Science: New Dating Game

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Archaeologists and paleontologists trying to ascertain the age of bone, wood and charcoal from ancient sites have long employed a technique called carbon-14 dating. This dating game has its drawbacks: it requires the destruction of a sizable portion of the sample and cannot, without costly and time-consuming treatment, determine the age of any object more than about 40,000 years old. But a new method promises to overcome both obstacles. A team of researchers from the University of Rochester, the University of Toronto and General lonex Corp. of Ipswich, Mass., is developing a way of dating objects that not only uses much smaller samples, but may also more than double the age that can be evaluated.

The method does not do away with the need to measure carbon 14, a radioactive atom that accumulates in all organisms while they live and decays at a known rate once they die. But it measures it in a different way. Current dating methods determine the age of an object indirectly, by measuring its carbon-14 radioactivity. The new technique being developed by Professor Harry Gove of Rochester and his fellow researchers measures the amount of carbon 14 directly. The scientists place a sample of the object to be evaluated in Rochester's tandem Van de Graaff particle accelerator. The machine separates carbon 14 and carbon 12, an atom that also accumulates at a steady rate but does not decay, from all other atoms in the sample. By comparing the ratio of these two types of carbon, the researchers can then calculate the age of the object under study.

Tiny Samples. Gove believes the direct measurement system, which requires as little as one-hundredth of the material needed for current dating tests, will eventually win wide acceptance. He and his colleagues have accurately determined some test samples to be 70,000 years old. With more work, they believe, they can push radiocarbon dating of tiny samples back to 100,000 years.