1973: Harold C. Urey (1893–1981)

He once told colleagues that the first time he saw an automobile was at age 17 in rural Montana. But that didn’t stop him from becoming one of the greatest contributors to modern chemistry. His interests ranged from atomic structure to the chemistry of life.

Urey was born in the rural small town of Walkerton, Ind. After finishing high school in 1911, he taught for three years in country schools. He then entered the University of Montana, from which he received a B.S. in zoology in 1917. During the next four years, Urey worked as an industrial research chemist and as a chemistry instructor in his home state. And in 1923, under the tutelage of Gilbert N. Lewis, Urey earned a Ph.D. in physical chemistry from the University of California, Berkeley.

At UC Berkeley, Urey was influenced by the work of physicist Raymond T. Birge and soon joined Niels Bohr for one year in Copenhagen to work on atomic structure at the Institute for Theoretical Physics. After returning to the U.S., he taught at Johns Hopkins University and then at Columbia University, where he assembled a team of associates that included Rudolph Schoenheimer, David Rittenberg, and T. I. Taylor.

After coauthoring the book “Atoms, Quanta, and Molecules,” one of the first English texts on quantum mechanics and its applications to atomic and molecular systems, Urey became interested in nuclear systematics. This led to his discovery of deuterium.

On Thanksgiving Day in 1931, while at Columbia, Urey and his team experimentally proved the existence of deuterium by repeatedly distilling a sample of liquid hydrogen. He continued to make an impact on science throughout the 1930s by separating isotopes of oxygen, carbon, nitrogen, and sulfur, and by working on medical and biological applications of isotopes. He received the Nobel Prize in 1934.

Urey’s early research focused on the entropy of diatomic gases and problems of atomic and molecular structure and absorption spectra. Together with E. W. Washburn, he evolved the electrolytic method for the separation of hydrogen isotopes and investigated their properties—in particular the vapor pressure of hydrogen and deuterium and the equilibrium constants of exchange reactions.

During World War II, Urey’s team at Columbia worked on a number of research programs that contributed to the development of an atomic bomb for the U.S. Most important, they helped develop the gaseous diffusion method to separate uranium-235 from uranium-238. In the fall of 1941, Urey and others led a diplomatic mission to England to establish cooperation on development of the atomic bomb.

After the war, Urey first became professor of chemistry at the Institute for Nuclear Studies and then the Ryerson Professor of Chemistry at the University of Chicago before becoming University Professor, professor-at-large of chemistry, and professor emeritus at the University of California, San Diego. In retirement at UC San Diego, he published more than 100 research papers, many focused on understanding Earth’s moon.

After 1950, Urey’s interests turned to the chemistry of the planets, and he is credited with pioneering the rigorous study of “cosmochemistry,” a term that he coined. Urey led the effort to convince the National Aeronautic and Space Administration to initiate moon exploration.

He later worked on the separation of uranium isotopes, measurement of paleotemperatures (now universally used to analyze climate warming and cooling cycles), investigation into the origin of the planets, and study of the chemical problems of the Earth’s origin. His work on oxygen-18 led him to develop theories about the abundance of the chemical elements on Earth and of their abundance and evolution in the stars.

In his book “The Planets: Their Origin and Development,” Urey speculated that the early terrestrial atmosphere was probably composed of ammonia, methane, and hydrogen. In 1953, he and graduate student Stanley Miller performed a famous experiment on amino acid synthesis via electrical discharge in gases thought to be present in Earth’s original reducing atmosphere.—Alicia Chambers

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