Water may appear to be the defining requirement for human settlement, especially in the Stone Age. Yet evidence from the Arabian Peninsula shows that an apparently green landscape with plentiful fresh water could still remain largely empty of human societies.

The peninsula was once lush and rich in water and animal life, but early humans seem to have left remarkably little evidence across parts of it. A new study examines why those inviting conditions did not lead to more widespread occupation.

An international group of researchers investigated the mystery by traveling into the Arabian Desert. Their work focused on a region whose modern conditions look dramatically different from the environment preserved in its ancient geological record.

Over 35 days in late 2023, the team drove about 1,500 kilometers, or 932 miles, across the Rub’ al Khali. The desert extends through parts of Saudi Arabia, Oman, the United Arab Emirates, and Yemen.

Today, the Rub’ al Khali is known as the “Empty Quarter.” The name reflects its lack of inhabitants, featureless sand dunes, and extremely arid climate.

The expedition nevertheless uncovered extensive signs that the region once supported a far wetter landscape. Researchers examined 125 localities along their route, and 55 contained clear evidence of ancient freshwater lakes.

That evidence included lake sediments, freshwater snail shells, and ostrich eggshells. Together, the findings showed that water and animal life had once been available in places now dominated by desert.

One important piece of the archaeological record was largely missing, however. Stone tools were scarce at the sites, suggesting that humans were not present or left very little evidence of their existence.

To investigate that absence, the researchers created a model reconstructing the ancient river systems and geology of the Arabian Peninsula. They then added the locations of 363 known sites made by ancient humans.

A clear pattern emerged from the combined information. Sites associated with early human occupation tended to cluster in regions that offered both water and stone suitable for making tools.

The type of stone mattered because early populations needed material that could be knapped into useful implements. A landscape could therefore contain fresh water and wildlife while still lacking another resource required for occupation and more complex culture.

Across the Arabian Peninsula, up to 57% of terrain rich in water sits on geological formations without knappable stone. That combination would have made many otherwise attractive locations very difficult for early humans to occupy.

The study’s findings suggest that water alone was not sufficient. Early humans needed access to both dependable water and workable stone if they were to settle and develop more complex cultures.

The researchers argue that this pattern was not limited to the Arabian Peninsula. Studies in Libya, Egypt, Tibet, South Africa, and North America also indicate that early humans often gathered near valuable stone sources rather than simply following abundant water.

The study authors warn that models of human movement can misjudge where populations were able to live if those models consider water but overlook geological resources. “Dispersal models that omit raw-material geology may systematically overestimate the habitable range of stone-tool-dependent populations,” they wrote.

Archaeological evidence is increasingly showing that the Arabian Peninsula did eventually provide a home for some human cultures. Those populations carved rock art and constructed vast monuments, although the source suggests that greater access to workable stone might have enabled even more human ingenuity.

The findings turn the ancient landscape into a lesson about the limits of apparent abundance. A place could be green, wet, and filled with animal life, yet remain difficult to inhabit when the geology offered little suitable material for essential tools.

The new study was published in the journal Nature. Its results place stone alongside water as a key factor for understanding where early humans could establish themselves and where even a lush environment might remain largely empty.