Friday, February 24, 2006

Neanderthals Pushed Out Quickly

From Michael Hopkin at news:

Advances in the science of radiocarbon dating - a common, but oft-maligned palaeontological tool - have narrowed down the overlap between Europe's earliest modern humans and the Neanderthals that preceded them.

Previous estimates suggested that at least 7,000 years elapsed between H. sapiens arriving in eastern Europe more than 40,000 years ago, and the disappearance of the last known Neanderthals (H. neanderthalensis) from western France. But newly calculated dates shrink the overlap to 5,000 years.

Carbon dating is based on the rate of decay of radioactive carbon-14 atoms found in living matter such as bones. Because carbon-14 decays to a non-radioactive form over time, older samples give off less radiation.

But carbon-14's half-life is 5,730 years. So any sample older than about 30,000 years will have only 3% of its original carbon-14. For such samples, even tiny amounts of contamination can yield wildly inaccurate results.

Two key advances have put carbon dating back on the map. By 'ultrafiltering' bone samples to get rid of smaller molecules and retain only the larger ones, researchers can prepare far purer samples. And recent analysis of sea sediments from the Cariaco Basin near Venezuela have provided the most accurate record yet of how environmental carbon-14 levels have fluctuated, allowing the technique to be calibrated back to around 50,000 years.

All this means that modern humans' displacement of the Neanderthals was probably swifter than previously thought. Previous dating had suggested that H. sapiens arrived in Europe 43,000 years ago, and covered the continent by 36,000 years ago. But the refined figures are 46,000 and 41,000 years, says Mellars - just 5,000 years to colonize an entire continent.

He suspects that our bulky cousins, despite being well adapted to cold, were killed off by a "double whammy" of competition with humans and a climatic cold snap that occurred at around the same time. "I would be surprised if the two species coexisted in any one place for more than around 1,000 years," Mellars says.