Willard Frank Libby

Willard Frank Libby (born Dec. 17, 1908, Grand Valley, Colo., U.S.—died Sept. 8, 1980, Los Angeles, Calif.) was an American chemist whose technique of carbon-14 (or radiocarbon) dating provided an extremely valuable tool for archaeologists, anthropologists, and earth scientists. For this development he was honoured with the Nobel Prize for Chemistry in 1960.

Libby, the son of farmer Ora Edward Libby and his wife, Eva May (née Rivers), attended the University of California at Berkeley, where he received a bachelor’s degree (1931) and a doctorate (1933). After graduation, he joined the faculty at Berkeley, where he rose through the ranks from instructor (1933) to assistant professor (1938) to associate professor (1945). In 1940 he married Leonor Hickey, by whom he had twin daughters. In 1966 he was divorced and married Leona Woods Marshall, a staff member at the RAND Corporation of Santa Monica, Calif.

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In 1941 Libby received a Guggenheim fellowship to work at Princeton University in New Jersey, but his work was interrupted by the entry of the United States into World War II. He was sent on leave to the Columbia War Research Division of Columbia University in New York City, where he worked with Nobel chemistry laureate Harold C. Urey until 1945. Libby became professor of chemistry at the Institute for Nuclear Studies (now the Enrico Fermi Institute for Nuclear Studies) and the department of chemistry at the University of Chicago (1945–59). He was appointed by Pres. Dwight D. Eisenhower to the U.S. Atomic Energy Commission (1955–59). From 1959 Libby was a professor of chemistry at the University of California, Los Angeles, and director of its Institute of Geophysics and Planetary Physics (from 1962) until his death. He was the recipient of numerous honours, awards, and honourary degrees.

During the late 1950s, Libby and physicist Edward Teller, both committed to the Cold War and both prominent advocates of nuclear weapons testing, opposed Nobel chemistry and peace laureate Linus Pauling’s petition for a ban on nuclear weapons. To prove the survivability of nuclear war, Libby built a fallout shelter at his house, an event that was widely publicized. The shelter and house burned down several weeks later, however, which caused physicist and nuclear testing critic Leo Szilard to joke, “This proves not only that there is a God but that he has a sense of humor.”

While associated with the Manhattan Project (1941–45), Libby helped develop a method for separating uranium isotopes by gaseous diffusion, an essential step in the creation of the atomic bomb. In 1946 he showed that cosmic rays in the upper atmosphere produce traces of tritium, the heaviest isotope of hydrogen, which can be used as a tracer for atmospheric water. By measuring tritium concentrations, he developed a method for dating well water and wine, as well as for measuring circulation patterns of water and the mixing of ocean waters.

Because it had been known since 1939 that cosmic rays create showers of neutrons on striking atoms in the atmosphere, and because the atmosphere contains about 78 percent nitrogen, which absorbs neutrons to decay into the radioactive isotope carbon-14, Libby concluded that traces of carbon-14 should always exist in atmospheric carbon dioxide. Also, because carbon dioxide is continuously absorbed by plants and becomes part of their tissues, plants should contain traces of carbon-14. Since animals consume plants, animals should likewise contain traces of carbon-14. After a plant or other organism dies, no additional carbon-14 should be incorporated into its tissues, while that which is already present should decay at a constant rate. The half-life of carbon-14 was determined by its codiscoverer, chemist Martin D. Kamen, to be 5,730 years, which, compared with the age of the Earth, is a short time but one long enough for the production and decay of carbon-14 to reach equilibrium. In his Nobel presentation speech, Swedish chemist Arne Westgren summarized Libby’s method: “Because the activity of the carbon atoms decreases at a known rate, it should be possible, by measuring the remaining activity, to determine the time elapsed since death, if this occurred during the period between approximately 500 and 30,000 years ago.”

Libby verified the accuracy of his method by applying it to samples of fir and redwood trees whose ages had already been found by counting their annual rings and to artifacts, such as wood from the funerary boat of Pharaoh Sesostris III, whose ages were already known. By measuring the radioactivity of plant and animal material obtained globally from the North Pole to the South Pole, he showed that the carbon-14 produced by cosmic-ray bombardment varied little with latitude. On March 4, 1947, Libby and his students obtained the first age determination using the carbon-14 dating technique. He also dated linen wrappings from the Dead Sea Scrolls, bread from Pompeii buried in the eruption of Vesuvius (ad 79), charcoal from a Stonehenge campsite, and corncobs from a New Mexico cave, and he showed that the last North American ice age ended about 10,000 years ago, not 25,000 years ago as previously believed by geologists. The most publicized and controversial case of radiocarbon dating is probably that of the Shroud of Turin, which believers claim once covered the body of Jesus Christ but which Libby’s method applied by others shows to be from a period between 1260 and 1390. In nominating Libby for the Nobel Prize, one scientist stated, “Seldom has a single discovery in chemistry had such an impact on the thinking in so many fields of human endeavour. Seldom has a single discovery generated such wide public interest.”