Paleolithic humans may have understood the properties of rocks for making stone tools

A research group led by the Nagoya University Museum and Graduate School of Environmental Studies in Japan has clarified differences in the physical characteristics of rocks used by early humans during the Paleolithic. They found that humans selected rock for a variety of reasons and not just because of how easy it was to break off. This suggests that early humans had the technical skill to discern the best rock for the tool. The researchers published the results in the Journal of Paleolithic Archaeology.

As Homo sapiens moved from Africa to Eurasia, they used stone tools made of rocks, such as obsidian and flint, to cut, slice, and craft ranged weapons.

Because of the significant role they played in their culture, understanding how early humans made stone tools is important to archaeologists.

Since the geographic expansion of Homo sapiens in Eurasia started in the Middle East, archaeologists Eiki Suga and Seiji Kadowaki from Nagoya University focused on the prehistoric sites belonging to three chronological periods in the Jebel Qalkha area, southern Jordan.

The team analyzed flint nodules in the outcrops that were exploited during the Middle and Upper Paleolithic (70,000 to 30,000 years ago).

They believe Paleolithic humans understood which rocks were appropriate for making tools and, therefore, intentionally searched for them.

According to their hypothesis, Paleolithic humans intentionally searched for flint that was translucent and smooth, as it could be easily broken off the rock face and shaped into sharp edges.

The group used a Schmidt Hammer and a Rockwell Hardness Device to test the mechanical properties of the rocks.

The Schmidt Hammer measures the elastic behavior of a material after the hammer strikes it, which tells researchers its rebound hardness.

The Rockwell hardness device presses a diamond indenter on the rock surface to test its strength.

At first, as Suga and Kadowaki expected, fine-grained flint was found to require less force to fracture than medium-grained flint.

This would have made the fine-grained flint more attractive in producing small stone tools.

Indeed, many stone tools from the Early Upper Paleolithic (40,000 to 30,000 years ago) contain fine-grained flint.

However, an earlier study by the same team found that during the Late Middle Paleolithic and the Initial Upper Paleolithic (70,000 to 40,000 years ago), medium-grained flint was more commonly used in stone tools than fine-grained flint.

But if fine-grained flint was so easy to use, why did our ancestors not make all their tools from it?

On further investigation, the researchers found that much of the fine-grained flint in the area suffered from abundant internal fractures caused by geological activities, which would have made it unsuitable for large stone tools, such as Levallois products and robust blades.

Therefore, it seems that Paleolithic humans selected the medium-grained flint for large tools, even though it was a tough material to modify into tools, as it was more likely to last longer.

This offers a fascinating insight into our ancestors' behavior, as they selected flint based on many factors other than just how easy it was to fracture and could discern the most suitable rock to use to make stone tools.

Suga is enthusiastic about the findings, which suggest the complexity of our ancestors' behaviour.

"This study illustrates that the Paleolithic humans changed their choice of raw material to suit their stone tool morphologies and production techniques," he said.

"We believe that these prehistoric humans had a sensory understanding of the characteristics of the rocks and intentionally selected the stone material to be used according to the form and production technique of the desired stone tools. This intentional selection of the lithic raw material may have been an important component of the production of stone tools. This may show some aspect of flexible technological behavior adapted to the situation."

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Solar flare throws light on ancient trade between the Islamic Middle East and the Viking Age

Mobility shaped the human world profoundly long before the modern age. But archaeologists often struggle to create a timeline for the speed and impact of this mobility. An interdisciplinary team of researchers at the Danish National Research Foundation's Centre for Urban Network Evolutions at Aarhus University (UrbNet) has now made a breakthrough by applying new astronomical knowledge about the past activity of the sun to establish an exact time anchor for global links in the year 775 CE.

In collaboration with the Museum of Southwest Jutland in the Northern Emporium Project, the team has conducted a major excavation at Ribe, one of Viking-age Scandinavia's principal trading towns. Funded by the Carlsberg Foundation, the dig and the subsequent research project were able to establish the exact sequence of the arrival of objects from various corners of the world at the market in Ribe. In this way, they were able to trace the emergence of the vast network of Viking-age trade connections with regions such as North Atlantic Norway, Frankish Western Europe and the Middle East. To obtain a chronology for these events, the team has pioneered a new use of radiocarbon dating.

New use of radiocarbon dating

"The applicability of radiocarbon dating has hitherto been limited due to the broad age ranges of this method. Recently, however, it has been discovered that solar particle events, also known as Miyake events, cause sharp spikes in atmospheric radiocarbon for a single year. They are named after the female Japanese researcher Fusa Miyake, who first identified these events in 2012. When these spikes are identified in detailed records such as tree rings or in an archaeological sequence, it reduces the uncertainty margins considerably," says lead author Bente Philippsen.

The team applied a new, improved calibration curve, based on annual samples, to identify a 775 CE Miyake event in one floor layer in Ribe. This enabled the team to anchor the entire sequence of layers and 140 radiocarbon dates around this single year.

"This result shows that the expansion of Afro-Eurasian trade networks, characterised by the arrival of large numbers of Middle Eastern beads, can be dated in Ribe with precision to 790±10 CE -- coinciding with the beginning of the Viking Age. However, imports brought by ship from Norway were arriving as early as 750 CE," says Professor Søren Sindbæk, who is also a member of the team.

This groundbreaking result challenges one of the most widely accepted explanations for maritime expansions in the Viking Age -- that Scandinavian seafaring took off in response to growing trade with the Middle East through Russia. Maritime networks and long-distance trade were already established decades before impulses from the Middle East caused a further expansion of these networks.

The construction of the new, annual calibration curve is a global effort to which the researchers from UrbNet and the Aarhus AMS Centre at the Department of Physics and Astronomy at Aarhus University have contributed.

"The construction of a calibration curve is a huge international effort with contributions from many laboratories around the world. Fusa Miyake's discovery in 2012 has revolutionized our work, so that we now work with annual time resolution. New calibration curves are recurrently released, most recently in 2020, and Aarhus AMS centre has contributed significantly. The new high-resolution data from the present study will enter into a future update of the calibration curve and thus contribute to improve the precision of archaeological dates worldwide. This will provide better opportunities to understand rapid developments such as trade flows or environmental change in the past," says Jesper Olsen, Associate Professor at Aarhus AMS Centre.

The global trends revealed by the study are essential for the archaeology of trading towns like Ribe. "The new results enable us to date the influx of new artefacts and far-reaching contacts on a much better background. This will help us to visualise and describe Viking Age Ribe in a way that will have great value for scientists, as well as helping us to present the new insight to the general public," says Claus Feveile, curator of the Museum of Southwest Jutland.

Background facts

One of the most spectacular episodes of pre-modern global connectivity happened in the period c. 750-1000 CE, when trade with the burgeoning Islamic empire in the Middle East connected virtually all corners of Afro-Eurasia.

The spread of coins, trade beads and other exotic artefacts provides archaeological evidence of the trade links stretching from Southeast Asia and Africa to Siberia and the northernmost corners of Scandinavia. In the north, these long-distance connections mark the beginning of the maritime adventures that define the Viking Age. Researchers have even suggested that it was the arrival of silver and other valuable objects via Eastern Europe which sparked the first Scandinavian Viking expeditions.

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