Harold Clayton Urey (1893–1981) was an American physical chemist whose work reshaped modern science. Born in Walkerton, Indiana, he grew up in a rural environment and initially trained as a teacher before pursuing higher education. After earning a bachelor’s degree in zoology from the University of Montana in 1917, he worked as a research chemist and later returned to academia, completing a PhD in chemistry at the University of California, Berkeley, in 1923.

Urey’s early career included a formative year at Niels Bohr’s Institute for Theoretical Physics in Copenhagen, which helped shape his scientific outlook. He went on to hold academic positions at several major institutions, including Johns Hopkins University, Columbia University, and the University of Chicago. His ground-breaking discovery of deuterium, an isotope of hydrogen, earned him the Nobel Prize in Chemistry in 1934 and established him as a leading figure in isotope research.

During World War II, Urey played a significant role in the Manhattan Project, overseeing a large team working on isotope separation. After the war, his interests expanded into planetary science and cosmochemistry. He proposed influential ideas about Earth’s early atmosphere and mentored Stanley Miller, whose Miller–Urey experiment demonstrated how organic molecules could form under primordial conditions. These contributions helped lay the foundation for modern studies of the origins of life.

Over his long career, Urey received numerous awards, including the National Medal of Science and the Gold Medal of the Royal Astronomical Society. He continued to influence scientific thought well into his later years, ultimately passing away in San Diego, California, in 1981. His legacy spans chemistry, planetary science, and our understanding of Earth’s early environment.