A 476,000-year-old wooden structure was discovered during archaeological excavations in 2019 near the Kalombo River in Zambia. LARRY BARHAM/UNIVERSITY OF LIVERPOOL
The Stone Age was also the Wood Age. But until now we haven’t seen it. Because if lithic tools or shells used by prehistoric people survive time without incident, this does not apply to objects made of organic matter, which require very specific conditions to avoid decomposition. It is therefore an extraordinary discovery in more ways than one that an international team announced on Wednesday September 20 in Nature: that of the oldest wooden structure ever excavated. Furthermore, it is 476,000 years old, a distant era in which modern humans had not yet emerged.
The discovery took place in northern Zambia, not far from the Kalambo River Falls. “The site is on the edge of the river, which results in regular flooding and sedimentation. Thanks to this permanent moisture, the wood was preserved,” explains Veerle Rots, professor of prehistory at the University of Liège (Belgium) and co-signatory of the study. This site, excavated in the 1950s by the British archaeologist John Desmond Clark (1916-2002), “has already produced interesting remains, but we did not know how to date them: the chronological framework remained vague,” adds Veerle Rots.
In 2019, a collaboration between the universities of Liverpool, Aberystwyth (UK) and Liège enabled excavations at Kalambo Falls to resume. In the flooded sand, the team discovered several wooden objects, including an amazing cross-shaped collection. Two tree trunks lying one above the other were embedded using a U-shaped notch more than 10 centimeters wide, “clearly man-made,” as Veerle Rots puts it, who bases his claim on a series of marks left in the wood by stone tools.
Luminescence dating
One delicate point remained: determining the period in which this building was built. Carbon-14 dating turned up nothing because it doesn’t allow us to go back further than fifty thousand years. To get their answer, the researchers used a technique that makes it possible to date not the object itself, but the sediments in which it is buried: luminescence dating.
This exploits the ability of certain natural crystals, such as quartz and feldspar, to behave like dosimeters thanks to small structural defects that act as electron traps. “Under the action of natural radioactivity, these crystals collect energy and release it when we heat them or when we light them in the laboratory,” explains Christelle Lahaye, professor of geochronology at the University of Bordeaux-Montaigne and director of the Archéosciences laboratory, that is specialized in the study of archaeological cultural heritage materials.
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