"The new date for Gademotta changes how we think about human evolution, because it shows how much more complicated the situation is than we previously thought," Basell said.
"It is not possible to simply associate specific species with particular technologies and plot them in a line from archaic to modern."
Gademotta was an attractive place for people to settle, due to its close proximity to fresh water in Lake Ziway and access to a source of hard, black volcanic glass, known as obsidian.
"Due to its lack of crystalline structure, obsidian glass is one of the best raw materials to use for making tools," Morgan explained.
In many parts of the world, archaeologists see a leap around 300,000 years ago in Stone Age technology from the large and crude hand-axes and picks of the so-called Acheulean period to the more delicate and diverse points and blades of the Middle Stone Age.
At other sites in Ethiopia, such as Herto in the Afar region northeast of Gademotta, the transition does not occur until much later, around 160,000 years ago, according to argon dating. This variety in dates supports the idea of a gradual transition in technology.
"A modern analogy might be the transition from ox-carts to automobiles, which is virtually complete in North America and northern Europe, but is still underway in the developing world," said study co-author Renne, who received funding for the Gadmotta analysis from the National Geographic Society's Committee for Research and Exploration. (The National Geographic Society owns National Geographic News.)
Morgan, of UC Berkeley, speculates that the readily available obsidian at Gademotta may explain why the technological revolution occurred so early there.
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