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Desert regions in and the have been well studied by archaeologists as the and as routes of along 鈥溾��. The archaeology of southern Africa鈥檚 west coast desert belt has not received the same attention.
The Namib Sand Sea, part of the Namib Desert, is on the west coast of Namibia. It is a hyperarid landscape of towering dunes, occupying about 34,000km虏 between the towns of L眉deritz in the south and Walvis Bay in the north. However, there are clues that this environment was not always so dry and inhospitable, suggesting that there is more to be learnt about ancient human life here.
We are part of an interdisciplinary research team of physical geographers, archaeologists and geospatial scientists, interested in the long-term history of deserts and human-environmental interactions.
Our provides a timeframe for the presence of a small freshwater lake that once existed in the Namib Sand Sea. This lake was fed by an ancient river and is surrounded by a rich record of stone tools from the (made between about 300,000 years ago and 20,000 years ago), indicating that people ventured into this landscape and used this occasional water source.
Dating the former lake site, Narabeb, makes it clearer when ancient humans would have been able to live here. It draws attention to the Namib Sand Sea as a place archaeologists should study to learn more about far-reaching and deep human connections across southern Africa.
An ancient lake and shifting sand dunes
Today, Narabeb is a landscape dominated by long sand dunes that tower more than 100 metres high over the former lake site. There is no standing water here and the landscape receives little to no rain most years. However, that鈥檚 probably not what our ancient ancestors would have seen here. Away from the lake, they might have seen a relatively flat plain, seasonally covered by grasses, beside a river.
The clue is in sediments at the site: mud layers that were laid down by water. To find out how long ago the lake was at Narabeb, we needed to date these layers.
We used a technique called 鈥� basically, making sand glow to tell the time. Sand grains release a trapped signal that builds up when sand is buried underground, and is reset when sand is exposed to sunlight. Using this technique, we can date when different layers were last on the surface before they got buried. We dated the sand beneath and above layers of mud that were deposited by water. Our results show that the lake was present at Narabeb at some point between 231,000 卤 20,000 and 223,000 卤 19,000 years ago and again about 135,000 卤 11,000 years ago.
Another clue is the shape of the landscape east of Narabeb. It is dune free, reminding us that ancient humans were not the only things migrating in the Namib Sand Sea. Have the dunes been on the move? For how long? And how quickly?
Drilling to the centre of these dunes to work that out remains logistically impossible. Instead, we used .
The modelling suggests that it would have taken around 210,000 years to accumulate the amount of sand around Narabeb (those 110m high dunes). This number is remarkably close to the oldest age for the lake. This suggests that the dunes may only just have been starting to form and that a river was supplying the lake with fresh water, supporting animals and attracting people. The sediments at Narabeb also clearly tell us that a river once flowed where there are now dunes.
The winds have pushed dunes from the south and west to north and east, creating barriers for the river and hindering movement of people and animals along the water course.
Ancient human presence
At we have found tools from an earlier species of the Homo genus. This is part of a growing body of evidence, adding to research in the Kalahari desert in the centre of southern Africa, that suggests to the story of human evolution and technological innovation than has been supposed.
The artefacts from Narabeb fit into the Middle Stone Age type of stone tool technology. Narabeb is a particularly rich site for stone tools, suggesting people made tools here for a long time and perhaps visited the site over many generations.
This research illustrates the need for a comprehensive study of areas that have not been on the map of the major routes of human and animal migration. These might reveal exciting records of diffusion, innovation and adaptation to marginal and changing environments.
Our results also make us think about the dynamic nature of environmental conditions in one of Earth鈥檚 oldest desert regions. It has long been thought that the Namib has been consistently very and not a place capable of containing 鈥済reen corridors鈥� at the times of interest for archaeologists. Now we can challenge that idea.
Future steps
Recent funding from the will allow us to extend our fieldwork, documenting archaeological sites and dating these 鈥済reen corridors鈥� across more of this landscape. along the ancient river course has revealed an expansive artefact-littered landscape. We also need to know more about where ancient populations found the materials they used to make stone tools.
This will allow us to piece together a network of archaeological sites and show where human migration might have been possible in this part of southern Africa. Up to now, it鈥檚 been a gap in the archaeological map.
More work is also needed to understand the shifts in climate that allowed the rivers to flow into the Namib. This Southern Hemisphere, west coast desert has a very different setting to north Africa and Arabia, which have for understanding their periodic 鈥済reen corridors鈥�. Ongoing work with the wider scientific community, including climate modellers, may create a clearer picture of the Namib鈥檚 鈥済reen corridors鈥�.
, Reader in Physical Geography, and , Professor of Archaeology,
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