5 September 2009
Europe's oldest axes discovered
Archaeologists have long been puzzled by a 1-million-year pause between when early humans started making sophisticated hand axes with two-faced blades in Africa 1.5 million years ago and when the technology finally got to Europe. But new research is showing that advanced Stone Age tools got to Europe close to the time they reached other sites outside of Africa.
In a letter published in Nature, two archaeologists have shown that axes from southeastern Spain are from 900,000 years ago, much older than had been believed. That would mean it took about 600,000 years for the new ax-making technique to get to Europe. What was surprising was that older axes hadn't been found before in Europe, says archaeologist Luis Gibert, a co-author on the letter.
The work is credible, says Rick Potts, director of the Human Origins Program at the Smithsonian Institution's National Museum of Natural History in Washington, D.C. "If you asked me yesterday when were the earliest hand axes in Europe, I would say we have an excellent site in England called Boxgrove and that's about 500,000," he says. The new research has almost doubled that time period, from 500,000 to 900,000 years ago, Potts says.
Gibert and fellow author Gary Scott are at the Berkeley Geochronology Center, a research institute in Berkeley, Calif., that studies the history of the Earth and dating methods. They used analysis of changes in the Earth's magnetic fields to date the axes. Very fine-grained magnetic materials in the rock will orient themselves with the current magnetic field, making it possible to measure which era a given area came from by dating the polarity of the Earth's magnetic fields at the time. In addition to the palaeomagnetic technique, Gibert notes that a record in rock layers of the remains of micro-mammals such as rodents, developed by Walker's team at Estrecho del Quípar, was crucial in confirming the dates. The Solana del Zamborino cave hadn't been studied in more than 30 years.
Stone axes, called Acheulian by archaeologists, were "the Swiss Army Knife of the Stone Age," Potts says. 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. Homo neanderthalensis, Homo erectus and Homo heidelbergensis are all species known to be associated with Acheulian axes, which have two-sided cutting faces that were made of many types of stone for still-unconfirmed uses. They began to be replaced by a smaller, more mobile kit of specialized stone tools about 400,000 years ago, Potts says.
Perhaps even more interesting than the previous gap in the arrival of the hand-ax technology is why the axes weren't more popular outside Africa, says Ian Tattersall, curator in anthropology at the American Museum of Natural History in New York. Common at sites in Africa, the hand axes are much rarer in Europe and Asia. "That's the question: If this was such a revolutionarily wonderful new technology, why weren't they more widely used?" Tattersall says.
The older dates for the Spanish axes are now expected to generate new studies at other European rock shelters bearing Acheulian artefacts. But those studies may be hampered by the lack of appropriate sediments with which to identify palaeomagnetic polarity reversals, says Walker.
Sources: Nature (2 September 2009), Discovery News, USA Today (3 September 2009)