Sunday, January 2, 2011

Prehistoric Hand Axes Older Than Once Thought

Europe's Stone Age has taken an edgy turn. A new analysis finds that human ancestors living in what is now Spain fashioned double-edged stone cutting tools as early as 900,000 years ago, almost twice as long ago as previous estimates for this technological achievement in Europe.

If confirmed, the new dates support the idea that the manufacture and use of teardrop-shaped stone implements, known as hand axes, spread rapidly from Africa into Europe and Asia beginning roughly 1 million years ago, say geologist Gary Scott and paleontologist Luis Gibert, both of the Berkeley Geochronology Center in California.

Evidence of ancient reversals of Earth's magnetic field in soil at two archaeological sites indicates that hand axes date to 900,000 years ago in one location and to 760,000 years ago in the other, Scott and Gibert report in the Sept. 3 Nature. Until now, most researchers thought that hand axes unearthed at these sites were made between 500,000 and 200,000 years ago.

Other European hand ax sites date to no more than 500,000 years ago. In contrast, hand axes date to roughly 1.7 million years ago in eastern Africa. And age estimates of 1.2 million years and 800,000 years for hand axes from two Israeli sites indicate that this tool-making style spread out of Africa long before the origin of Homo sapiens around 200,000 years ago. Archaeology Excavations in southern China have also yielded 800,000-year-old hand axes (SN: 3/4/00, p. 148). Fossils from ancient human ancestors have not been found with the Israeli and Chinese artifacts.

Earlier analyses of magnetic reversals in soil at other sites in southern Spain indicate that single-edged stone tools appeared there around 1.3 million years ago, Gibert says (SN: 1/4/97, p. 12). Population movements back and forth between Africa and Europe must have occurred at that time, possibly via vessels across the Strait of Gibraltar, he hypothesizes.

"Then at 900,000 years ago, we now have the oldest evidence of hand axes in Europe, which represents a second migration from Africa that brought a new stone-tool culture," Gibert says.

Scott and Gibert's "surprisingly old ages" for the Spanish hand axes bring the chronology of ancient Europe's settlement in line with that of Asia, remarks archaeologist Wil Roebroeks of Leiden University in the Netherlands. Europe contains relatively few stone-tool sites from around 1 million years ago, making it difficult to reconstruct the timing of ancient population pulses into the continent, Roebroeks says.

Although new estimated ages for soil layers at the Spanish sites appear credible, the suggestion that hand axes there are by far the oldest in Europe "is extremely daring, to put it mildly," comments archaeologist Robin Dennell of the University of Sheffield in England. In his view, the precise depth of the hand axes when they were unearthed several decades ago remains unclear. It's possible that these finds actually came from soil layers that Scott and Gibert place at no more than 600,000 years old, Dennell says.

Scott and Gibert first identified the geological position of specific magnetic reversals in sediment at an ancient lakeshore near the Spanish sites. Dates for these reversals have already been established in previous studies. The researchers compared these magnetic shifts to those at the hand ax sites to date the tools.

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