An Israeli research team has caught our ancestors in the act of learning to mine raw materials for tools. The discovery suggests that some cave-dwellers were mining flint 300,000 years ago, while their neighbours were still using whatever stones were lying around.

Flint is a hard, brittle rock that flakes easily to form sharp edges for primitive knives or axes. Tools made from it have been around for some 2.5 million years. But because exposed rock tends to be cracked or weathered, flint from beneath the surface makes superior tools.

So when did our ancestors first learn to mine better flint? To investigate, the researchers compared the chemical compositions of a range of 300,000-year-old tools from prehistoric Israel. They were looking for an isotope called beryllium-10, which is produced when cosmic rays that strike the Earth from space react with the silicon dioxide in rock.

Tools fashioned from surface flint should have higher levels of beryllium-10 than those mined from underground, explains Elisabetta Boaretto of the Weizmann Institute of Science in Rehovot, who led the study. This is because buried rocks would have been shielded from cosmic rays for millions of years before they were dug up.

Flint blades from Tabun Cave near present-day Haifa in northern Israel have beryllium-10 levels that indicate they were made from mined flint, the researchers report in Proceedings of the National Academy of Sciences¹. But tools found in Qesem Cave, barely 100 kilometres to the south, bore the hallmarks of surface rock.

Because the tools are the same age, the result shows that early humans living at Tabun were choosier about their raw materials, Boaretto argues. "It indicates a conscious action to recover material rather than just randomly picking it up off the ground," she says.

The theory tallies with the increasing sophistication of human tools a few hundred thousand years ago, says Daniel Lieberman, an anthropologist at Harvard University in Cambridge, Massachusetts. At some point, early humans made a transition, ditching crude shards of flint in favour of specially shaped rocks from which a delicate blade could be created with a single, well-aimed blow.

Although experts do not know the exact date of this transition, the Israeli team may have opened a window on it, says Lieberman. "It makes sense; they could have been going after high-quality flint for particular uses."

It is not clear what mining methods the Tabun cavemen would have used, admits Boaretto. They may have had to burrow through a metre or more of sediment, but that does not rule out the possibility that the miners worked with bare hands. "It's not trivial," she says. "With some work I imagine you could get it out."

Verri, G. et al. Proc. Natl Acad. Sci. USA, published online, doi:10.1073/pnas.0402302101, (2004). |Article|

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