Harold C. Urey

American chemist

Urey discovered deuterium, the heavy isotope of hydrogen, as well as methods of isotope separation. He founded the modern science of cosmochemistry, devoted to understanding the origin and development of the solar system.

Born: April 29, 1893; Walkerton, Indiana

Died: January 5, 1981; La Jolla, California

Primary fields: Chemistry; physics; astronomy

Specialties:Physical chemistry; cosmochemistry

Early Life

Harold Clayton Urey lived a life and had a career that spanned a period of rapid change and development in the United States and the world. By his own account, he was seventeen years old when he first saw an automobile; less than sixty years later, he held in his hand a rock from the surface of the moon.

After finishing high school, he spent three years as a teacher in country schools before entering the University of Montana, where he majored in biology. He had to work to stay in college; this included periods of employment as a waiter, a construction worker, and a biology instructor. When the United States entered World War I, Urey found a job as an industrial chemist in Philadelphia. He later said that this was one of the experiences that nudged him back toward a university career. He returned first to the University of Montana as an instructor for two years. Then, in 1921, he was admitted to graduate school in chemistry at the University of California, Berkeley.

Urey completed his PhD work in 1923 and moved on to the Niels Bohr Institute in Copenhagen on a fellowship. Danish physicist Niels Bohr was already established as the central figure in atomic and nuclear physics. Urey met many other leaders in physics and chemistry while in Europe.

Life’s Work

Urey returned to the United States to take a teaching position at Johns Hopkins University. As a chemist with a strong grasp of physics, he had many lines of work open to him. His early papers were mainly related to the way molecules interact with light, using the then-new concepts of quantum theory to study a wide range of phenomena. In 1929, he moved to Columbia University.

Urey’s most important discovery came two years later. Chemists were searching the periodic table for stable isotopes, which are variants of any chemical element with the same number of protons as the element but different amounts of neutrons. Urey followed this subject closely, since he foresaw the potential significance of these isotopes to many fields. After the discovery of the heavy isotopes of oxygen, he saw what had not been seen by others, namely, that this implied the existence of a rare heavy isotope of the lightest element, hydrogen. This had been searched for earlier, as part of a general survey, but not with the intensity and skill Urey and his collaborators then brought to the task. In a matter of months, they succeeded.

This isotope is so distinct from light hydrogen that Urey gave it a special name, deuterium (meaning “the second one”). Water made with it (“heavy water”) boils at a temperature a few degrees higher than the usual kind and even looks slightly different. The chemical properties of hydrogen and deuterium are different enough that aquatic organisms cannot live in pure heavy water.

The award of the Nobel Prize to Urey in 1934 sealed his reputation as a leader in his field. In the remaining years before World War II, Urey centered his efforts on the practical separation of isotopes on a scale large enough to permit the power of isotopic methods to be exploited in physical and chemical research. He worked with deuterium and with heavy isotopes of carbon, nitrogen, oxygen, and chlorine, all essential elements for life. He also served as the first editor of the Journal of Chemical Physics, which became the most widely read journal in the field.

When atomic energy and atomic weapons became popular around 1940, Urey’s Columbia colleagues Enrico Fermi and Leo Szilard were among the first to undertake work in the field. Urey led the effort to separate the fissionable isotope of uranium, U-235, from the much larger mass of U-238 in the natural element. He also became the director of the Special Alloyed Materials (SAM) Laboratory at Columbia.

Urey always had a strong interest in politics, and the destruction of Hiroshima and Nagasaki gave him a feeling of personal responsibility that he never lost. Especially in the early postwar years, when he had moved to the University of Chicago together with Fermi, the Mayers, Szilard, Willard Libby, Edward Teller, and others, he spent much of his time writing, speaking, and lobbying in an effort to bring nuclear weapons and nuclear power under control in some internationally viable way.

Returning to the laboratory, he found that his prewar research interests had lost their excitement for him, and he looked for new directions. He found them in the natural world. His deep knowledge of isotopic processes was first applied to the Urey temperature scale, a method of determining the temperatures at which organisms grew (or rocks formed) in ancient periods, using the subtle isotopic patterns of oxygen found in fossil shells or rocks. With his students, he pioneered studies that made clear the history of ice ages and even of the life cycles of species long extinct.

Meanwhile, Urey broadened this historic interest to a general search for understanding of the earliest records of the origin of the Earth, sun, and planets, and of the origin of life. Immersing himself in the literature of the subject, he quickly came to believe that he could do better. His resulting book, The Planets: Their Origin and Development (1952), raised the discussion of the subject to a new level and contributed to the early development of cosmochemistry, the study of the chemical properties of the matter that makes up the universe. Two other landmark papers, one with his student Harmon Craig on meteorites and one with Hans Suess on the abundance of the elements, marked further progress. Urey’s student Stanley Miller performed a classic experiment that gave support to Urey’s ideas on the origins of life.

In 1958, Urey moved to the new campus of the University of California, San Diego. The rapid growth of this university’s standing in science owed much to his inspiration and efforts. At the age of eighty, he was still working and publishing regularly. He published his last scientific paper at age eighty-four, after a long career during which he received many honors and medals.

Married for almost sixty years to Frieda Daum Urey, he had four children and numerous grandchildren.

Impact

Thanks to Urey’s findings, stable isotopes such as deuterium have become important tools in many fields of scientific research. The discovery of deuterium has had a great impact on both science and life in general; a central use is in the hydrogen (fusion) bomb. Heavy water, on the other hand, has a central role in nuclear reactor proceedings. Heavy-water reactors are manufactured in many countries, and heavy water may become even more important as nuclear energy becomes more widely used throughout the world.

The use of deuterated solvents (solvents whose hydrogens have been replaced with deuterium) has helped organic and analytical chemistry significantly in the identification of unknown compounds. The operation of certain sophisticated pieces of scientific equipment, such as the nuclear magnetic resonance (NMR) spectrometer, is based on the existence of isotopes such as deuterium.

Medicine has used deuterium to study biochemical and physiological changes in the human body. Successful results with deuterium have led to the use of other isotopes, such as carbon 14, in biochemistry.

Finally, the possible existence of a relationship between isotope abundance and temperature has aided research into the nature of the Earth’s climate from thousands and millions of years ago, as well as research intended to determine the age and formation of the solar system.

Bibliography

Brian, Denis. The Voice of Genius: Conversations with Nobel Scientists and Other Luminaries. 1995. Cambridge: Perseus, 2001. Print. Contains interviews with prizewinning scientists, including Urey.

Cohn, Mildred. “Harold Urey: A Personal Remembrance Part I.” Chemical Heritage 23.4 (2005): 8–48. Print. Presents the author’s experience of working with Urey, describing Urey’s research, teaching, and legacy for the next generation of scientists at Columbia University.

Rigden, John S. Hydrogen: The Essential Element. Cambridge: Harvard UP, 2000. Print. Outlines scientific discoveries about the element of hydrogen. Includes a chapter about Urey.