By Kate Ravilious | National Geographic News
Modern humans may have evolved more than 80,000 years earlier than previously thought, according to a new study of sophisticated stone tools found in Ethiopia.
The tools were uncovered in the 1970s at the archaeological site of Gademotta, in the Ethiopian Rift Valley. But it was not until this year that new dating techniques revealed the tools to be far older than the oldest known Homo sapien bones, which are around 195,000 years old.
Using argon-argon dating—a technique that compares different isotopes of the element argon—researchers determined that the volcanic ash layers entombing the tools at Gademotta date back at least 276,000 years.
Many of the tools found are small blades, made using a technique that is thought to require complex cognitive abilities and nimble fingers, according to study co-author and Berkeley Geochronology Center director Paul Renne.
Some archaeologists believe that these tools and similar ones found elsewhere are associated with the emergence of the modern human species, Homo sapiens.
“It seems that we were technologically more advanced at an earlier time that we had previously thought,” said study co-author Leah Morgan, from the University of California, Berkeley.
The findings are published in the December issue of the journal Geology.
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.
Complicated family tree
The lack of bones at Gademotta makes it difficult to determine who made these specialist tools. Some archaeologists believe it had to be Homo sapiens, while other experts think that other human species may have had the required mental capability and manual dexterity.
Regardless of who made the tools, the dates help to fill a key gap in the archaeological record, according to some experts.
“The new dates from Gademotta help us to understand the timing of an important behavioral change in human evolution,” said Christian Tryon, a professor of anthropology from New York University, who wasn’t involved in the study.
If anything, the story has now become more complex, added Laura Basell, an archaeologist at the University of Oxford in the U.K.
“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.”