The Stone Age was also the Wood Age. But, until now, we haven’t seen it. Because if the lithic tools or shells used by prehistoric humans p through time without incident, the same is not true for objects made of organic matter, which require very specific conditions to avoid decomposition. It is therefore an exceptional discovery in more than one way that was announced on Wednesday September 20 in Nature, an international team: that of the oldest wooden structure ever unearthed. What’s more, it’s 476,000 years old, a remote era when modern humans had not yet appeared.
The find took place in northern Zambia, not far from the Kalambo River Falls. “The site is located on the edge of the river which causes regular flooding bringing sediment. It is thanks to this permanent humidity that the wood was able to be preserved”, specifies Veerle Rots, professor of prehistory at the University of Liège (Belgium) and co-signatory of the study. Excavated in the 1950s by the British archaeologist John Desmond Clark (1916-2002), this site “has already yielded interesting remains but which we did not know how to date: the chronological framework remained vague”adds Veerle Rots.
In 2019, a collaboration between the universities of Liverpool, Aberystwyth (United Kingdom) and Liège made it possible to relaunch excavations at Kalambo Falls. In the waterlogged sands, the team discovered several wooden objects, including an astonishing cruciform emblage. Two superimposed logs were embedded through a U-shaped notch, more than 10 centimeters wide, “clearly man-made”in the words of Veerle Rots, who bases his ertion on a series of marks left in the wood by stone tools.
A delicate point remained: determining the period in which this structure had been produced. Carbon-14 dating gave nothing because it does not 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 which act as electron traps. “Under the effect of natural radioactivity, these crystals accumulate energy and they release it when we heat them or when we light them in the laboratory”, explains Christelle Lahaye, professor of geochronology at Bordeaux-Montaigne University and director of the Archéosciences laboratory, which specializes in the study of archaeological heritage materials.
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