When the Sahara was green (II)The Sahara has not been always the most impressive desert in the world. Instead of this kingdom of rocks and sand, desolated and arid, existed in remote times a verdant and populated region. This is the testimony of the civilizations that flourished on the Central Sahara, civilizations that were extinguished when the wind of the desert covered the greenery with a shroud of sand.
Morphology of the SaharaNothing is easy in the Sahara, but however, a wide variety of animals survive there, fighting against the heat and the drought. Some species, such as rodents, carnivores or reptiles, pass the most part of the time in their lairs, getting out only during the cooler hours, and specially during night time. Camels and antelopes, who can accumulate water in their stomaches, were able to endure the new climatic conditions and for that reason they are habitual inhabitants of the Sahara. In the mountain basins feed by perennial springs have survived fish and amphibians. Fish can be evicted from the perennial basins during the violent overflows, being trapped in temporal lagoons, that after being evaporated leave uncovered thousands of dead fish. Plants defend themselves by multiplying their roots to better catch the humidity on the subsoil, and the seeds can wait during years within the pebbles the arrival of the next rainfall that will give life to them, covering the stony fields with a mantle of colorful flowers. In the highlands of the Air, Ahaggar or Tassili-n-Ajjer survive ancient cypresses and olive trees, possibly thousands of years old. When they were born, the slopes of the mountains were covered with them; today, unable to reproduce themselves, defy the pass of the time.
The olive tree is a vestige of the mediterranean flora that covered the massifs of the Central Sahara during the Neolithic. Certain exemplars could have thousands of years.
Climatically the Sahara belongs to the continental system. Because of its location in the Tropic of Cancer, it is subject to season regime in which heat and cold alternate with transition stages. During winter and in the highlands the temperature can drop to -10º C or even more. Sometimes it snows in the Ahaggar or in Tassili-n-Ajjer, albeit the snowflakes barely remain more than a couple of days. During summer, the temperature reaches up to 54º C on the shadow. Nights are generally cold. This provokes, specially during summer, phenomenons of expansion and contraction in the rocks, to the point that some nights one can hear the moaning sounds of the rocks, along with the fall of detached stones. Masses of sand, annexed to the great dunes, because of the successive expansion and contraction of the sand grains, are detached from the main mass and slide producing a deaf and prolonged bellow.
In the beginning of the 20th century, the geologist Fernand Foureau would earn fame for crossing the Great Eastern Erg and ultimately for his great transaharan expedition from Ouargla to Chad; he was the first investigator that paid attention to the stone tools and collected them, encouraging further prehistoric investigations on the Sahara. From 1933 onwards, the first bony vestiges from the Paleolithic were found, belonging to archaic elephants, hippopotamus, buffalos and bovids. The neolithic deposits found in the oued Tessalamane revealed the coexistence of both a terrestrial and an aquatic fauna that included crocodiles, molluscs and fish. This made evident that herding, hunting and fishing were complementary activities; numerous human skeletons lay mixed with food waste.
Grinding stones from the Neolithic lie disseminated in many places of the Sahara. The great quantity of them incited to think in the practice of an extensive agriculture, but the opinion of palynologists and biologists indicate that those served exclusively for grinding the wild graminaes, that were abundant in the ancient wet Sahara.
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