Evolution of dating from 1940

It showed all of Libby’s results lying within a narrow statistical range of the known ages, thus proving the success of radiocarbon dating.Top of page The “Curve of Knowns” compared the known age of historical artifacts associated with the Bible, Pompeii, and Egyptian dynasties with their age as determined by radiocarbon dating.

Libby and graduate student Ernest Anderson (1920–2013) calculated the mixing of carbon across these different reservoirs, particularly in the oceans, which constitute the largest reservoir.

Their results predicted the distribution of carbon-14 across features of the carbon cycle and gave Libby encouragement that radiocarbon dating would be successful.

Willard Libby (1908–1980), a professor of chemistry at the University of Chicago, began the research that led him to radiocarbon dating in 1945.

He was inspired by physicist Serge Korff (1906–1989) of New York University, who in 1939 discovered that neutrons were produced during the bombardment of the atmosphere by cosmic rays.

To test the technique, Libby’s group applied the anti-coincidence counter to samples whose ages were already known.

Among the first objects tested were samples of redwood and fir trees, the age of which were known by counting their annual growth rings.Radiocarbon dating would be most successful if two important factors were true: that the concentration of carbon-14 in the atmosphere had been constant for thousands of years, and that carbon-14 moved readily through the atmosphere, biosphere, oceans and other reservoirs—in a process known as the carbon cycle.In the absence of any historical data concerning the intensity of cosmic radiation, Libby simply assumed that it had been constant.In a system where carbon-14 is readily exchanged throughout the cycle, the ratio of carbon-14 to other carbon isotopes should be the same in a living organism as in the atmosphere.However, the rates of movement of carbon throughout the cycle were not then known.Using this sample and an ordinary Geiger counter, Libby and Anderson established the existence of naturally occurring carbon-14, matching the concentration predicted by Korff. Fortunately, Libby’s group developed an alternative. They surrounded the sample chamber with a system of Geiger counters that were calibrated to detect and eliminate the background radiation that exists throughout the environment.

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