Scientists Discover World's Oldest Stone Tools
Finds Challenge Ideas about Who Were the First Toolmakers
Sonia Harmand and Jason Lewis examine stone artifacts at the Lomekwi dig in Kenya. Credit: West Turkana Archaeological Project
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, push the known date of such tools back by 700,000 years; they
also may challenge the notion that our own most direct ancestors were
the first to bang two rocks together to create a new technology.
The discovery is the first evidence that an even earlier group of
proto-humans may have had the thinking abilities needed to figure out
how to make sharp-edged tools. The stone tools mark “a new beginning to
the known archaeological record,” say the authors of a new paper about
the discovery, published today in the leading scientific journal Nature.
“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.
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,” said lead
author Sonia Harmand, of the
Turkana Basin Institute at Stony Brook University and the Université Paris Ouest Nanterre.
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.
Chris Lepre from Lamont-Doherty Earth Observatory takes
sediment samples to help date the age of the Lomekwi site. Credit: West
Turkana Archaeological Project
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. platyops
tooth 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.
The precise family tree of modern humans is contentious, and so far, no one knows exactly how
K. platyops relates to other hominin species.
Kenyanthropus predates the earliest known
Homo
species by a half a million years. This species could have made the
tools; or, the toolmaker could have been some other species from the
same era, such as
Australopithecus afarensis, or an as-yet undiscovered early type of
Homo.
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.
Another co-author, Rhonda Quinn of Seton Hall University, studied
carbon isotopes in the soil, which along with animal fossils at the site
allowed researchers to reconstruct the area’s vegetation. This led to
another surprise: The area was at that time a partially wooded, shrubby
environment. Conventional thinking has been that sophisticated
tool-making came in response to a change in climate that led to the
spread of broad savannah grasslands, and the consequent evolution of
large groups of animals that could serve as a source of food for human
ancestors.
The Lomekwi 3 dig sits in arid lands west of Lake Turkana in northwest Kenya. Credit: West Turkana Archaeological Project
One line of thinking is that hominins started knapping – banging one
rock against another to make sharp-edged stones – so they could cut meat
off of animal carcasses, said paper co-author Jason Lewis of the
Turkana Basin Institute and Rutgers. But the size and markings of the
newly discovered tools “suggest they were doing something different as
well, especially if they were in a more wooded environment with access
to various plant resources," Lewis said. The researchers think the tools
could have been used for breaking open nuts or tubers, bashing open
dead logs to get at insects inside, or maybe something not yet thought
of.
“The capabilities of our ancestors and the environmental forces
leading to early stone technology are a great scientific mystery,” said
Richard Potts,
director of the Human Origins Program at the Smithsonian’s National
Museum of Natural History, who was not involved in the research. The
newly dated tools “begin to lift the veil on that mystery, at an earlier
time than expected,” he said.
Potts said he had examined the stone tools during a visit to Kenya in February.
“Researchers have thought there must be some way of flaking stone
that preceded the simplest tools known until now,” he said. “Harmand’s
team shows us just what this even simpler altering of rocks looked like
before technology became a fundamental part of early human behavior.”
Ancient stone artifacts from East Africa were first uncovered at
Olduvai Gorge
in Tanzania in the mid-20th century, and those tools were later
associated with fossil discoveries in the 1960s of the early human
ancestor
Homo habilis. That species has been dated to 2.1 million to 1.5 million years ago.
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.
Subsequent finds have pushed back the dates of humans’ evolutionary
ancestors, and of stone tools, raising questions about who first made
that cognitive leap. The
discovery of a partial lower jaw in the Afar region of Ethiopia, announced on March 4, pushes the fossil record for the genus
Homo to 2.8 million years ago. Evidence from recent papers, the authors note, suggests that there is anatomical evidence that
Homo had evolved into several distinct lines by 2 million years ago.
There is some evidence of more primitive tool use going back even
before the new find. In 2009, researchers at Dikika, Ethiopia, dug up
3.39 million-year-old animal bones marked with slashes and other cut
marks, evidence that someone used stones to trim flesh from bone and
perhaps crush bones to get at the marrow inside. That is the
earliest evidence of meat and marrow consumption by hominins.
No tools were found at the site, so it’s unclear whether the marks were
made with crafted tools or simply sharp-edged stones. The only hominin
fossil remains in the area dating to that time are from
Australopithecus afarensis.
The new find came about almost by accident: Harmand and Lewis said
that on the morning of July 9, 2011, they had wandered off on the wrong
path, and climbed a hill to scout a fresh route back to their intended
track. They wrote that they “could feel that something was special about
this particular place.” They fanned out and surveyed a nearby patch of
craggy outcrops. “By teatime,” they wrote, “local Turkana tribesman
Sammy Lokorodi had helped [us] spot what [we] had come searching for.”
By the end of the 2012 field season, excavations at the site, named
Lomekwi 3, had uncovered 149 stone artifacts tied to tool-making, from
stone cores and flakes to rocks used for hammering and others possibly
used as anvils to strike on.
The researchers tried knapping stones themselves to better understand
how the tools they found might have been made. They concluded that the
techniques used “could represent a technological stage between a
hypothetical pounding-oriented stone tool use by an earlier hominin and
the flaking-oriented knapping behavior of [later] toolmakers.”
Chimpanzees and other primates are known to use a stone to hammer open
nuts atop another stone. But using a stone for multiple purposes, and
using one to crack apart another into a sharper tool, is more advanced
behavior.
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.
Lepre, who has been conducting fieldwork in eastern Africa for about
15 years, said he arrived at the dig site about a week after the
discovery. The site is several hours’ drive on rough roads from the
nearest town, located in a hot, dry landscape he said is reminiscent of
Arizona and New Mexico. Lepre collected chunks of sediment from a series
of depths and brought them back to Lamont-Doherty for analysis. He and
Kent used a bandsaw to trim the samples into sugar cube-size blocks and
inserted them into a magnetometer, which measured the polarity of tiny
grains of the minerals hematite and magnetite contained in the sediment.
“The magnetics pretty much clinches that the age is something like
3.3 million years old,” said Kent, who also is a professor at Rutgers.
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.
