A publication of the Archaeological Institute of America
More than 2,600 sharp-edged flakes, flake fragments, and cores (cobbles from which flakes have been removed), found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia, have been dated to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the known date at which humans were making stone tools.
Excavated between 1992 and 1994 by Rutgers University paleoanthropologists Sileshi Semaw and John W.K. Harris at three sites along the Gona River, the artifacts are similar in type to the 1.8-million-year-old tools found by Mary Leakey at Olduvai Gorge, Tanzania, in the 1960s. Known as Oldowan, the tool type has been found at other East African sites: Omo in southern Ethiopia, Lokalalei in northern Kenya, and Hadar, five miles east of the Gona River study area. Until now the oldest known examples were dated to 2.3 to 2.4 million years ago.
Because no hominid remains were found in association with the tools and they predate the oldest known remains of the genus Homo (see ARCHAEOLOGY, January/February 1997), the find has left the identity of the makers open to speculation. Semaw and his team will return to the field later this year in hopes of answering this question.
Using the argon/argon dating method on a layer of volcanic ash nearly seven feet above the tool-bearing deposit, Paul Renne of the Berkeley Geochronology Center determined that the Gona artifact assemblage was more than 2.52 million years old. A maximum date of 2.6 million years ago was obtained for mineral-rich sediments just below the artifacts using paleomagnetic dating.