US chemist best known for developing the technique of radiocarbon dating, for which he was awarded the 1960 Nobel Prize for Chemistry.
Libby was born in Grand Valley, Colorado, on 17 December 1908, the son of a farmer. He received his university education at the University of California, Berkeley, from which he graduated in 1931 and gained his PhD in 1933. He then took a teaching appointment at Berkeley and in 1941, soon after the outbreak of World War II, moved to Columbia University, New York, to work on the development of the atomic bomb (the Manhattan Project). After the war, in 1945, he became professor of chemistry at the University of Chicago's Institute for Nuclear Studies. From 1954 to 1959 he was a member of the US Atomic Energy Commission, then in 1959 he returned to the University of California to become director of the Institute of Geophysics. He died in Los Angeles on 8 September 1980.
During the early 1940s at Columbia Libby worked on the separation of uranium isotopes for producing fissionable uranium-238 for the atomic bomb. Back in Chicago after the war he turned his attention to carbon-14, a radioactive isotope of carbon that had been discovered in 1940 by Serge Korff. It occurs as a small constant percentage of the carbon in the carbon dioxide in the atmosphere - resulting from cosmic-ray bombardment - and in the carbon in the tissues of all living plants and animals. Carbon-14 has an extremely long half-life (5,730 years) but when the plant or animal dies, it accumulates no more of the radioactive isotope, which steadily decays and changes into nitrogen. Libby reasoned that a determination of the carbon-14 content of anything derived from plant or animal tissue - such as wood, bones, cotton or woollen cloth, hair, or leather - gives a measure of its age (or the time that has elapsed since the plant or animal died). He and his co-workers accurately dated ancient Egyptian relics by measuring the amount of radiocarbon they contained using a sensitive Geiger counter. By 1947 they had developed the technique so that it could date objects up to 50,000 years old. It has proved to be extremely useful in geology, anthropology, and archaeology. In 1946 Libby showed that tritium (a radioactive isotope of hydrogen of mass 3) is formed by the action of cosmic rays and devised a method of dating based on the amount of tritium in the water in an archaeological specimen. Later workers extended the method using other isotopes, such as potassium-40.