Geologists measure the abundance of these radioisotopes instead to date rocks.
This is a digitized version of an article from The Times’s print archive, before the start of online publication in 1996.
Scientists at the Lamont-Doherty Geological Laboratory of Columbia University at Palisades, N.
Once the organism dies, it stops replenishing its carbon supply, and the total carbon-14 content in the organism slowly disappears.
Scientists can determine how long ago an organism died by measuring how much carbon-14 is left relative to the carbon-12.
Accurate tree ring records of age are available for a period extending 9,000 years into the past.
But the tree ring record goes no further, so scientists have sought other indicators of age against which carbon dates can be compared.