The Tsodilo Hills, “the rocks that whisper,” are a UNESCO World Heritage site. About 4,000 rock paintings have been created there over the past 100,000 years and more. To the indigenous people of the Kalahari, the “Bushmen” – also known as the “San” people – the hills are the cradle of humanity and are considered sacred lands. The area is like the Garden of Eden in San legends.

But how does that fit with the Kalahari itself, the “land without water,” where even the mighty Okavango River trickles away? Archaeologists have found the remains of fish in the Stone Age kitchen waste in the Tsodilo Hills. Did the fish come from the Okavango, 40 kilometers away?

Climate System Suspected to Differ from Previous Assumptions

Hartmann and Riedel have a different suspicion. They think that for a long time, there was a lake in the Tsodilo Hills that could have provided truly paradisiacal conditions. The interdisciplinary team of researchers is on the trail of a climate system in southern Africa that could have worked completely differently than had previously been assumed by a number of climate modelers. These modelers assume that the Kalahari was even drier millennia ago than it is today. A lake doesn’t fit this idea.

Hartmann (47) and Riedel (54) have found an outdoor lab they can use to test their hypotheses regarding the climate system of southern Africa. Their goal is to reconstruct the history of the lake, and with it, the Stone Age environment. Their research is being supported by the German Research Foundation (DFG).

Close Cooperation with African Researchers

The researchers from Berlin and their two students, Venise Bayer and Robert Wiese, are not entering the Kalahari as academic colonialists. Instead, they are working closely with colleagues from Botswana International University of Science and Technology (BIUST). The Botswanan colleagues are using geophysical methods to scan the soil below the erstwhile lake to find out how thick and extensive the deposits are. Hartmann is using mathematical modeling to connect the subsurface with the surface. Geomorphological studies of the site and remote sensing data show that the body of water occupied about 30 square kilometers.

Fresh or Salt Water?

But what kind of lake was it? Was the water potable? Were there resources that the Stone Age people could use as sources of food? Or did life-threatening parasites pose a risk to the people in the area? How did the lake affect the local vegetation? This is where Riedel comes in. He is studying the ecology of the prehistoric lake based on fossils. He can use ostracod shells, diatom skeletons and snail shells to reconstruct the lake’s salt content, temperature, mixing, pH level and nutrient content.

“Right now everything is tending to point more toward a freshwater lake,” Riedel says. A method developed at Freie Universität Berlin makes it possible to identify precipitation signals using the isotope relationships in the fossilized shells of aquatic snails. The goal of doing this is to find out, for example, whether there were more pronounced periods of rain in the distant past than there are today.

The rainy season was practically nonexistent last year. Riedel and Hartmann noticed this from a number of indicators, including the fact that a strikingly large number of elephants left drought-stricken areas and moved toward the Okavango. At one point, the team needed to get gasoline for the generator from the nearest larger town, but work had to be suspended for a day because a herd of elephants was blocking the road.

A Good Working Relationship with the San Chief

“You have to go into the field and study the actual processes in order to reconstruct the past,” Hartmann points out. “And without personal ties with the village chief and the management of the UNESCO World Heritage site, that doesn’t work at all. Sometimes you even have to spend half a day chatting, but the responses are always great.”

Riedel, who is two meters (over 6’ 6”) tall, enthuses over the San chief, who is two heads shorter. “He’s a very heartfelt guy. He hugs us as a greeting,” Riedel says. The San chief earns his living as a guide for tourists in the Tsodilo Hills. His brothers and sons helped out with the excavation work in exchange for reasonable pay. Using pickaxes and shovels, the team opened up large areas of ground extending over several meters, digging into the rock-hard lake sediments. The scholars used hammers, chisels, and angle grinders to take samples in five-centimeter intervals. Each sample is a repository of the lake’s history, and 120 kilograms of sediment samples were sent to Berlin for analysis.

Discovering Botswanan Heritage Together

The project is running according to plan, and Riedel and Hartmann assume that they will be able to submit an application for continued funding to the DFG in the spring of 2016. Alongside the scientific and scholarly challenge, they are also driven by the fact that the people of Botswana appreciate learning more about their cultural heritage. A find containing fossils from the prehistoric lake is now on display at the UNESCO World Heritage Museum in the Tsodilo Hills.