A new study has expanded the range of liveable regions in modern-day South africa’s interior for our human ancestors 200,000 years ago
Lining the Cape of South Africa and its southern coast are long chains of caves that nearly 200,000 years ago were surrounded by a lush landscape and plentiful food.
During a glacial phase that lasted between 195,000 to 123,000 years ago, these caves served as a refuge to a group of humans that some researchers think were the only people to survive this ice age, called Marine Isotope Stage Six, or MIS6. And in this coastal region, a lot of archaeological research has taken place.
Of less interest to archaeologists has been the interior of South Africa, which was thought to be an uninhabited, inhospitable place during at least two waves of ice ages, MIS3 and 2.
Now, a study has shown that the region might have been more fertile and temperate during these two glacial periods than previously thought and that the region likely played host to human populations living around a series of paleolakes.
The study, led by University of Michigan archaeologist Brian Stewart, provides a more comprehensive timeline of the age and stages of these lakes, and shows human fingerprints across the region.
Stewart said: “There’s this perennial assumption that human population centres were always along the coast and that the interior, especially the southern interior of the Karoo Desert, were largely depopulated for long stretches of time.
“The funny thing is that one just has to go into the interior and walk around and notice that there’s archaeology everywhere.”
But to flag the region as worthy of archaeological attention, the researchers needed to show that humans could have actually lived there.
The research team, an international group including researchers from South Africa, the United Kingdom and France, examined a series of super flat areas of land ringed by higher ground.
They showed that these regions, called ‘pans’ in Afrikaans, are ancient lake beds, while the areas of higher elevation that encircle them are erosional landforms and sedimentary deposits left over from their ancient shorelines.
This suggests that these time periods were not as dry in this region as previously thought; there would have needed to have been sustained rainfall and humidity to keep these lakes full.
The more temperate climate required to sustain lakes also meant the landscape was also able to sustain both vegetation and animals required to support human populations.
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Reconstructing the paleolakes
The researchers used a variety of technologies to date and reconstruct these ancient lakes, shorelines and lake bottom deposits, and to recreate the landscape of the region.
These include radiocarbon dating and a technique called luminescence, which measures the radioactivity of tiny crystals of quartz or feldspar that haven’t seen the light of day since they were covered by sediment tens of thousands of years earlier.
While buried, electrons from radioactive elements common to all sediments get trapped in these crystal matrices at a constant rate.
By measuring how many electrons accumulated in the sample and comparing that to the degree of background radioactivity, the researchers can predict its age.
The researchers used these techniques to date columns of sedimentary lakeshore and lake bottom deposits, called lacustrine deposits, found surrounding and within a series of three pans dotted across a region some 100,000 square miles, about the size of Texas.
They also aged the shells of freshwater molluscs found scattered throughout the region and embedded within the sedimentary lake deposits.
An aquatic gastropod, Tomichia ventricosa, found at a pan called Swartkolkvloer, was embedded in a column of lacustrine deposits. Together, the deposits and shells were radiocarbon dated to two time periods: approximately 39,000 to 55,000 years before present; and approximately 31,000 to 34,000 years before present.
At another pan called Grootvloer, the researchers found a freshwater mollusc called Unio caffer, which required ‘perennial freshwater’ and the presence of fish to reproduce.
These shells and lacustrine deposits in this pan were dated to between approximately 20,000 to 22,000 years before present.
The researchers were also able to predict the area of land the lakes encompassed, as well as how deep they were, based on the height of the lacustrine deposits ringing their shorelines.
For example, they determined that the paleolake at Swartkolkvloer was about 83 miles square and 59 feet deep, while the paleolake at Grootvloer was likely about 17 miles square and 62 feet deep.
Another pan called Alexanderfontein, some 300 miles northeast near the town of Kimberley, held a lake about 13.5 miles square and 48 feet deep.
Based on these parameters, the researchers knew the lakes would have required a climate drastically different from the one that exists in South Africa’s interior today.
Stewart said: “In various parts of the interior, between about 60,000 to about 12,000 years ago, we can see that there were enduring phases of pretty large bodies of water kicking around what used to be thought of as an arid and inhospitable environment.
“This was a period that used to be thought of as notoriously dry and freezing cold in the winter. But we’ve got this evidence for these large lakes existing during this time period.”
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Scattered alongside the lakes are human artefacts such as triangular points, bladelets, weathered ostrich shells and other assemblages.
Much of these are from the Middle Stone Age, which ranged from about 280,000 years ago to about 25,000 years ago, and the Later Stone Age, which lasted from 25,000 years ago right up to European contact in the 15th Century.
Stewart said: “There’s Middle Stone Age archaeology just everywhere. You can’t drive anywhere and open the car door and not step on it. It’s astounding how much there is.”
He said their findings could also expand the region where archaeologists think humans became more behaviourally complex.
Over the past decades, researchers have found evidence that humans living in coastal South Africa started making the leap into complex thought, showing some of the earliest signs of behavioural complexity.
It was thought that both climate and nutrient stability – including the rich omega fatty acids gleaned from seafood – allowed humans here to become behaviourally modern.
The group’s work may challenge this idea by suggesting that favourable conditions for hunter-gatherers were not confined to the coastline but probably characterised many regions as climates changed, including the interior, current-day desert.
The research is published in PNAS.
Image: South Africa’s arid interior was not always so uninviting. Copyright: M Thame.