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Marine records, such as corals, have been used to push farther back in time, but these are less robust because levels of carbon-14 in the atmosphere and the ocean are not identical and tend shift with changes in ocean circulation.
Bronk Ramsey’s team aimed to fill this gap by using sediment from bed of Lake Suigetsu, west of Tokyo.
History, anthropology, and archaeology are three distinct but closely related bodies of knowledge that tell man of his present by virtue of his past.
Historians can tell what cultures thrived in different regions and when they disintegrated.
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 unstable and radioactive carbon 14, called radiocarbon, is a naturally occurring isotope of the element carbon.
The problem, says Bronk Ramsey, is that tree rings provide a direct record that only goes as far back as about 14,000 years.
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.
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.