• The Sahara sits atop the African Shield, which is made up of heavily folded and bare Precambrian rocks.
• Large areas are entirely empty, but wherever scant vegetation can support grazing animals or reliable water sources, scattered groups of residents have survived.
• Archaeological evidence suggests that the Sahara was increasingly inhabited by diverse populations, and the domestication of plants and animals led to professional specialization.

Sahara, (from Arabic ṣaḥrāʾ, “desert”) the largest desert in the world. Filling almost all of North Africa, it measures about 3,000 miles (4,800 km) from east to west and between 800 and 1,200 miles from north to south, and has a total area of ​​approximately 3,320,000 square miles ( 8,600,000 square km); the actual area varies as the desert expands and contracts over time. The Sahara is bordered on the west by the Atlantic Ocean, on the north by the Atlas Mountains and the Mediterranean Sea, on the east by the Red Sea and on the south by the Sahel, a semi-arid region that forms a transition zone between the Sahara in the north and the belt of humid savannas in the south.

PHYSIOGRAPHY

The main topographic features of the Sahara include seasonally flooded shallow basins (chotts and dayas) and large oasis depressions; vast plains covered with gravel (serirs or regs); rocky plateaus (hammadas); steep mountains; and sand sheets, dunes and seas of sand (ergs). The highest point in the desert is the 11,204-foot (3,415-meter) summit of Mount Koussi in the Tibesti Mountains of Chad. The lowest, at 436 feet (133 meters) below sea level, is in the Qattara Depression in Egypt.

The name Sahara derives from the Arabic name ṣaḥrāʾ, which means desert, and its plural, ṣaḥārāʾ. It is also linked to the adjective aṣḥar, meaning desert and carrying a strong connotation of the reddish color of plains without vegetation. There are also indigenous names for particular areas, such as the Tanezrouft region in southwest Algeria and the Ténéré region in central Niger, which are often of Berber origin.

The Sahara sits atop the African Shield, which is made up of heavily folded and bare Precambrian rocks. Due to the stability of the shield, the later deposited Paleozoic formations remained horizontal and relatively unchanged. Over much of the Sahara, these formations were covered with Mesozoic deposits – including limestones from Algeria, southern Tunisia, and northern Libya, and Nubian sandstones from the Libyan Desert – and numerous regional aquifers. important are identified there. In the northern Sahara, these formations are also associated with a series of basins and depressions stretching from the oases of western Egypt to the chotts of Algeria. In the south of the Sahara, the descending deformation of the African shield created large basins occupied by Cenozoic lakes and seas, like the old Mega-Chad. Serirs and regs differ in character in various parts of the desert, but are believed to represent Cenozoic deposit surfaces. An important feature of the plains is the dark patina of ferromanganese compounds, called desert varnish, which forms on the surface of weathered rocks. Sahara plateaus, such as the Tademait plateau in Algeria, are typically covered with angular and weathered rocks. In the central Sahara, the monotony of plains and plateaus is broken by prominent volcanic massifs, notably Mount Ê¿Uwaynat and the mountains of Tibesti and Ahaggar. Other notable formations include the Ennedi plateau in Chad, the Aïr massif in Niger, the Iforas massif in Mali and the outcrops of the Mauritanian region of Adrar.

Sand sheets and dunes cover about 25 percent of the surface of the Sahara. The main types of dunes include linked dunes, which form sheltered from hills or other obstacles; parabolic breaking dunes; crescent shaped barkhans and transverse dunes; longitudinal seifs; and the massive and complex shapes associated with seas of sand. Several pyramidal dunes in the Sahara reach heights of nearly 500 feet, while the draa, the mountainous sand ridges that dominate the ergs, are expected to reach 300 feet. An unusual phenomenon associated with desert sands is their “song” or explosion. Various hypotheses have been put forward to explain the phenomenon, such as those based on the piezoelectric property of crystalline quartz, but the mystery remains unsolved.

People

Although as large as the United States, the Sahara (excluding the Nile Valley) is estimated to have only some 2.5 million people, or less than one person per square mile (0.4 per square kilometer). Large areas are entirely empty, but wherever sparse vegetation can support grazing animals or reliable water sources, scattered groups of residents have survived in a fragile ecological balance with one of the harshest environments. tough people on the planet.

Long before recorded history, the Sahara was obviously more widely occupied. Stone artifacts, fossils and rock art, widely scattered in areas now far too dry to be occupied, reveal the ancient human presence, as well as that of game including antelopes, buffaloes, giraffes, elephants, rhinos and warthogs. Bone harpoons, shell accumulations and the remains of fish, crocodiles and hippos are associated with prehistoric settlements along the shores of ancient Saharan lakes. In some groups, hunting and fishing were subordinated to nomadic pastoralism, after the appearance of domesticated livestock in the Sahara nearly 7,000 years ago. Groups of cattle herders in the Ténéré region in Niger were said to have been either ancestral Berbers or ancestral Zaghawa; sheep and goats were apparently introduced by groups associated with the capsian culture of northeastern Africa. Direct evidence of agriculture first appeared about 6,000 years ago with the cultivation of barley and starch wheat in Egypt; these appear to have been introduced from Asia. Evidence of the domestication of native African plants is first found in pottery from around 1000 BCE discovered in Mauritania. Cultivators have been associated with the Gangara, the ancestors of the modern Soninke.

Archaeological evidence suggests that the Sahara was increasingly inhabited by diverse populations, and the domestication of plants and animals led to professional specialization. While the groups lived separately, the proximity of settlements suggests growing economic interdependence. Foreign trade has also developed. Copper from Mauritania had found its way to the Bronze Age civilizations of the Mediterranean in the 2nd millennium BCE. Trade intensified with the emergence of the Iron Age civilizations of the Sahara in the 1st century BCE, including the civilization centered in Nubia.

The greater mobility of the nomads facilitated their involvement in the trans-Saharan trade. The increasing aridity in the Sahara is documented in the transition from cattle and horses to camels. Although camels were used in Egypt in the 6th century BCE, their importance in the Sahara dates only to the 3rd century CE. The inhabitants of the Sahara oases were increasingly attacked by the Sanhaja (a Berber clan) and other nomads on camels, many of whom had entered the desert to avoid the anarchy and war of the end of the Roman period in North Africa. Many of the inhabitants of the remaining oases, among them the Haratin, were subjugated by the nomads. The expansion of Islam in North Africa between the 7th and 11th centuries prompted other groups of Berbers, as well as Arab groups wishing to retain their traditional beliefs, to settle in the Sahara. Islam eventually spread across trade routes, becoming the dominant social force in the wilderness.

Despite considerable cultural diversity, the peoples of the Sahara tend to be classified as pastoralists, sedentary farmers or specialists (such as blacksmiths associated in various ways with herders and cultivators). Pastoralism, still nomadic to some extent, occurs where there is sufficient scarce pasture, such as in marginal areas, on the edges of mountains and in the slightly wetter west. Cattle appear along the southern borders with the Sahel, but sheep, goats and camels are the mainstays of the desert. The main pastoral groups include the Regeibat of the northwestern Sahara and the Chaamba of the northern Algerian Sahara. Hierarchically structured, large pastoral groups once dominated the desert. Wars and raids (ghazw) were rampant, and during times of drought extensive migrations in search of pasture took place, resulting in heavy losses of animals. The Tuaregs (who call themselves Kel Tamasheq) were renowned for their warlike qualities and fierce independence. Although they are Islamic, they retain a matriarchal organization and Tuareg women have an unusual degree of freedom. Moorish groups in the west once had powerful tribal confederations. The Tedas, of Tibesti and its southern reaches, are mainly camel herders, renowned for their independence and physical endurance.

In the desert proper, sedentary occupation is limited to oases, where irrigation allows limited cultivation of date palm, pomegranate and other fruit trees; grains such as millet, barley and wheat; vegetables; and special crops such as henna. The culture is done in small “gardens”, maintained by a great expenditure of labor. Irrigation uses ephemeral streams in mountain areas, permanent ponds (gueltas), foggaras (inclined underground tunnels dug to collect the underground water dispersed in the beds of wadis), springs (Ê¿ayn) and wells (biʾr ). Some shallow groundwater is artesian, but it is often necessary to use water lifting devices. Old methods such as the shadoof (a pivoting pole and bucket) and animal-drawn noria (a Persian wheel with buckets) have been replaced by motorized pumps in more accessible oases. The availability of water strictly limits the expansion of the oases, and in some cases the overuse of water has resulted in a significant drop in the water level. Salinization of the soil by ferocious evaporation and burial by invading sand are other dangers.

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