Were the limestone spheroids of 'Ubeidiya intentionally designed?

Ancient limestone spheroids from 'Ubeidiya, about three kilometers south of the Kinneret in the Jordan Valley, were intentionally crafted by early hominins – challenging previous assumptions about these enigmatic objects. A new study led by Hebrew University (HU) archaeologists offers fresh insights into early-human capabilities.

Limestone spheroids, enigmatic lithic artifacts from the ancient past, have perplexed archaeologists for years. Spheroids are ball-shaped stone objects found in African archaeological sites dating from 1.8 million years ago (the Early Stone Age) to at least 70,000 years ago (the Middle Stone Age). 

Spheroids are either handmade or naturally shaped stones chosen and transported to places where they are used, making them one of the longest-used technologies on record. Most hypotheses about their use hypothesized that they were tools made by being struck, for shaping or grinding other materials, but their size and round shape made them potentially useful as projectile weapons, a property that – uniquely – humans have been specialized to exploit for millions of years. 

‘Ubeidiya is an archaeological site of the early Pleistocene era that preserved traces of one of the earliest migrations of Homo erectus out of Africa. The site yielded hand axes and animal remains including a hippopotamus femur bone and a very-large pair of horns belonging to a species of extinct bovid – yet very few human remains. The site was discovered in 1959 and was first excavated between 1960 and 1974.

While they spanned from the Oldowan to the Middle Paleolithic Era, the purpose behind their creation has remained a subject of intense debate. Now, a study conducted by a team at HU’s Computational Archaeology Laboratory in collaboration with researchers from Tel-Hai Academic College (near Kibbutz Kfar Giladi and north of Kiryat Shmona) and Rovira i Virgili University in Spain’s Southern Catalonia has aimed at shedding light on these mysterious objects and offering insights into the intentions and skills of early hominins.

Spheroids are among the most lasting-yet-least-understood archaeological artifacts left over after being struck by another object. But the team’s research challenges this conventional wisdom. The central question at the heart of this study is whether these spheroids were unintentional by-products or intentionally crafted tools designed for specific purposes.

To answer this question, cutting-edge 3D analysis methods, including spherical harmonics and surface curvature, were applied to a collection of 150 limestone spheroids from the 'Ubeidiya archaeological site, dating back to about 1.4 million years ago. These methods were developed at the prehistoric archaeology lab directed by HU Prof. Leore Grosman. ‘Ubeidiya is presently recognized as the earliest known Acheulean occurrence outside of Africa, making it a crucial location for investigating the evolution of early hominin technology, she said.

How were the spheroids shaped?

The study entitled “The limestone spheroids of ‘Ubeidiya: intentional imposition of symmetric geometry by early hominins?” has been published in the journal Royal Society Open Science. 

The research team meticulously reconstructed the spheroid reduction sequence based on the trends observed in scar facets and geometry. Their findings revealed a remarkable pattern: the spheroids at 'Ubeidiya were crafted with a premeditated reduction strategy. Contrary to the notion that they were accidental by-products, the spheroids did not become smoother during their manufacture; instead, they became markedly more spherical. This transformation towards an ideal sphere required exceptional knapping skills and a clear preconceived goal.

Knappers use a soft hammer to shape a stone into many different kinds of cutting, scraping, and projectile tools. These techniques also create longer, thinner flakes, potentially allowing for material conservation or a lighter lithic (stone tool) kit to be carried by mobile societies.

This discovery challenges existing beliefs about the capabilities of early hominins and their relationship with technology, the team said. While Acheulean bifaces (flaked on both faces) are traditionally thought to represent the earliest evidence of hominins imposing intentional, symmetrical shapes on stone, the intentional production of sphere-like objects at ‘Ubeidiya similarly suggests that these early hominins had a desire for and achieved intentional geometry and symmetry in stone. Slightly older spheroids exist at sites in Africa, but if this same intentionality can be proven at the Jordan Rift Valley site, this would represent the oldest evidence of hominins desiring and achieving symmetrical shapes in stone.

The team said their research opens new avenues for understanding the cognitive abilities and technological achievements of our distant ancestors. It also raises questions about the purpose and significance of these spheroids in the daily lives of early hominins.