Early humans crossed the world’s largest sand sea with plenty of fresh water around, yet they left nothing behind.
The team drove about 1,500 kilometers through the Rub’ al Khali, the huge desert in southern Arabia, in late 2023.
They found no stone suitable for making tools either, apart from small amounts at 10 spots near the desert edges.
Of the land near water, 57 percent sits on rock with no knappable stone.
In Libya’s Messak Plateau, 91 percent of Middle Stone Age finds sit near one rock outcrop, despite water across nearby lowlands.
Early humans crossed the world’s largest sand sea with plenty of fresh water around, yet they left nothing behind. A team led by researchers at the University of Vienna and the University of the Algarve now says the missing ingredient was stone.
The team drove about 1,500 kilometers through the Rub’ al Khali, the huge desert in southern Arabia, in late 2023. Eight people in three vehicles spent 35 days checking 125 spots. Between roughly 122,000 and 67,000 years ago, monsoon rains filled this basin with lakes. The crew found lake deposits at 55 spots, along with freshwater snail shells and ostrich eggshell fragments.
They found no tools, though. They found no stone suitable for making tools either, apart from small amounts at 10 spots near the desert edges. Ground visibility topped 95 percent, so any chipped stone would have stood out. Even those 10 spots with raw material held no artifacts.
People did live around the edges of the desert at the same time. Sites at Mundafan, Jebel Faya, Umm al Sha’al and the Dhofar Nejd plateau all date to this period. Those groups made tools from local stone. The desert’s interior surface is made only of carbonate and evaporite rock, which doesn’t break into sharp edges. The old lakes were fed by groundwater, so no rivers carried useful stone in from far away. Around 800 kilometers of basin had none.
Next, the researchers built a computer model for the whole Arabian Peninsula. It combined distance to water with the presence of rock that can be flaked. They tested it against 363 known Middle Paleolithic and Middle Stone Age sites. Sites clustered in zones where both resources overlapped. Water alone predicted site locations with a score of 0.695 on a standard accuracy scale. Adding stone raised it to 0.768. Of the land near water, 57 percent sits on rock with no knappable stone.
The authors point to similar patterns elsewhere. In Libya’s Messak Plateau, 91 percent of Middle Stone Age finds sit near one rock outcrop, despite water across nearby lowlands. Egypt’s Eastern Desert and Tibet show the same tie to stone sources. Central Oman gives the reverse case, with abundant chert but little water and very few sites.
Why couldn’t people just carry stone in? Past studies show most tool material comes from within about 5 kilometers, and sources beyond 20 to 30 kilometers usually supply only 1 to 2 percent. The nearest stone lay more than 200 kilometers from the surveyed lakes. Carried pieces might supply a visit, but not daily tool making for a resident group over generations. The same absence shows up in the Early Holocene, when the basin refilled with water again and still yielded no cultural material.
The authors call the “Green Arabia” of wet periods a lithic archipelago, with islands set by geology as much as by climate. They say dispersal models built on water and climate alone probably overstate how much land stone-tool users could settle. The team notes its limits. The geology maps have a coarse scale, shells were identified from photos, and future work could still find small short-term camps in the interior.
