Determining the age of fossils and other ancient objects could become more accurate, thanks to measurements of radioactive carbon-14 from a lake in Japan.
Radiocarbon dating is based on the steady decay rate of carbon-14 in samples, and archaeologists calibrate this carbon clock by comparing the known ages of tree rings with their carbon ages. But the tree-ring carbon record goes back only about 14,000 years, and less reliable marine records have been used to fill the gap. Christopher Ramsey at the University of Oxford, UK, and his colleagues extracted roughly 70-metre-long core samples from the bed of Lake Suigetsu. By counting the number of distinct sediment layers in the core — two layers have formed every summer and winter over the past 52,000 years — the team was able to compare the ages of the layers with their carbon-dated ages.
The more accurate carbon-14 record could help archaeologists to fine-tune the dates of key events, such as the coexistence of humans and Neanderthals.
Science 338, 370–374 (2012) http://dx.doi.org/10.1126/science.1226660
For a longer story on this research, see go.nature.com/pbv6ey