How to solve carbon 14 dating problem

This is a digitized version of an article from The Times’s print archive, before the start of online publication in 1996.To preserve these articles as they originally appeared, The Times does not alter, edit or update them.In principle, any material of plant or animal origin, including textiles, wood, bones and leather, can be dated by its content of carbon 14, a radioactive form of carbon in the environment that is incorporated by all living things.

They arrived at this conclusion by comparing age estimates obtained using two different methods - analysis of radioactive carbon in a sample and determination of the ratio of uranium to thorium in the sample.

In some cases, the latter ratio appears to be a much more accurate gauge of age than the customary method of carbon dating, the scientists said.

Dating Subject to Error But scientists have long recognized that carbon dating is subject to error because of a variety of factors, including contamination by outside sources of carbon.

Therefore they have sought ways to calibrate and correct the carbon dating method.

'' But at earlier times, the carbon dates were substantially younger than the dates we estimated by uranium-thorium analysis,'' he said.

'' The largest deviation, 3,500 years, was obtained for samples that are about 20,000 years old.'' One reason the group believes the uranium-thorium estimates to be more accurate than carbon dating is that they produce better matches between known changes in the Earth's orbit and changes in global glaciation. Fairbanks, a member of the Lamont-Doherty group, said that if the dates of glaciation were determined using the uranium-thorium method, the delay - and the puzzle - disappeared.

But the tree ring record goes no further, so scientists have sought other indicators of age against which carbon dates can be compared.

One such indicator is the uranium-thorium dating method used by the Lamont-Doherty group.

The best gauge they have found is dendrochronology: the measurement of age by tree rings.

Accurate tree ring records of age are available for a period extending 9,000 years into the past.

Carbon dating is used to work out the age of organic material — in effect, any living thing.

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