Access to fresh water is often treated as a key factor in where early human groups settled. But a study published in Nature suggests that, in prehistoric Arabia, water was not enough: people also needed suitable stone to make tools. That may explain why archaeological remains are concentrated around the desert’s margins, even though some inland areas also had water sources.
During periods of favourable climate, monsoon rains created lakes and grazing land in areas now covered by dunes. Yet the oldest human traces are generally found near the desert’s edges. To investigate why people did not also settle in the water-rich interior, a team led by Jeffrey I. Rose of the University of Algarve carried out a field expedition of around 1,500 kilometres.
The researchers surveyed 125 locations, examining dry lake sediments, soil minerals and exposed surfaces for stone tools and other material evidence. They found indications of ancient lakes at 55 sites, along with fossil shells and fragments of ostrich eggshell. The survey did not identify evidence of early human occupation at the 125 locations.
Comparing their geological mapping and reconstructions of ancient river courses with 362 previously catalogued prehistoric sites, the team estimated that 57% of areas with easy access to water lacked suitable rocks for toolmaking. The findings suggest that inland valleys could have offered water but not the raw material people needed for everyday tools.
The researchers conclude that water and workable stone had to be available together for a settlement to last. They also warn that models of ancient human movement based mainly on water sources may overestimate how much land was habitable, because they can overlook the geological resources required by communities that relied on stone tools.
Sources: elDiario.es.