A research team from the Nagoya University Museum and Graduate School of Environmental Studies in Japan has revealed the different physical properties of rocks used by humans during the Early Paleolithic. Their research shows that these ancient humans considered a variety of factors when choosing rocks, not just whether the rock would break easily. The discovery means early humans had the technical expertise to identify the rocks best suited for their tools. The team's findings were recently published in the Journal of Paleolithic Archeology.
Investigations into the mechanical properties of rocks suggest that Paleolithic humans altered their choice of raw materials to suit their stone tool morphology and production techniques. Source: EikiSuga (Photography), ReikoMatsushita (Illustrations and Design)
When Homo sapiens migrated from Africa into Eurasia, they used stone tools made from rocks such as obsidian and flint to cut, slice and craft long-range weapons. Because stone tools play an important role in human culture, understanding how early humans made them is important to archaeologists.
Key Research in Southern Jordan
Since the geographical expansion of Homo sapiens in Eurasia began in the Middle East, archaeologists Eiki Suga and Seiji Kadowaki of Nagoya University focused on prehistoric sites belonging to three epochs in the Jebel Kalka region of southern Jordan. The research team analyzed flint nodules that were mined during the Middle and Upper Paleolithic periods (70,000 to 30,000 years ago).
They believe that Paleolithic humans knew which rocks were suitable for making tools and therefore intentionally sought them out. According to their hypothesis, Paleolithic humans intentionally sought out translucent, smooth flint because such flint could be easily broken from rock walls and create sharp edges.
The team used Schmidt hammers and Rockwell hardness testers to test the mechanical properties of the rocks. Schmidt hammers measure the elastic behavior of a material after a hammer strikes it, which tells researchers the material's rebound hardness. The Rockwell hardness tester presses a diamond indenter against the rock surface to test the rock's strength.
Initially, as Suga and Kadowaki expected, they found that fine-grained chert requires less breaking force than medium-grained chert. This makes fine-grained chert more attractive for making small stone tools. In fact, many stone tools from the Upper Paleolithic (40,000 to 30,000 years ago) contain fine-grained flint.
Revisit assumptions and understand choices
However, an earlier study by the same research team found that during the Middle to Upper Paleolithic and Early Paleolithic (70,000 to 40,000 years ago), medium-grained flint was more commonly used to make stone tools than fine-grained flint. But if fine-grained flint is so easy to work with, why didn't our ancestors make all their tools from fine-grained flint?
After further investigation, the researchers found that most of the fine-grained chert in the area had a large number of internal cracks due to geological activity, making it unsuitable for making large stone tools such as Levallois artifacts and strong blades.
Therefore, Paleolithic humans appear to have selected medium-grained flint for making large tools, even though this material is difficult to transform into tools because it is more likely to be durable. This provides a fascinating look into the behavior of our ancestors, as they selected flint based not just on its brittleness but on many other factors, and they were able to discern which rocks were best for making stone tools from.
Suga is enthusiastic about these findings because they illustrate the complexity of our ancestors' behavior. He said: "This study shows that Paleolithic humans changed their choice of raw materials to adapt to their stone tool morphology and production technology. We believe that these prehistoric humans had a perceptual understanding of the properties of rocks and intentionally selected the stones to use based on the required stone tool morphology and production technology. This intentional selection of stone raw materials may be an important component of stone tool production. This may in some aspects show flexible technological behavior to adapt to the environment."
"There are still many unanswered questions about why living humans expanded their distribution between 50,000 and 40,000 years ago. Recently, ancient DNA analysis has shown that modern humans (Homo sapiens) interacted and interbred with Neandertals and Denisovans. However, ancient DNA cannot tell us the actual historical events and how they happened," Suga said. "If we want to know what happened to allow Homo sapiens to thrive, we need to study cultural remains, such as stone tools excavated from archaeological sites. This resource use is an important record that illuminates the evolution of human technological behavior, environmental adaptation, and population growth at that time."
Reference "Reasons for the increase in early Paleolithic 'fine stone tools' in southern Jordan: Eiki Suga, Kazuhiro Tsukada, Oday Tarawneh, Sate Massadeh and Seiji Kadowaki, 8 November 2023, Journal of Paleolithic Archeology."
DOI:10.1007/s41982-023-00164-w
Compiled source: ScitechDaily