Accuracy of carbon 14 dating
What this means is that there is an approximately constant fraction of the carbon in the world which is this radioactive carbon.
It gets taken from the air and used in photosynthesis by plants, and so all living things should have this same fraction of 14C in them as long as they are alive and actively exchanging matter with the environment.
Again, a lot of this depends on the sample and the method for measuring it.
I would like to add one key point: how do we know that the rate of carbon-14 production in the atmosphere has been constant?
Archaeologists vehemently disagree over the effects changing climate and competition from recently arriving humans had on the Neanderthals' demise.
The more accurate carbon clock should yield better dates for any overlap of humans and Neanderthals, as well as for determining how climate changes influenced the extinction of Neanderthals.
Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.
Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.
But even he “realized that there probably would be variation”, says Christopher Bronk Ramsey, a geochronologist at the University of Oxford, UK, who led the latest work, published today in Science.
As a rule, carbon dates are younger than calendar dates: a bone carbon-dated to 10,000 years is around 11,000 years old, and 20,000 carbon years roughly equates to 24,000 calendar years.
The problem, says Bronk Ramsey, is that tree rings provide a direct record that only goes as far back as about 14,000 years.
“If you’re trying to look at archaeological sites at the order of 30,000 or 40,000 years ago, the ages may shift by only a few hundred years but that may be significant in putting them before or after changes in climate,” he says.
Take the extinction of Neanderthals, which occurred in western Europe less than 30,000 years ago.