source mass spectrometry techniques impose severe constraints on the timing of the formation of the Earth's core and has stimulated wide interest in this subject |