Libby carbon dating earth radiometric dating
Carbon has different isotopes, which are usually not radioactive.Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and locality.Unlike most isotopic dating methods, the conventional carbon-14 dating technique is not based on counting daughter isotopes.It relies instead on the progressive decay or disappearance of the radioactive parent with time.Willard Libby of the United States began with his recognition that a process that had produced radiocarbon in the laboratory was also going on in Earth’s upper atmosphere—namely, the bombardment of nitrogen by free neutrons.
It is now clear that carbon-14 is not homogeneously distributed among today’s plants and animals.
The relatively short-lived C taken into organic matter is also slightly variable. However, under about 20,000 years the results can be compared with dendrochronology, based on tree rings.
For the most accurate work, variations are compensated by means of calibration curves.
He first demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from an ancient Egyptian royal barge of which the age was known from historical documents.
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