Urey, Harold C. (Clayton) (1893-1981), a United States physical chemist. In 1932 he discovered and isolated heavy hydrogen, or deuterium, and for this achievement, he was awarded the Nobel Prize in chemistry in 1934. Before World War II he devised methods of separating heavy water from ordinary water and for separating uranium 235 from uranium 238. Uranium 235 and heavy water were used in making the atomic bomb.

After World War II, Urey made studies concerning the origin of the solar system and of life on earth. He postulated that the planets originated by a process called accretion, in which small satellites of the sun collided and joined together. This theory was partly confirmed by evidence obtained from manned moon expeditions. His studies on the origin of life helped make possible the synthesizing of amino acids, the first step towards creating life by artificial means.

Urey was born in Walkerton, Indiana. He graduated from the University of Montana in 1917, and was awarded a Ph.D. at the University of California in 1923. He taught at Johns Hopkins University (1924-29) and Columbia University (1929-35). Urey was director of research for the atomic bomb project at Columbia in World War II. He was professor of chemistry at the University of Chicago, 1945-58, and professor-of-chemistry-at-large at the University of California, 1958-70.

Urey wrote Atoms, Molecules, and Quanta (with A. E. Ruark, 1930) and The Planets (1952).