Harold Clayton Urey (Walkerton (Indiana), 29 april 1893 – La Jolla (California), January 5, 1981) was an American chemist. In 1934 won Urey the Nobel Prize in chemistry for his discovery of the hydrogen isotope deuterium.
Urey was born in Walkerton, the son of the schoolmaster and Reverend Samuel Clayton Urey and Cora Rebecca Reinsehl.  his father died when Harold was six years old; his mother remarried later with another pastor. He had a sister, Martha, and a brother, Clarence, and two half sisters, Florence and Ina. After the Kendallville High School he obtained a teachers certificate to the Earlham College in 1911. For three years he worked as a teacher at three different schools in Indiana and Montana.
He then went to the University of Montana where he earned a Bachelor's degree in zoology in 1917. He then worked for two years as research scheikundige in the industry before returning to Montana as an instructor chemistry.
In 1921 he entered the University of California, Berkeley to work under Professor Gilbert Lewis and where he obtained his doctorate in chemistry in 1923. At Berkeley, Urey influenced by the work of physicist Raymond t. Bridge and decided to join Niels Bohr in Copenhagen to work on the atomic structure at the Institute of theoretical physics.
After returning to the United States from 1924 to 1928, he taught at the Johns Hopkins University as Associate in Chemistry and then at the Columbia University. After completion of his book with Arthur Ruark, "Atoms, Molecules, and Quanta" – one of the first English-language books on quantum mechanics and its application in Atomic and molecular systems – hit Urey strongly interested in nuclear chemistry. Urey In 1934 was appointed Professor of chemistry at Columbia.
Starting from the 1930s began together with two colleagues, Ferdinand Brickwedde Urey and George m. Murphy, to investigate isotopes in particular to look for isotopes of hydrogen.  he believed that if there is a heavy hydrogen isotope existed this could be separated from ordinary hydrogen by evaporation of liquid hydrogen. Since the density of heavy hydrogen is larger it would be lighter, the first to evaporate and ordinary hydrogen a mixture remained behind rich in heavy hydrogen. Starting with four liters of liquid hydrogen remained after evaporation a milliliter about that after the heavy hydrogen isotope contained spectral analysis indeed. In this way he discovered in the hydrogen isotope deuterium 1932 , for which he was awarded the Nobel Prize in 1934. 
In the Second World War was Urey Director of the Substitute Alloys Material Laboratory at Columbia, one of the three main divisions of the Manhattan project. His main contribution was the development of the gaseous diffusion method to separate uranium-235 from uranium-238. Later he became an opponent of the use of nuclear energy for military as well as peaceful applications. In 1945 he became Professor of chemistry at the Fermi Institute for Nuclear Studies of the University of Chicago and from 1952 to 1958 he was Ryerson Professor of Chemistry to those University.
After the war, Urey focuses on the chemistry of the first life and he developed with one of his students in 1953, Stanley Miller, the famous Miller-Urey experiment (also known as the primordial soup experiment) with which he wanted to show that under the assumed conditions on the early Earth many building materials of life can arise spontaneously.
After a visiting professorship at Oxford (1956/57) spent the last years by Urey in California where he was Professor of chemistry at the University of California, San Diego (1958-70, emeritus 1970-81). He died in La Jolla, and was buried in the Fairfield cemetery in Dekalb Country, Indiana. He was married to Frieda Daum (1898-1992); they had three daughters and a son. 
In addition to the Nobel Prize, he was awarded the Willard Gibbs Medal (1934), the Davy medal (1940) of the Royal Society of London, the Franklin Medal (1943), the j. Lawrence Sahin Medal (1962), the Gold Medal of the Royal Astronomical Society (1966) and the Priestley Medal of the American Chemical Society in 1973. In 1964, he received the National Medal of Science.