Researchers are using highly precise chemical analysis and artificial intelligence to determine the likely source of stones from which ancient humans created flint hand axes some 750,000 years ago, according to a recent article in the journal Geoarchaeology. The new technology has allowed archaeologists to conclude that early humans in the Galilee region traveled more than a day to get a specific type of stone flint to make hand axes, showing that Homo Erectus had the ability to plan complex journeys and share information across generations.
“Often, the level of sophistication about planning and knowledge transference between generations is not highly appreciated or taken as human capabilities during these periods,” explained Dr. Meir Finkel of Tel Aviv University, one of the lead researchers on the study.
The researchers determined that the hand axes found in two Acheulian sites, Gesher Banot Yaakov and Ma’ayan Barukh, located north of the Sea of Galilee, were likely created from stone in the Dishon streambed, which was located around a day’s walk from the sites, with an elevation climb of over 750 meters (2,500 feet). Acheulian refers to a time during the Paleolithic period, some 1.7 million years ago to 200,000 years ago, when early humans mastered the art of creating stone tools, especially hand axes and cleavers.
“What we succeeded to show from a geochemical perspective and the issue of the amount of stone is that they were walking up a mountain, 20 kilometers [12.4 miles] and 750 meters up just in one way, and they had to plan it,” said Finkel.
Apple that falls far from the tree
There are two types of technology that helped the researchers to identify the place where Homo Erectus excavated the flint some 750,000 years ago.
First, the researchers from Tel Aviv University, Tel Hai Academic College and the Geological Survey of Israel removed parts of 10 hand axes from each of the two sites and ground them into a fine powder so they could be examined by mass spectrometry, a type of analysis that identifies the individual elements in a sample.
“You get amazing results from this, the detection is up to parts per billion,” said Finkel.
This allowed the team to see the equivalent of a unique chemical thumbprint of each hand ax for 40 different elements. The information allowed them to match the stone to the geologic layer, or the time period when the stone was originally created. They determined the hand axes were from the Eocene Epoch, and the stone was deposited on the sea bed some 60 million years ago, said Dr. Yoav Ben Dor, a researcher in the geochemistry department at the Geological Survey of Israel, and another author of the study.
By looking at maps, they identified that the Dishon streambed had exposed rocks from the Eocene Epoch, and when they tested these stones, the chemical thumbprint was similar, confirming their theory.
There’s only one or two mass spectrometers in Israel, including the one at Tel Aviv University, and the practice of using them for archaeology work has only gained popularity in the past few years, said Finkel.
The real novelty of the experiment was not in the chemical analysis, but in the researcher’s ability to identify the area or even the exact stone where it originated, Finkel said.
“We developed a dedicated algorithm based on several computational steps, alongside machine learning models,” said Ben Dor. “We were able to stick [information about the hand axes] into machine learning models and use them to predict where they came from.”
Ben Dor said that as the technology improves, they may even be able to identify the exact stones from which the hand axes were knapped. Flint knapping is a method of carving a stone tool from flint rock, using another rock to chip off flakes until the desired shape is achieved.
The researchers collected around 150 samples of rocks from around the two archaeological sites. Using the algorithm, they determined that the flint was likely excavated from the Dishon streambed, some 20 kilometers (12.5 miles) away.
Even in the past year and a half that the researchers have been using the combination of mass spectrometer and algorithm, they’ve been seeing more accurate results.
“The machine learning is getting better and better all the time as we’re adding more and more flint examples,” said Finkel.
Archaeologists are also sending the team rock samples from across Israel, creating a robust database that could eventually determine the specific group of boulders or geographic area where stone tools were created. This could unlock information about trade routes and collaboration that has previously been unknown.
“This is the cutting edge of mathematics used in archaeology,” said Finkel, whose area of expertise is researching raw material sources in prehistoric times. “I believe the archaeological world will begin to use it more and more… this method of comparing archaeological items to raw materials is the most advanced statistical capability used today.”
“People are now beginning to send me items [to analyze] and asking me to come to excavations and have a look, and our database is growing all the time,” he said.
‘Sometimes you have to destroy to get answers’
Previously, the understanding about prehistorical tool creation is that they were made from flint stones that Homo Erectus stumbled across as they were doing other activities, such as fetching water or hunting, Finkel explained.
“The new thing is we can show that 750,000 years ago, humans were preplanning their activities and putting a lot of effort, probably, into expedition groups that went to bring the right material and it likely took a few days,” said Finkel.
It was likely at least a three-day journey — a day to travel there, a day working to chip away pieces of the flint for the axes, which were mostly created at the Dishon site, and a day to return.
The Dishon site has dozens of tons of discarded stone chips that show that the site was likely used to create stone tools for tens of thousands of years. In a single tailing or discard pile that Finkel excavated a few years ago, there were a quarter of a million flint chips that weighed around 20 tons, and there are many piles of comparable size at Dishon, he said.
Knowledge about the site was clearly passed from generation to generation, illustrating complex social patterns and communication, explained Finkel. Archaeologists have discovered some 3,500 hand axes in Ma’ayan Barukh and hundreds more in Gesher Banot Yaakov.
Thousands of the hand axes are on display to the public at the Upper Galilee Museum of Prehistory at Kibbutz Ma’ayan Barukh. Previously, archaeologists have uncovered remains of hunted elephants at Ma’ayan Barukh, and this study further supports the theory that means that early humans were capable of organizing complex expeditions to gather materials and hunt as a group, said Finkel.
One of the challenges is that researchers had to destroy parts of the hand ax in order to complete the tests, which is the most accurate chemical analysis available. They needed about 30 to 50 grams of each hand ax for the mass spectrometry testing.
“I was standing behind Dr. Gonen Sharon from Tel Hai when he was breaking off pieces, and I could tell it was hard for him,” said Finkel. “You can see in the photos how beautiful the hand axes are… But sometimes you have to destroy something in order to get some answers.”
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