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Currently, the concentration of carbon-14 in the atmosphere has been diluted, increasing the radiocarbon age of our atmosphere by 30 years per year."We can see from atmospheric observations that radiocarbon levels are steadily decreasing," Graven says in a statement.First, the older the object, the less carbon-14 there is to measure.Radiocarbon dating is therefore limited to objects that are younger than 50,000 to 60,000 years or so.It cannot be applied to inorganic material such as stone tools or ceramic pottery.The technique is based on measuring the ratio of two isotopes of carbon.And according to findings published in Proceedings of the National Academy of Sciences this week, it might become impossible to tell new things from centuries-old things. Carbon-14 is a naturally occurring, radioactive form of carbon, and it decays over thousands of years.
Business-as-usual emissions, on the other hand, would deplete atmospheric radiocarbon by the equivalent of 2,000 years of radioactive decay by 2100.Conversely, contamination by newer plant matter carried by flowing water or intruding plant roots may result in a date that is much too young. The original technique was based on counting the number of individual radioactive decay events per unit of time, using a device similar to a Geiger counter.Archaeologists are acutely aware of these and other potential difficulties, and take extreme care in the selection and handling of objects to be dated. In the 1970s a new technique was developed called Accelerator-based Mass Spectrometry (AMS), which counts the number of carbon-14 atoms directly.There are eight AMS laboratories currently operating in the Unites States.In Arizona, virtually all dating is performed by the Arizona Accelerator Mass Spectrometry (AMS) Laboratory at the University of Arizona in Tucson.