Boulders in Harcha Valley, Ethiopia
© H VEIT
Boulders were deposited by a glacier in the Harcha Valley, in Ethiopia’s Bale Mountains, during the last glacial period.
A rock shelter located in the hostile environment of southern Ethiopia's Bale Mountains has pushed back high-altitude living into the middle stone age.

The Fincha Habera site, 3500 metres above sea level, shows evidence of human occupation at least 31,000 years ago and as far back as 47,000 years ago, according to a new study published in the journal Science.

The Bale Mountains, like other high-altitude regions, including the Tibetan Plateau and the Chilean Andes, are unforgiving places. Oxygen levels are low, resources are scarce, and the climate can be cold and dry.

For a long time, this led scientists to believe that high altitude living - more than 2500 metres above sea level - is a relatively recent phenomenon. But discoveries in Tibet and elsewhere have been challenging this notion.

Stone tools on the Tibetan Plateau, for instance, were left by prehistoric people some 30,000-40,000 years ago, and the jaw of an ancient Denisovan hominin found in a cave on the edge of the Tibetan plateau is at least 160,000 years old.

The Fincha Habera site is noteworthy because objects found at the site indicate more than just a passing presence of early humans.

Animal remains, stone tools and fossilised poo - coprolites - suggest that whoever used the rock shelter did so for extended periods of time.

But it probably wasn't a permanent residence, according to archaeologist Götz Ossendorf from the University of Cologne in Germany, who led the excavations.

"They definitely were not continuously living there, because they were mobile hunter gatherers," he says. Instead, Fincha Habera "was probably one important site in the annual subsistence circuit".

Boulder in Ethiopia
© H VEIT
Sampling erratic boulders deposited by a glacier on the central Sanetti Plateau.
Artefacts found at the site, and in the surrounding areas, start to paint a picture of what life was like for people living there.

Giant mole rats from the region appear to have been a staple in their diet, and charred remains found at the site provide evidence they were cooked. But ostrich eggshells suggest they also gathered food from the nearby lowlands.

Meanwhile, the residents also ventured further uphill, to rocky outcrops located in an area that would have been at the edges of glaciers, which have long since melted.

Ossendorf and his colleagues used electron microprobe analysis to show that obsidian blades and scrapers found in the rock shelter were chemically identical to nearby obsidian outcrops at 4,200 meters above sea level.

"This tells us that people living at Fincha Habera definitely moved up to 4,200 meters and picked up or extracted the obsidian from there," says Ossendorf.

Fossil ground beetles near the rock shelter also suggest that the occupants would have had access to fresh water.

Radiocarbon dates for charcoal - a clear indicator of human presence - along with giant mole rat bones, coprolites and black carbon in the sediment point to a time of occupation between 31,000 and 47,000 years ago.

"It's a sound piece of work and that's what's important about a study like this when we start talking about first and earliest and highest," says archaeologist Mark Aldenderfer from the University of California, Merced, who wasn't involved in the study but wrote an accompanying commentary in Science.

"Clearly people are beginning to take seriously looking for these high-elevation sites and once we begin to find them, we're finding that they're earlier than we expected in many instances," he says.

"First" sites are really important, Aldenderfer adds. "It really makes a difference in how people then frame future research in those regions."

More sites with a range of artefacts present will help to fill out our knowledge of what people were doing at high altitudes and help pin down when people began to take up permanent residence in these harsh environments, he says.