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TOOL TIMEÂ Researchers study sediments in Ethiopia where sharp-edged stone tools dating to around 2.6 million years ago were found. Rocks placed over excavated areas protected fragile sediment.
Discoveries in East Africa of what may be the oldest expertly sharpened stone implements suggest that early members of the human genus, Homo, invented these tools by around 2.6 million years ago, researchers say. But their conclusions are controversial.
New finds at a site in Ethiopia called Ledi-Geraru fit a scenario in which various early Homo groups devised ways to sharpen handheld stones, assert archaeologist David Braun of George Washington University in Washington, D.C., and his colleagues. Ledi-Geraru artifacts date to between 2.58 million and 2.61 million years ago, the team reports online June 3 in the Proceedings of the National Academy of Sciences.
Another team previously had unearthed sharpened stones that were 2.55 million to 2.58 million years old at Gona, a nearby Ethiopian site (SN: 4/17/04, p. 254). Until now, those were the oldest examples of cutting and digging devices with systematically sharpened edges. Archaeologists refer to these types of artifacts as Oldowan tools because the first examples were found at East Africaâs Olduvai Gorge.
Age estimates for Ledi-Geraru artifacts were determined by where they were found, between a dated layer of volcanic ash and sediment preserving a known reversal of Earthâs magnetic field. Stone tools at Ledi-Geraru âare probably at least 50,000 years older, but could be up to 100,000 years older than Gona artifacts,â Braun says. His team recovered 300 stone artifacts, including sharp-edged rocks and larger rocks from which those implements were struck. Those finds were strewn among 330 fossilized bones of nonhuman animals.
One of the oldest known sharpened tools, unearthed in Ethiopia, is shown here from different angles in photographs, top, and 3-D computer models, bottom.
Older stone tools have been discovered. For instance, large stone implements found in Kenya at a site called Lomekwi 3, many perhaps best suited for pounding objects, may date to 3.3 million years ago (SN: 6/13/15, p. 6). Contested evidence, based on possible stone-tool incisions on two 3.4 million-year-old animal bones, suggests that Australopithecus afarensis, ancient hominids best known for Lucyâs partial skeleton, butchered animals before the Homo genus appeared (SN: 9/11/10, p. 8). And present-day chimps and monkeys crack open nuts with stones, a sign that such behavior extends far back in primate evolution (SN: 11/26/16, p. 16).
But the Ledi-Geraru artifacts indicate that Homo, which possibly originated around 2.8 million years ago based on a jaw already found at Ledi-Geraru (SN: 4/4/15, p. 8), took stone-tool making to a new level characterized by skilled edge sharpening, Braunâs group argues.
Archaeologist Ignacio de la Torre of University College London, who did not participate in the new study, agrees. âThe association of Oldowan tools with early Homo may be best explained by shifts in diet and access to animal meat through scavenging,â he says.
Animal bones unearthed with the Ledi-Geraru artifacts came from creatures such as gazelles and giraffes that would have inhabited open grasslands with few trees, Braunâs team says. That landscape likely presented frequent scavenging opportunities, the researchers suspect. Lucyâs species would have spied fewer fresh animal carcasses, they contend, because the same part of East Africa featured shrubs with occasional stands of trees and forested areas during her time period.
An ability to cut meat and other food with stone tools may have influenced a transition to smaller teeth observed in early Homo specimens, Braunâs group holds.
No stone tools dating to between 3.3 million and 2.6 million years ago have been found, so itâs unclear if Ledi-Geraru artifacts represented a rapid change in toolmaking or an elaboration of earlier techniques, says archaeologist Sonia Harmand of Stony Brook University in New York. Sharp-edged flakes struck from larger rocks have been found at Kenyaâs Lomekwi 3, so precursors of Oldowan techniques might have started developing as early as 3.3 million years ago, says Harmand, who directed Lomekwi 3 excavations.
ANCIENT FLYOVER A drone provides a panoramic tour of Ethiopiaâs Ledu-Geraru site and the spot where scientists unearthed what they say are the oldest known stone tools with sharpened edges.
Other researchers doubt both Braunâs and Harmandâs conclusions. Ledi-Geraru discoveries add to an increasingly confusing picture of early stone-tool making, says archaeologist Manuel DomÃnguez-Rodrigo of Complutense University in Madrid. Until a detailed analysis of sediment formation at the Ledi-Geraru site is published, he is skeptical of the claim that the newly discovered artifacts were found where they were originally deposited or are as old as reported. Similarly, DomÃnguez-Rodrigo suspects that Harmandâs Lomekwi 3 artifacts originally lay in much younger sediment before erosion and water moved them down a slope to 3.3 million-year-old sediment. And animal trampling likely created the reported incisions on animal bones from Lucyâs time, he argues.
Ledi-Geraru artifacts were also found on a slope where they could originally have lain in sediment from after 2.6 million years ago, says archaeologist Yonatan Sahle of the University of TÃ¼bingen in Germany. Sahle participated in previous fieldwork at Ledi-Geraru with Braunâs group, but isnât part of the new paper. Itâs âsimply unwarrantedâ to tag stone tools excavated at Ledi-Geraru as the earliest Oldowan specimens without a more thorough sediment analysis, Sahle contends. Even the evolutionary identity and age of the Ledi-Geraru jaw initially assigned to Homo are up for grabs, he says.
Microscopic study of Ledi-Geraru sediment indicates that stone artifacts were dropped at the edge of a lake and quickly covered by earth that held the finds in their original positions, Braun says.
For now, scientistsâ clashing positions on the reliability and implications of ancient toolmaking evidence also appear held in place, if not etched in stone.
D.R. Braun et al. Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity. Proceedings of the National Academy of Sciences. Published online June 3, 2019. doi:10.1073/pnas.1820177116. Â
B. Bower. Wild monkeys throw curve at stone-tool makingâs origins. Science News. Vol. 190, November 26, 2016, p. 16. Â
B. Bower. Earliest known stone tools unearthed in Kenya. Science News. Vol. 187, June 13, 2015, p. 6. Â
B. Bower. Ancient jaw may hold clues to origins of human genus. Science News. Vol. 187, April 4, 2015, p. 8.
B. Bower. Lucyâs kind used stone tools to butcher animals. Science News. Vol. 178, September 11, 2010, p. 8.
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