Solving the mystery of limestone balls carved by humans 1.4 million years ago

Archaeologists have long puzzled over the purpose of tens of thousands of roughly hewn limestone balls scattered across areas where early humans lived. Some of these artifacts date back to as early as 2.5 million years ago and are found nearly everywhere that people existed.

For the first time, researchers from Hebrew University have utilized advanced 3D mapping technology to determine that early humans purposefully carved these limestone spheroids. This discovery brings scientists a step closer to understanding these mysterious objects.

These spheroids first emerged in East Africa during the Oldowan era, the earliest part of the Stone Age, about 2.5 million years ago. These carved rock balls spread across northern Africa, the Middle East, and Europe, continuing to be produced until the Middle Paleolithic Age, around 30,000 years ago. Despite their prevalence at Stone Age archaeology sites, their purpose has remained elusive.

Researchers from Hebrew University, in collaboration with Tel Hai College in northern Israel and Rovira i Virgili University in Spain, analyzed a collection of 150 limestone spheroids from the ‘Ubeidiya archaeological site near the Dead Sea.

The ‘Ubeidiya site is significant as it contains the earliest known evidence of humans during the Acheulian period outside of Africa.

The Acheulian period, part of the Paleolithic era, spans from about 1.7 million years ago to 200,000 years ago and is characterized by early humans mastering stone tool creation, particularly hand axes and cleavers. The ‘Ubeidiya spheroids were carved around 1.4 million years ago.

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Using state-of-the-art 3D analysis methods, including spherical harmonics and surface curvature, researchers concluded that early humans employed a “premeditated reduction strategy” to create these spherical objects, a process known as knapping.

“We noted that almost all of the spheroids from ‘Ubeidiya, even the nearly perfectly spherical ones, still had a flat area on their surface,” explained Antoine Muller, a PhD candidate at Hebrew University. “The spherical harmonics analysis helped us identify these surfaces and confirm that this was a repeated pattern, not just in our imagination. These flat surfaces likely served as striking platforms to help shape the spheroids.”

Muller, the lead author of the study published in Royal Society Open Science, is part of the Computational Archaeology Laboratory at Hebrew University of Jerusalem, directed by Prof. Leore Grosman.

The researchers have made their dataset available online to aid other archaeologists studying spheroids worldwide. While the ‘Ubeidiya spheroids are about 1 million years younger than those discovered in parts of eastern Africa, the understanding that these objects were intentionally created could change how archaeologists view these artifacts globally.

“If similar intentional shaping can be demonstrated on Oldowan spheroids, this would likely represent the earliest evidence of hominins imposing a desired symmetrical geometry on their tools,” the researchers wrote.

The use of 3D mapping marks a significant step toward understanding these widespread spheres, but much remains to be discovered. “Unfortunately, it is still unclear what the spheroids may have been used for,” said Muller. “Narrowing down their functionality will require a lot more work.”

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