Early humans appear to have avoided settling around ancient freshwater lakes in Arabia's Empty Quarter, and researchers now believe they did so because the lakes lacked suitable stone. Scientists who crossed the desert found that access to usable rock, not water alone, appears to have governed where prehistoric people lived.
The Rub' al-Khali, the Arabic name for the Empty Quarter, is the world's largest continuous expanse of wind-swept dunes, known as a sand sea. It covers about 650,000 square kilometres of the southern Arabian peninsula. Today the region is overwhelmingly dry, apart from a few permanent lakes in its interior fed by groundwater. Over the past century, however, scientists have uncovered evidence of numerous ancient lakes that formed during wetter periods, when stronger Indian Ocean monsoons helped transform parts of the peninsula into what researchers call Green Arabia.
Researchers have long suspected that these greener periods opened routes for early humans spreading out of Africa and across Arabia, an idea supported by stone tools found near ancient lakes. Yet nearly all such sites line the desert's margins, while the vast interior has remained largely unexplored. In 2023, Rudolf Dellmour of the University of Vienna and his team spent 35 days crossing the dunes and examined 125 locations for traces of ancient lakes, focusing on lakes present between roughly 122,000 and 67,000 years ago, when early humans were spreading into Arabia.
The team found evidence of ancient lakes at 55 of those locations. It included freshwater snail and clam shells, ostrich eggshell fragments and traces of animals that once burrowed into muddy lake beds. Despite these signs of a once-thriving environment, the researchers found no stone tools or other evidence that prehistoric humans had settled by any of the 55 lakes. « If we could spot a snail shell the size of a fingernail, we would have spotted a stone tool,» Dellmour said. « But there were none.»
To test whether the shortage of suitable stone could explain the absence of settlements, Dellmour, Jeffrey Rose of the University of Algarve in Portugal, and their colleagues turned to computer modelling. They mapped ancient water sources and the geology of the peninsula, then compared the results with the distribution of hundreds of archaeological sites recorded in earlier research. The analysis showed that 57 per cent of the terrain within reach of water lacked stone suitable for making tools, and that prehistoric settlements were concentrated where both resources were available.
Rose said the pattern reflects how stone-tool societies depended on their surroundings. « People who live by stone tools never stray far from good stone,» he said. « You just really don't see Stone Age sites unless you're within a few kilometres of an outcrop.» The researchers suggest that tool-making was relatively wasteful of raw material, meaning groups needed steady access to rock sources nearby. Because the study is based on the absence of evidence across a vast and difficult landscape, the team frames its conclusion as a strong working explanation rather than a final proof, and further fieldwork in the interior is needed to test it.
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