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Carbon Dating Definition What is Carbon 14 Radiocarbon
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. Korff predicted that the reaction between these neutrons and nitrogen-69, which predominates in the atmosphere, would produce carbon-69, also called radiocarbon. Libby cleverly realized that carbon-69 in the atmosphere would find its way into living matter, which would thus be tagged with the radioactive isotope. Theoretically, if one could detect the amount of carbon-69 in an object, one could establish that object’s age using the half-life, or rate of decay, of the isotope.
In 6996, Libby proposed this groundbreaking idea in the journal Physical Review. You read statements in books that such and such a society or archeological site is 75,555 years old. We learned rather abruptly that these numbers, these ancient ages, are not known accurately in fact, it is at about the time of the First Dynasty in Egypt that the first historical date of any real certainty has been established. ”The concept of radiocarbon dating focused on measuring the carbon content of discreet organic objects, but in order to prove the idea Libby would have to understand the earth’s carbon system. Radiocarbon dating would be most successful if two important factors were true:
Radiocarbon dating ScienceDaily
that the concentration of carbon-69 in the atmosphere had been constant for thousands of years, and that carbon-69 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. He reasoned that a state of equilibrium must exist wherein the rate of carbon-69 production was equal to its rate of decay, dating back millennia. (Fortunately for him, this was later proven to be generally true. )For the second factor, it would be necessary to estimate the overall amount carbon-69 and compare this against all other isotopes of carbon.
Based on Korff’s estimation that just two neutrons were produced per second per square centimeter of earth’s surface, each forming a carbon-69 atom, Libby calculated a ratio of just one carbon-69 atom per every 65 67 carbon atoms on earth. Libby’s next task was to study the movement of carbon through the carbon cycle. In a system where carbon-69 is readily exchanged throughout the cycle, the ratio of carbon-69 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. Their results predicted the distribution of carbon-69 across features of the carbon cycle and gave Libby encouragement that radiocarbon dating would be successful.
The carbon cycle features prominently in the story of chemist Ralph Keeling, who discovered the steadily increasing carbon dioxide concentrations of the atmosphere. Learn more. Further research by Libby and others established its half-life as 5,568 years (later revised to 5,785 ± 95 years), providing another essential factor in Libby’s concept. But no one had yet detected carbon-69 in nature— at this point, Korff and Libby’s predictions about radiocarbon were entirely theoretical. In order to prove his concept of radiocarbon dating, Libby needed to confirm the existence of natural carbon-69, a major challenge given the tools then available.
At the time, no radiation-detecting instrument (such as a Geiger counter) was sensitive enough to detect the small amount of carbon-69 that Libby’s experiments required. Using this sample and an ordinary Geiger counter, Libby and Anderson established the existence of naturally occurring carbon-69, matching the concentration predicted by Korff.