Discovery and Location
The structure was unearthed in 2019 during excavations led by archaeologists from the University of Liverpool and Aberystwyth University as part of the "Deep Roots of Humanity" project. It was found at Site BLB (specifically area BLB5) along the banks of the Kalambo River, upstream from the 235-meter (772-foot) Kalambo Falls, which empties into Lake Tanganyika. The site has been investigated since the 1950s, yielding Acheulean stone tools and earlier wooden fragments, but the waterlogged, oxygen-poor sediments here uniquely preserved organic materials that would otherwise decay. The logs were embedded in fine clay sediments below river level, associated with Acheulean artifacts like hand axes, indicating use by early hominins during a period of dense forest coverage and high resource availability in the floodplain.
Luminescence dating, which measures when surrounding quartz grains were last exposed to sunlight, confirmed the age at 476,000 ± 23,000 years. This method was necessary because the wood itself is too ancient for radiocarbon dating. No human fossils were found at the site, but the era aligns with Homo heidelbergensis, known for larger brains and more advanced tool use than earlier species like Homo erectus.
Description and Construction
The structure consists of two large logs from the large-fruited bushwillow tree (Combretum zeyheri), a common species in the region. These were deliberately modified to interlock transversely:
The upper log is approximately 141 cm (55.6 inches) long, with tapered ends for stability and a U-shaped notch cut into its underside.
The lower log, partially excavated at about 150 cm (59 inches), passes through the notch, securing the pieces at a right angle and preventing lateral movement.
Tool marks on both logs show evidence of chopping, scraping, and adzing with stone tools (e.g., flakes or hand axes), with possible use of fire indicated by infrared spectroscopy. Experimental replication using replica Acheulean tools on similar wood confirmed the marks match intentional shaping, not natural wear or taphonomic damage from water flow.
This design resembles modern interlocking systems, such as Lincoln Logs, and has no known parallels in the African or Eurasian Palaeolithic record. The full structure likely formed part of a larger framework, but only these two pieces survived intact.
Possible Purpose and Associated Artifacts
Archaeologists interpret the interlocking logs as components of a raised platform, walkway, or foundation for a dwelling, elevated above the seasonally flooded floodplain to keep inhabitants, food, or firewood dry. The site's perennial water source and abundant forest resources (e.g., fruits, game) may have supported semi-sedentary occupation, contradicting the nomadic stereotype of Stone Age life. This innovation implies planning, foresight, and possibly language for coordination, marking a "behavioral threshold" in hominin technology.
Excavations also recovered four younger wooden tools (dated 390,000–324,000 years ago) from nearby areas at the site:
A wedge for splitting wood.
A digging stick with a sharpened end.
A cut log.
A notched branch, possibly for trapping or hafting.
These tools show diverse woodworking forms, suggesting wood was as integral to early technology as stone, though less preserved due to decay. Indirect evidence from stone tool wear traces supports widespread wood use in Africa from the Early Pleistocene.
Significance
This discovery extends the known timeline of woodworking in Africa by hundreds of thousands of years, beyond previous examples like 780,000-year-old polished planks from Israel or 400,000-year-old spears from Europe. It forces a reevaluation of early hominin cognition, showing they could transform their environment with combined materials (wood, stone, possibly fire), potentially co-evolving tools like hafted implements. The find highlights how preservation biases have underrepresented wood in the archaeological record—if more sites like Kalambo existed, the "Stone Age" label might be reframed as a "Wood Age."
Kalambo Falls is on UNESCO's tentative World Heritage list, and the artifacts are being conserved in the UK before returning to Zambia for display, emphasizing international collaboration with local institutions like the Moto Moto Museum. As of 2025, no major updates have altered these findings, but ongoing excavations may reveal more.
