考古学：エチオピアで出土した最古のヒト化石の年代推定の精度が高まった

The remains of the Kibish Omo I from Ethiopia — among the oldest known fossils of Homo sapiens in eastern Africa — could be at least 36,000 years older than previously thought, according to a paper published in Nature. The minimum age is estimated to be approximately 233,000 years old, a timescale that aligns more consistently with models of modern human evolution.

The Omo I has previously been predicted to be around 197,000 years old. However, this estimate, which was made by studying layers of ash corresponding to the timing of volcanic eruptions, has been challenged. Céline Vidal and colleagues re-examined the layer of volcanic ash that overlies the sediment containing Omo I, linking the volcanic deposits to a major explosive eruption of the Shala volcano in the Main Ethiopian Rift. These analyses allowed the authors to more precisely date the age of the Omo fossils below this layer, to approximately 233,000 (±22,000) years old. This new age corresponds with most models of modern human evolution, which predict that our species originated and diverged from our closest ancestors around 350,000 to 200,000 years ago.

The authors conclude that future research will be needed to obtain a robust maximum age for Omo I. Further analyses will also hopefully confirm the age of the Herto fossils — additional early H. sapiens fossils from Ethiopia, generally reported to be between 160,000 and 155,000 years old — as these are shown to lie underneath a different volcanic ash layer to that of the Omo fossils, contrary to previous understanding.