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Y., reported today in the British journal Nature that some estimates of age based on carbon analyses were wrong by as much as 3,500 years.
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.
Because it is radioactive, carbon 14 steadily decays into other substances.
But when a plant or animal dies, it can no longer accumulate fresh carbon 14, and the supply in the organism at the time of death is gradually depleted.
Using a mass spectrometer, an instrument that accelerates streams of atoms and uses magnets to sort them out according to mass and electric charge, the group has learned to measure the ratio of uranium to thorium very precisely.
The Lamont-Doherty scientists conducted their analyses on samples of coral drilled from a reef off the island of Barbados.
Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.
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.
Since 1947, scientists have reckoned the ages of many old objects by measuring the amounts of radioactive carbon they contain.
When finding the age of an organic organism we need to consider the half-life of carbon 14 as well as the rate of decay, which is –0.693.
For example, say a fossil is found that has 35% carbon 14 compared to the living sample. We can use a formula for carbon 14 dating to find the answer.
Therefore they have sought ways to calibrate and correct the carbon dating method.