Harold Clayton Urey (April 29, 1893 – January 5, 1981) was an American physical chemist who conducted pioneering work on isotopes. He earned the 1934 Nobel Prize in Chemistry "for his discovery of heavy hydrogen." He played a significant role in the development of the atom bomb, as well as contributing to theories on the development of organic life from non-living matter.
Born in Walkerton, Indiana, Urey studied thermodynamics under Gilbert N. Lewis at the University of California, Berkeley. After he received his PhD in 1923, he was awarded a fellowship by the American-Scandinavian Foundation to study at the Niels Bohr Institute in Copenhagen.