removing exterior portions of minerals that may have suffered Pb-loss, which, combined with improved magnetic separation methods, greatly improved the accuracy and precision of zircon geochronology. In addition, Krogh's laboratory methods for the dissolution of minerals and the subsequent chemical separation of trace quantities of uranium and lead resulted in a significant reduction of environmental Pb contamination (blank) to ultra-low levels, and permitted increasingly small quantities of mineral grains and sub-grain domains to be analyzed. In the mid-1980s, he was instrumental in producing a synthetic 205Pb isotopic tracer (spike) that was distributed for use in U-Pb geochronology laboratories worldwide. The application of Krogh's novel and innovative techniques has revolutionized U-Pb geochronology and permitted the ages of rocks to be determined with unprecedented accuracy and precision. Most of what is known of the Earth's 4.5 billion-year history has been placed in precise geological sequence using these dating methods. Honors 1989, awarded the Logan Medal by the Geological Association of Canada 1990, made a fellow of the American Geophysical Union 1991, bestowed an honorary D.Sc. by Queen's University 1991, awarded the J. Tuzo Wilson Medal by the Canadian Geophysical Union 1994, became an elected member of the Norwegian Academy of Science and Letters 1995, became a distinguished fellow of the Geological Association of Canada 1996, awarded the Past President's Medal by the Mineralogical Association of Canada 1997, became a Geochemistry Fellow of the Geochemical Society and European Association of Geochemistry 1999, became an elected fellow of the Royal Society of Canada Select publications Davis, D.W., Williams, I.S., Krogh, T.E., 2003. Historical development of zircon geochronology. In Reviews in Mineralogy and Geochemistry, J.M. Hanchar and P.W.O. Hoskin (Editors) volume 53, p. 145-181. Krogh, T.E., Kamo, S.L., Gower, C. and Owen, J.V., 2002. Augmented and reassessed U-Pb geochronological data from the Labradorian-Grenvillian front in the Smokey archipelago, eastern Labrador. Canadian Journal of Earth Sciences 39: 831-843. Krogh, T.E., Kamo, S.L. and Bohor, B. 1996. Shock metamorphosed zircons with correlated U-Pb discordance and melt rocks with concordant protolith ages indicate an impact origin for the Sudbury Structure. In Earth Processes: reading the isotopic code. A. Basu and S. Hart, eds. Geophysical Monograph 95, Washington, D.C.: American Geophysical Union, pp. 343–353. Chen, Y. D., Krogh, T. E., Vetrin, V. R. and Mitrofanov, F. P. 1994. Precise zircon geochronology on Archean rocks sampled by the world's deepest continental borehole, SD-3 Superdeep Well, Kola Peninsula, Russia. ICOG-8 Program