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The Oldowan Stone tool industry was named for 1.8-million-year-old (Myr) artefacts found near the bottom of Olduvai Gorge, Tanzania. Subsequent archaeological research in the Omo (Ethiopia) and Turkana (Kenya) also yielded stone tools dated to 2.3 Myr. Palaeoanthropological investigations in the Hadar region of the Awash Valley of Ethiopia1, revealed Oldowan assemblages in the adjacent Gona River drainage2. We conducted field work in the Gona study area of Ethiopia between 1992 and 1994 which resulted in additional archaeological discoveries as well as radio-isotopic age control and a magnetic polarity stratigraphy of the Gona sequence. These occurrences are now securely dated between 2.6–2.5 Myr. The stone tools are thus the oldest known artefacts from anywhere in the world. The artefacts show surprisingly sophisticated control of stone fracture mechanics, equivalent to much younger Oldowan assemblages of Early Pleistocene age. This indicates an unexpectedly long period of technological stasis in the Oldowan.

Recent investigations of Lower Pleistocene sites at Chesowanja have yielded in situ Oldowan and Oldowan-like stone artefacts, evidence of fire and a fragmentary 'robust' australopithecine cranium. Burnt clay found at one artefact locality dated to >1.42±0.07 Myr is the earliest known evidence of fire associated with a hominid occupation site.

A survey of Ethiopia's Middle Awash Valley in 1981 yielded new and significant archaeological, palaeontological, geological and geochronological results. Included in the new discoveries are hominid fossils from the Pliocene which show primitive cranial anatomy and a femur adapted to bipedality. Archaeological records document human technological change spanning the past 1.5 Myr.