New minimum age determined for Homo sapiens in eastern Africa.
Ethiopia has long been a major focus of research into early human evolution. Back in the late 1960s, human fossils came to light in the Omo Kibish Formation in the country’s southwest (pictured). The discoveries came from an area of frequent volcanic activity. Here, archaeological finds and both animal and human fossils lie between layers of volcanic ash. The human fossils were thought to be less than 200,000 years old. However, they lay under a layer of volcanic ash that could not be dated accurately with the radiometric methods available at the time.
Over the past four years, a team led by Céline Vidal of Cambridge University has been trying to date all the major volcanic eruptions in the Ethiopian Rift dating to the Middle Pleistocene, the time when Homo sapiens first appeared in eastern Africa. The researchers uncovered samples of volcanic pumice, then ground them into microscopic size, which freed the minerals in them. This enabled them to identify the chemical signature of the volcanic glass that held the minerals together. The fingerprint of the thick volcanic layer under the Omo fossils linked them to the Shala volcano, also in Ethiopia, located more than 400km away. Pumice samples from the volcano dated to 230,000 years ago.
Since the Omo I fossils lay under the ash, they have to be more than 230,000 years old. This means 230,000 is the new minimum age for Homo sapiens in eastern Africa.
It is fully expected that the eastern African dates for Homo sapiens in Ethiopia will get pushed back yet further in the light of future discoveries. At the time of Omo 1, this was a landscape with abundant water, plenty of game and plant foods, also unlimited quantities of volcanic glass for making tools. More hominin finds are virtually certain.
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Image: The Omo Kibish Formation near the town of Kibish, where the early Homo sapiens fossils were found.
Credit: John Fleagle.