Ancient Wooden Structure Unearthed at Zambezi Kalambo Falls Reveals Early Human Ingenuity

The Zambezi Kalambo Falls, one of the world's twelve largest waterfalls, is not only a tourist attraction but also a sacred site for archaeology where primitive tools have been unearthed.

However, archaeologists working here always have to race against time. Once the seasonal floods strike, the excavation site will cease to exist, and various artifacts will be washed away.

However, the flood season of 2019 brought not destruction, but new discoveries for archaeologists. Lawrence Barham, an archaeologist from the University of Liverpool, and Geoff Duller, a geochronologist from Aber University, discovered a protruding "stick" with engravings on the sandy beach of the Kalambo River under a small cliff.

"That was a truly crazy moment," Barham recalled. The wash of the river took away the sand, revealing the stick.

Following this stick, they unearthed part of the structure of an ancient wooden building deep in the riverbank. Using optically stimulated luminescence dating techniques, the researchers determined that the building was constructed by our human ancestors about 476,000 years ago.

In their recent article published in Nature, they pointed out that the excavated wooden structure consisted of a pair of carved logs, which were connected together through carved notches. This might be the earliest known wooden structure, significantly predating the emergence of modern humans.

Andy Herries, a paleoanthropologist and geoarchaeologist from La Trobe University in Australia, said that wooden artifacts are relatively rare because wood decomposes faster than stone.

However, there are some ancient wooden artifacts preserved in the world. For example, a wooden spear discovered in Germany dates back 300,000 years, and a polished wooden board fragment from Israel is believed to be 780,000 years old.

Barham stated that although the humid environment near Kalambo Falls is not friendly to excavation work, it is an ideal environment for preserving wood because the sediment in the water can prevent wood decomposition. Over time, the wood also absorbs minerals dissolved in the water, making it stronger.

The one-meter-long log discovered by Barham and Duller has obvious engravings on its surface, which are likely to have been intentionally carved out by ancient humans using stone tools. These notches and the interlocking design suggest that these wooden structures might have been part of a walkway, or possibly the foundation of a bridge or a dwelling. This suggests that ancient humans did not all live a nomadic life; some were also building fixed settlements.

The research team used optically stimulated luminescence dating for age determination of the wood. Some sediments contain minerals that can absorb environmental radioactivity and store it as energy. When scientists release this stored energy in the laboratory, these minerals emit a faint light. The intensity of this light is an indicator of the last time the sediment was exposed to sunlight.

The mineral usually used for optically stimulated luminescence dating is quartz, but in this study, Barham and his team chose feldspar because it can absorb more radioactivity than quartz. Feldspar particles in the sediment wrapping the logs suggest that these logs are about 476,000 years old.

Researchers suggest that while early humans are commonly thought to have lived in caves or led a nomadic life, the new study shows that our ancestors were capable of constructing independent structures and shaping their environment to meet their needs.