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04/11/1995 07:00:00

Caltech Geologists Share 1995 Urey Medal

PASADENA—Sam Epstein and Hugh Taylor, both geologists at Caltech, and Robert Clayton of the University of Chicago jointly received the 1995 Urey Medal on April 10 at a ceremony in Strasbourg, France.

The Urey Medal is the highest award of the European Association of Geochemistry. The award, which consists of a medal and a certificate, is named for Harold C. Urey, the American chemist who discovered the isotope deuterium, a heavy form of the element hydrogen.

The award has special meaning for Epstein, because it was Harold Urey who first brought him to the University of Chicago as a postdoctoral fellow and got him started in the then new field of stable isotope geochemistry. All three cowinners have strong links to Caltech; Epstein and Taylor have both served on the faculty more than 35 years, and Clayton earned his PhD in chemistry and mathematics at Caltech in 1955. In fact, Clayton was Epstein's first PhD student, Taylor was his second, and both have published numerous articles jointly with Epstein.

The trio is well known for their pioneering work over four decades in the application of stable isotope geochemistry to the solution of problems ranging from the chemistry of the interstellar medium to the evolution of the moon and meteorites, the composition of the oceans through time, the variation in global temperature and climate over geological history, the circulation and heating of ground water in the earth's crust, the origin of igneous and metamorphic rocks and ore deposits, and the diets of prehistoric people.

Epstein, the William E. Leonhard Professor of Geology, Emeritus, earned his PhD in chemistry at McGill University in 1944. He is known for his studies of stable isotopes in materials as diverse as ice cores from the Greenland ice cap, moon rocks, and trees. An isotope is a form of an element in which the atoms are chemically identical, but each atom has a different number, usually one or two extra, of neutrons in its core.

By analyzing the relative ratios of different hydrogen and carbon isotopes in meteorites, Epstein verified that they contained preserved organic compounds which were not only extraterrestrial in origin, but were originally formed in interstellar space. And his analysis of isotopes in tree rings from around the world turned up evidence of a centuries-long global warming trend.

Taylor, the Robert P. Sharp Professor of Geology, earned both his BS and his PhD in geochemistry and geology at Caltech, in 1954 and 1959 respectively. Since then, he has been studying the oxygen and hydrogen isotope geochemistry of rocks throughout the world, as well as meteorites, lunar rocks, and ore deposits. Using isotopic analysis, he found that waters from the earth's surface (rain water and ocean water) circulate through fractures and openings in almost all rocks down to depths of five miles of more. Where these waters come close to bodies of molten rock, they become heated and convect upward, passing through overlying layers and altering these rocks' isotopic composition. Remarkably, he found that these isotopic changes can be detected even when the rocks melt to form magmas.

Taylor has shown that this is a very common phenomenon and an important process of heat transfer within the earth's crust. Furthermore, this circulating surface water is responsible for the formation of many valuable deposits of copper, gold, silver, and other metals. Prior to Taylor's studies, most scientists believed that such heated waters were derived directly from igneous rocks at great depths.

Contact: Jay Aller (818) 395-3631 aller@caltech.edu

Written by John Avery