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| In the Laboratory Libby's discovery solved one of the key problems in archaeology, how to accurately date materials. Now that accurate dates could be given to individual artifacts, the relationship and development of artifacts found at different locations could be studied. Charcoal from wood provides some of the best samples for dating becauseit is almost pure carbon. Of course, there is always the risk that the woodwas already old when it was burnt and buried, so the carbon date might notbe totally reliable. Carbonized seeds, grains, beans, and peas canoften give more accurate dates because they are generally fresh when burntand buried. Bones can also be used, but a larger quantity is needed sincebone is not pure carbon. Once a sample has been collected, it is taken to a laboratory fortesting. In the lab, the sample is carefully cleaned to avoid contamination, then processed to extract the carbon. Unfortunately, this process destroys the sample because it must be smashed in order to isolate the carbon. After it has been smashed, the sample is loaded into a sophisticated radiation detector that measures the amount of carbon-14 in it. All carbon-14 dates are published with a "plus or minus" figure. Thisis because the level of radiation present in the atmosphere changes from dayto day, creating a small possibility of error in the results. Today, carbon dating is the most common type of test being done to determine the age ofarchaeological objects. A test costs from $250 to $800 and can be done atmore than seven hundred laboratories around the world.
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