An international team of researchers has found evidence that hot springs existed in Olduvai Gorge — a paleoanthropological site in the Great Rift Valley in Tanzania that has yielded some of the most significant fossils of hominins, such as Paranthropus boisei, Homo habilis and Homo erectus — around 1.7 million years ago. These hydrothermal features may have provided a convenient way to cook food, for instance to boil fresh kills or certain tough tubers and roots, that would have required minimal effort.
The proximity of hot springs to early settlements have led Sistiaga et al to wonder if early humans used hot springs as a cooking resource long before fire. Image credit: Tom Björklund.
MIT’s Professor Roger Summons and his colleagues from the United States, Spain and Talzania collected and analyzed sediments from a 3-km-long layer of exposed rock that was deposited in Olduvai Gorge around 1.7 million years ago.
The researchers looked for signs of certain lipids that can contain residue of leaf waxes, offering clues to the kind of vegetation present at the time.
“Something was changing in the environment, so we wanted to understand what happened and how that impacted humans,” they said.
“It’s thought that around 1.7 million years ago, East Africa underwent a gradual aridification, moving from a wetter, tree-populated climate to dryer, grassier terrain.”
Within the sediments they brought back, they came across lipids that looked completely different from plant-derived lipids.
They realized that the lipids were a close match with lipids produced not by plants, but by modern bacteria they previously studied in the United States, in the hot springs of Yellowstone National Park.
One specific species of bacterium, Thermocrinis ruber, is a hyperthermophilic organism that will only thrive in very hot waters, such as those found in the outflow channels of boiling hot springs.
“They won’t even grow unless the temperature is above 80 degrees Celsius (176 degrees Fahrenheit),” Professor Summons said.
“Some of the samples from this sandy layer in Olduvai Gorge had these same assemblages of bacterial lipids that we think are unambiguously indicative of high-temperature water.”
That is, it appears that heat-loving bacteria may also have lived in Olduvai Gorge 1.7 million years ago.
By extension, the team proposes, high-temperature features such as hot springs and hydrothermal waters could also have been present.
“It’s not a crazy idea that, with all this tectonic activity in the middle of the rift system, there could have been extrusion of hydrothermal fluids,” said Dr. Ainara Sistiaga, a researcher at MIT and the University of Copenhagen.
“Olduvai Gorge is a geologically active tectonic region that has upheaved volcanoes over millions of years — activity that could also have boiled up groundwater to form hot springs at the surface.”
While there is currently no sure-fire way to establish whether early humans indeed used hot springs to cook, the scientists plan to look for similar lipids, and signs of hydrothermal reservoirs, in other layers and locations throughout Olduvai Gorge, as well as near other sites in the world where human settlements have been found.
“We can prove in other sites that maybe hot springs were present, but we would still lack evidence of how humans interacted with them,” Dr. Sistiaga said.
“That’s a question of behavior, and understanding the behavior of extinct species almost 2 million years ago is very difficult.”
“I hope we can find other evidence that supports at least the presence of this resource in other important sites for human evolution.”
The study was published in the Proceedings of the National Academy of Sciences.
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Ainara Sistiaga et al. Microbial biomarkers reveal a hydrothermally active landscape at Olduvai Gorge at the dawn of the Acheulean, 1.7 Ma. PNAS, published online September 15, 2020; doi: 10.1073/pnas.2004532117
