Nature: Modern humans and Neanderthals probably coexisted for thousands of years, according to a new study published in Nature. Because that overlap occurred some 30 000–50 000 years ago, however, traditional radiocarbon dating techniques have proven unreliable for analyzing the organic remains. After 30 000 years, 98% of the carbon isotope has disappeared and younger carbon has started seeping in. Now Tom Higham of Oxford University and colleagues explain how they expelled the contaminating carbon and used accelerator mass spectrometry to measure the minuscule amounts of radiocarbon left in samples from 40 key archaeological sites across southern Europe. The technique has allowed them to verify that humans and Neanderthals lived contemporaneously for possibly as long as 5000 years. The long overlap would have provided plenty of time for cultural exchange and interbreeding, says Higham.
