ROANOKE TIMES
Copyright (c) 1997, Roanoke Times
DATE: Thursday, January 23, 1997 TAG: 9701230050
SECTION: NATIONAL/INTERNATIONAL PAGE: A-6 EDITION: METRO
SOURCE: The Washington Post
THE PROBLEM IS, the discovery pushes back the date for tool-making by about 250,000 years - older than the oldest direct human ancestor.
Fossil hunters digging into a 2.5-million-year-old geological formation in Ethiopia have unearthed a horde of stone tools that they say are ``the oldest known artifacts from anywhere in the world.''
The find by Rutgers University researchers, reported in today's issue of the journal Nature, predates by as much as a quarter of a million years the earliest previous evidence of stone tool manufacture. It also is slightly earlier than the oldest incontestably dated fossils of the genus Homo - the evolutionary group to which modern man belongs.
That poses something of a problem, said Richard Potts, director of the human origins program at the Smithsonian Institution: ``We now have stone tools that are older than the scientific consensus'' about the earliest direct ancestors of human beings.
The discovery thus deepens what already was a profound mystery: What kind of creature first produced these implements? Was it, as most experts have argued, the immediate predecessors of Homo sapiens, whose superior mental capacity made tool use possible? Or could it have been some other member of the bipedal hominid family, such as the smaller-brained, bigger-toothed Australopithecus, a now-extinct group that lived in East Africa at the same time?
``We have not yet found [evidence of] the makers,'' said Sileshi Semaw of Rutgers, part of the team that uncovered and dated some 3,000 artifacts from the Gona River section of Ethiopia, and ``we don't rule out Australopithecus from making or using stone tools.''
No hominid fossils were found at the two Gona sites, although the general region is celebrated for its anthropological bounty.
Semaw and colleagues did their field work from 1992 to 1994 in the Gona area, where stone tools had been found - but not conclusively dated - as early as 1976. The researchers excavated the artifacts within a 4-inch-thick layer of earth, and then set about to establish the date of the layer by using two techniques.
One, called paleomagnetic dating, relies on the fact that the Earth's magnetic field reverses polarity (for unknown reasons) every few hundred thousand years. By examining the magnetic orientation of minerals in a rock sample, scientists found the excavation layer just below the tools was 2.6 million years old.
The other technique, which calculates how much of a radioactive isotope of potassium has decayed into a form of argon, indicated that the layer was no younger than 2.5 million years.
The tools discovered in Ethiopia consist of pieces of volcanic rock that have been fractured by hitting them with other rocks. The dislodged ``flakes'' could be used for scraping, cutting or chopping.
LENGTH: Medium: 60 lines ILLUSTRATION: PHOTO: AP. The fist-size core tool was a cobble from whichby CNBsharp flakes were chipped.