In the 1970s, a group of sophisticated stone tools were unearthed at Gademotta, in the Ethiopian Rift Valley. Researchers who studied them employed the dating techniques available to them at that time, and dated them as having been crafted nearly 200,000 years ago.
But a recent study, by the Berkeley Geochronology Center, recently examined the tools using argon-argon dating―a modern technique that compares different isotopes of the element argon. Scientists determined that the volcanic ash layers coating the Gademotta tools date back at least 276,000 years.
The findings, which are published in the latest issue of the journal Geology, says that the bones of the oldest known homo sapiens are around 195,000 years old. Therefore, the tools found at Gademotta clearly indicate that humans have existed for more than 80,000 years longer than archaeologists previously thought.
Some researchers believe that the Gademotta tools and others found elsewhere are closely linked to the emergence of the modern human species. Many of the tools are simple, small blades, crafted using techniques that require nimble fingers, dexterity, and complex thought processes.
According to one of the study's authors, Leah Morgan, it seems that we were technologically more advanced at an earlier time than we had previously assumed.
Gademotta, located close to fresh water in Lake Ziway, was a popular place for people to settle. The area is a good source of black volcanic glass known as obsidian, which is one of the best raw materials used for making tools.
Morgan speculates that the ease of obtaining obsidian at Gademotta might explain why the technological revolution occurred earlier in that location than in other sites in Ethiopia where the transition in technology occurred much later, around 160,000 years ago.
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, feels co-author Renne, who received funding for the Gademotta analysis from the National Geographic Society's Committee for Research and Exploration.
No bones were found at the Gademotta site, which makes it difficult to determine who made these sophisticated tools. Although many archeologists believe they had to have been created by homo sapiens, other experts think that there may have existed another human species that had the mental and manual capabilities to design such tools.
But no matter who made the tools, the new dating methods make it easier to fill in an important gap in the archaeological record.
Laura Basell, an archaeologist at London's University of Oxford, posits that the story of human evolution has now become even more complex and it is not possible to simply associate specific species with particular technologies and plot them in a line from archaic to modern.
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 had thought.