Bronk Ramsey’s team aimed to fill this gap by using sediment from bed of Lake Suigetsu, west of Tokyo.
Archaeologists vehemently disagree over the effects changing climate and competition from recently arriving humans had on the Neanderthals' demise.
The problem, says Bronk Ramsey, is that tree rings provide a direct record that only goes as far back as about 14,000 years.
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.
tree-ring dating) to calibrate their timescale (that is, to adjust it to compensate for the C-12 to C-14 ratio fluctuations).
By carbon dating a piece of wood which has also been dated by counting its annual tree-rings, scientists can create a table by which they can convert the questionable Carbon-14 years into true calendar years.