Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.
Climate records from a Japanese lake are set to improve the accuracy of the dating technique, which could help to shed light on archaeological mysteries such as why Neanderthals became extinct.
Carbon dating is used to work out the age of organic material — in effect, any living thing.
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.
This method is based on the assumption (which nearly always holds true) that deeper layers of rock were deposited earlier in Earth's history, and thus are older than more shallow layers.
The successive layers of rock represent successive intervals of time.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.The clock was initially calibrated by dating objects of known age such as Egyptian mummies and bread from Pompeii; work that won Willard Libby the 1960 Nobel Prize in Chemistry.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.“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.