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Between approximately 112,000 and 121,000 years agoa handful of people were walking along the muddy banks of a lake in what is now the Nefud Desert in Saudi Arabia. Elephants and camels had stirred up the ground and humans left seven footprints among hundreds of animal tracks before the sediment sealed the entire scene for eternity. When researchers describes the sitecalled Alathar (Arabic for “the trace”), in a 2020 article in Scientific advances, we called the footprints “the oldest human footprints ever found on the Arabian Peninsula” and was surprised that they had survived. As the researchers noted, an experimental study of modern footprints in mudflats “found that the finest details were lost within two days and the prints became unrecognizable within four days.”
Six years later, the original interpretation still stands. “The age estimate is about 120,000 years old, based on scientific dating,” said Michael Petraglia, a researcher. archaeologist at Griffith University in Australia who studies human evolution and dispersal, tells Popular mechanics. “The size and shape of the prints conform to Homo sapiens“What has changed is the record surrounding them. Petraglia says the sites dated 2020 suggest that people entered Arabia when wetter weather filled the peninsula with lakes. During these periods of “Green Arabia”, people could find drinking water in places that are now deserts. When the water disappeared, some of these populations may have disappeared with it, perhaps including the people who left Alathar’s tracks.
The desert kept opening and closing
Arabia has gone through this cycle several times. For a Study 2021 In NatureHuw Groucutt, Petraglia and their colleagues dated ancient lake deposits in Nefud that contained stone tools and animal fossils. They found that human ancestors moved into the Arabian interior at least five times between 400,000 and 55,000 years ago, each time during a wetter period, and that each phase had its own style of stone tools. “It appears that different populations, even species, move through the area at different times,” explains Grucuttarchaeologist and lecturer at the University of Malta who studies human prehistory and environmental change. Once the rains stopped, he said, there probably wasn’t enough water for anyone to stay.
Even in good years, people probably continued to move. Groucutt depicts groups traveling among small, scattered lakes and other water sources in a landscape that is still very seasonal, with very hot summers. Alathar fits this image. The researchers discovered no stone tools or dismembered bones at the site and concluded that the lake “was only briefly visited by people”, probably for drinking water. For Petraglia, this brevity is what makes the leads valuable. “The footprints capture a moment in time, illustrating that people walked along the shores of the lakes at the same time as the animals,” he says.
These walkers may not have living descendants
If Alathar’s walkers were Homo sapiens, Groucutt believes they belonged to a branch of humanity that did not survive. “The prevailing view in genetics is that people living outside of Africa today are descended from people who spread into Asia about 50 to 80,000 years ago, so the earlier peoples died out,” he says. According to this reasoning, the footprints are “probably an example of an earlier migration that failed.” This type of migration failure is also known from other sites, including Skhul Cave on Mount Carmel, where fossils of early Homo sapiens were found. Reaching Arabia therefore carried no guarantee of survival there. The people who left these traces may have disappeared, and a much later migration brought the ancestors of most people living today outside of Africa. Petraglia describes the same pattern of changing fortunes: “The migrations were repeated movements, with groups expanding, contracting, and perhaps disappearing from parts of the peninsula as conditions changed. »
Maybe the green windows were traps
As Arabia dried out, Groucutt thinks, people may have retreated south, following the water to the wetter parts of the peninsula. The differences in stone tools suggest that these southern populations developed their own ways of doing things as they lost contact with people further north. But the south eventually dried up too. Groucutt interprets gaps in the archaeological record as a sign that remaining groups became too small and isolated to survive the worst periods of drought. The same lakes that drew people to Arabia could leave them stranded, crowded around the remaining water and with fewer and fewer places to go. Alathar’s tracks date from a period of drought during the last interglacial, placing their creators in exactly this kind of shrinking landscape.
Proof is hard to find in a hot desert
To resolve the question, it will be necessary to prove that a desert does not give up easily. Groucutt would welcome hominid fossils, although he doubts they are the “smoking gun” that people sometimes imagine, because bones can be difficult to date and assign to a species. Ancient DNA could do more, but in low latitudes, “it doesn’t go back that far,” he says, because “hot places are bad for storagePetraglia is looking for something more specific. “A well-dated human fossil or a long layered sequence showing human occupations during wet and dry periods would be transformative,” he says. Working with Saudi colleagues who help choose sites and reach them, his team searches around ancient water sources for evidence of people who stayed as the climate changed.
Until this evidence is discovered, Alathar’s footprints remain one of the few direct traces of these early travelers. If they left no descendants, the name of the site perhaps best describes what remains of them: a trace.
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