Carbon dating for
The Lamont-Doherty scientists conducted their analyses on samples of coral drilled from a reef off the island of Barbados.
The samples represented animals that lived at various times during the last 30,000 years. Alan Zindler, a professor of geology at Columbia University who is a member of the Lamont-Doherty research group, said age estimates using the carbon dating and uranium-thorium dating differed only slightly for the period from 9,000 years ago to the present.
Since 1947, scientists have reckoned the ages of many old objects by measuring the amounts of radioactive carbon they contain.
Some organic materials do give radiocarbon ages in excess of 50,000 "radiocarbon years." However, it is important to distinguish between "radiocarbon years" and calendar years.
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.
Carbon 14 is thought to be mainly a product of bombardment of the atmosphere by cosmic rays, so cosmic ray intensity would affect the amount of carbon 14 in the environment at any given time.
#30,000-Year Limit The Lamont-Doherty group says uranium-thorium dating not only is more precise than carbon dating in some cases, but also can be used to date much older objects.