Mud at the bottom of Lake Suigetsu, Japan, could provide the most accurate way yet of calibrating radiocarbon dates.
     Every year for at least the last 60,000 years, a layer of algae has formed on the lake bed, in the mountains south of Nagano. Each layer includes the organic remains of leaves and twigs, which Christopher Bronk Ramsey at the University of Oxford and his colleagues have analysed to work out their carbon-14 content - a project that began more than a decade ago.
     Because counting the layers provides an independent way to establish exactly how old the organic remains are, the team used the information to work out exactly how much carbon-14 was in the atmosphere when the organic remains in each layer were trapped.
     "This is massively important," says Chris Turney, a climate scientist at the University of New South Wales in Sydney, Australia, who was not involved in the research. "You've got all these different records all scattered around the planet and nobody's known how to link them all in," says Turney.
     We already have an independent carbon-14 record that came from analysing tree rings, but it stretches back only 12,655 years.
     Radiocarbon dating expert Paula Reimer, an archaeologist from Queen's University Belfast, UK, says the accuracy with which we can determine an artefact's age could be improved by up to 1000 years as a result of this work.
     One of the joint leaders of the research, Takeshi Nakagawa at Newcastle University, UK, says the Lake Suigetsu data could help date artefacts that are 25,000 years old to within a century.

Edited from New Scientist (18 October 2012)