In the heart of the world's largest sand desert — the Rub' al Khali — there once existed freshwater lakes surrounded by life, yet traces of humans there were almost absent. An expedition stretching about one and a half thousand kilometers revealed deposits of ancient lakes at 55 of 125 surveyed points, but not a single stone tool or suitable raw material for making them in the depths of the desert.
A study published in the journal Nature shows that access to water was necessary but not sufficient. The geology of the region explains the paradox: rocks yielding flint, quartz and other materials suitable for knapping into sharp tools outcrop only along the edges of the desert. In the center they are hidden beneath a thick layer of sand and salt flats, while the lakes were fed mainly by groundwater that did not bring stone from afar.
Scientists from the University of Vienna, the University of Algarve and other institutions compared the expedition's data with the distribution of 363 known Middle Paleolithic sites on the Arabian Peninsula. A computer model accounting only for proximity to water predicted the location of sites with an accuracy corresponding to an area under the ROC curve of 0,695. Adding the factor of the presence of suitable stone raised this indicator to 0,768.
At the same time, 57 percent of the territories within reach of water lie on geological formations without raw material for tools. Settlements were concentrated precisely where both resources coincided. A similar pattern can be traced in other regions as well — from the Messak Plateau in Libya to the Eastern Desert of Egypt and Tibet.
For Stone Age people, tools were not merely instruments but a condition of survival in an unfamiliar environment. Without the ability to quickly make a knife or a scraper, even a place rich in water became a dead end. The model shows that previous reconstructions of dispersal routes out of Africa, which relied predominantly on climate and water, may have substantially overestimated the areas suitable for long-term habitation.
The discovery underscores how closely resources were intertwined in the life of ancient communities: water gave life, stone gave the ability to sustain it. Similar constraints probably influenced both the speed and the directions of migrations into other arid zones of the planet.
The study reminds us that to understand the past it is important to consider not only obvious factors such as water, but also those that provide the technological basis of existence.
