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.

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Korff predicted that the reaction between these neutrons and nitrogen-14, which predominates in the atmosphere, would produce carbon-14, also called radiocarbon.

Libby cleverly realized that carbon-14 in the atmosphere would find its way into living matter, which would thus be tagged with the radioactive isotope.

Living organisms from today would have the same amount of carbon-14 as the atmosphere, whereas extremely ancient sources that were once alive, such as coal beds or petroleum, would have none left.

For organic objects of intermediate ages—between a few centuries and several millennia—an age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against the known half-life of carbon-14.

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.

Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms.

The “radiocarbon revolution” made possible by Libby’s discovery greatly benefitted the fields of archaeology and geology by allowing practitioners to develop more precise historical chronologies across geography and cultures.

Dedicated at the University of Chicago on October 10, 2016.

In 1946, Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon-14, a newly discovered radioactive isotope of carbon.

But no one had yet detected carbon-14 in nature— at this point, Korff and Libby’s predictions about radiocarbon were entirely theoretical.