Scientists working in the desert badlands of northwestern Kenya have found stone tools dating back 3.3 million years, long before the advent of modern humans, and by far the oldest such artifacts yet discovered.
The tools, whose makers may or may not have been some sort of human ancestor, The Earth Institute (Columbia University) explains, push the known date of such tools back by 700 000 years.
Photos of selected Lomekwi 3 stones accompanying the paper show both cores and flakes knapped from the cores that the authors say illustrate various techniques.
“The whole site’s surprising, it just rewrites the book on a lot of things that we thought were true,” said geologist Chris Lepre of the Lamont-Doherty Earth Observatory and Rutgers University, a co-author of the paper who precisely dated the artifacts.
Chris Lepre from Lamont-Doherty Earth Observatory takes sediment samples to help date the age of the Lomekwi site. Credit: West Turkana Archaeological Project.
Lead author Sonia Harmand said that the tools ”shed light on an unexpected and previously unknown period of hominin behavior and can tell us a lot about cognitive development in our ancestors that we can't understand from fossils alone."
The researchers do not know who made these oldest of tools, but earlier finds suggest a possible answer: The skull of a 3.3-million-year-old hominin,Kenyanthropus platytops, was found in 1999 about a kilometer from the tool site. A K. platyopstooth and a bone from a skull were discovered a few hundred meters away, and an as-yet unidentified tooth has been found about 100 meters away.
Hominins are a group of species that includes modern humans, Homo sapiens, and our closest evolutionary ancestors. Anthropologists long thought that our relatives in the genus Homo – the line leading directly to Homo sapiens – were the first to craft such stone tools. But researchers have been uncovering tantalizing clues that some other, earlier species of hominin, distant cousins, if you will, might have figured it out.
The Lomekwi 3 dig sits in arid lands west of Lake Turkana in northwest Kenya. Credit: West Turkana Archaeological Project.
Lepre said a layer of volcanic ash below the tool site set a “floor” on the site’s age: It matched ash elsewhere that had been dated to about 3.3 million years ago, based on the ratio of argon isotopes in the material. To more sharply define the time period of the tools, Lepre and co-author and Lamont-Doherty colleague Dennis Kent examined magnetic minerals beneath, around and above the spots where the tools were found.
The Earth’s magnetic field periodically reverses itself, and the chronology of those changes is well documented going back millions of years. “We essentially have a magnetic tape recorder that records the magnetic field … the music of the outer core,” Kent said. By tracing the variations in the polarity of the samples, they dated the site to 3.33 million to 3.11 million years.
The find also has implications for understanding the evolution of the human brain. The toolmaking required a level of hand motor control that suggests that changes in the brain and spinal tract needed for such activity could have occurred before 3.3 million years ago, the authors said.
“This is a momentous and well-researched discovery,” said paleoanthropologist Bernard Wood of George Washington University, who was not involved in the study. “I have seen some of these artifacts in the flesh, and I am convinced they were fashioned deliberately.” Wood said he found it intriguing to see how different the tools are from so-called Oldowan stone tools, which up to now have been considered the oldest and most primitive.
Earlier dating work by Lepre and Kent helped lead to another landmark paper in 2011: a study that suggested Homo erectus, another precursor to modern humans, was using more advanced tool-making methods 1.8 million years ago, at least 300,000 years earlier than previously thought.
Featured image: The Lomekwi 3 dig sits in arid lands west of Lake Turkana in northwest Kenya. Credit: West Turkana Archaeological Project.