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Sahara

2007 Schools Wikipedia Selection. Related subjects: African Geography;
Geography of the Middle East

   Satellite image
   Enlarge
   Satellite image

   The Sahara is the world's largest hot desert, and second largest desert
   at over 9,000,000 km² (3,500,000 mi²), almost as large as the United
   States. The Sahara is located in northern Africa and is 2.5 million
   years old.

Overview

   The top image shows the Safsaf Oasis on the surface of the Sahara. The
   bottom (using radar) is the rock layer underneath, revealing black
   channels cut by the meandering of an ancient river that once fed the
   oasis.
   Enlarge
   The top image shows the Safsaf Oasis on the surface of the Sahara. The
   bottom (using radar) is the rock layer underneath, revealing black
   channels cut by the meandering of an ancient river that once fed the
   oasis.

   The boundaries of the Sahara are the Atlantic Ocean on the west, the
   Atlas Mountains and the Mediterranean Sea on the north, the Red Sea and
   Egypt on the east, and the Sudan and the valley of the Niger River on
   the south. The Sahara is divided into western Sahara, the central
   Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains (a region
   of desert mountains and high plateaus), Tenere desert and the Libyan
   desert (the most arid region). The highest peak in the Sahara is Emi
   Koussi (3415 m) in the Tibesti Mountains in northern Chad.

   The Sahara divides the continent of Africa into North and Sub-Saharan
   Africa. The southern border of the Sahara is marked by a band of
   semiarid savanna called the Sahel; south of the Sahel lies the lusher
   Sudan and the Congo River Basin. Most of the Sahara consists of rocky
   hamada; ergs (large sand dunes) form only a minor part.

   Humans have lived on the edge of the desert for almost 500,000 years.
   Immediately after the last ice age, the Sahara was a much wetter place
   than it is today. Over 30,000 petroglyphs of river animals such as
   crocodiles (which still exist in parts of the desert) survive, with
   half found in the Tassili n'Ajjer in southeast Algeria. Fossils of
   dinosaurs, including Afrovenator, Jobaria and Ouranosaurus, have also
   been found here. The modern Sahara, though, is not as lush in
   vegetation, except in the Nile Valley, at a few oases, and in the
   northern highlands, where Mediterranean plants such as the olive tree
   are found to grow. The region has been this way since about 3000 BCE.

   Some 2.5 million people live in the Sahara, most of these in Egypt,
   Mauritania, Morocco and Algeria. Dominant ethnicities in the Sahara are
   various Berber groups including Tuareg tribes, various Arabised Berber
   groups such as the Hassaniya-speaking Maure/ Moors (also known as
   Sahrawis), and various "black African" ethnicities including Tubu,
   Nubians, Zaghawa, Kanuri, Peul (Fulani), Hausa and Songhai. The largest
   city in the Sahara is the Egyptian capital Cairo, in the Nile Valley.
   Other important cities are Nouakchott, the capital of Mauritania;
   Tamanrasset, Algeria; Timbuktu, Mali; Agadez, Niger; Ghat, Libya; and
   Faya, Chad.

Etymology

   Its name, Sahara, is an English pronunciation of the word for desert in
   Arabic, صحراء ).

Climate History

   The climate of the Sahara has undergone enormous variation between wet
   and dry over the last few hundred thousand years. During the last ice
   age, the Sahara was bigger than it is today, extending south beyond its
   current boundaries. The end of the ice age brought wetter times to the
   Sahara, from about 8000 BCE to 6000 BCE, perhaps due to low pressure
   areas over the collapsing ice sheets to the north.

   Once the ice sheets were gone, the northern part of the Sahara dried
   out. However, not long after the end of the ice sheets, the monsoon
   which currently brings rain to the Sahel came further north and
   counteracted the drying trend in the southern Sahara. The monsoon in
   Africa (and elsewhere) is due to heating during the summer. Air over
   land becomes warmer and rises, pulling in cool wet air from the ocean.
   This causes rain. So, paradoxically, the Sahara was wetter when it
   received more insolation in the summer. In turn, changes in solar
   insolation are caused by changes in the Earth's orbital parameters.

   By around 2500 BCE, the monsoon retreated south to approximately where
   it is today, leading to the desertification of the Sahara. The Sahara
   is currently as dry as it was about 13,000 years ago.

History

   The sun shines over Saharan dunes.
   Enlarge
   The sun shines over Saharan dunes.

Cattle Period

   By 6000 BCE predynastic Egyptians in the southwestern corner of Egypt
   were herding cattle and constructing large buildings. Subsistence in
   organized and permanent settlements in predynastic Egypt by the middle
   of the 6th millennium BCE centered predominantly on cereal and animal
   agriculture: cattle, goats, pigs and sheep. Metal objects replaced
   prior ones of stone. Tanning animal skins, pottery and weaving are
   commonplace in this era also. There are indications of seasonal or only
   temporary occupation of the Al Fayyum in the 6th millennium BCE, with
   food activities centering on fishing, hunting and food-gathering. Stone
   arrowheads, knives and scrapers are common. Burial items include
   pottery, jewelry, farming and hunting equipment, and assorted foods
   including dried meat and fruit. The dead are buried facing due west.

Berber Period

   The Phoenicians created a confederation of kingdoms across the entire
   Sahara to Egypt, generally settling on the coasts but sometimes in the
   desert also.

   By 2500 BCE the Sahara was as dry as it is today and it became a
   largely impenetrable barrier to humans, with only scattered settlements
   around the oases, but little trade or commerce through the desert. The
   one major exception was the Nile Valley. The Nile, however, was
   impassable at several cataracts making trade and contact difficult.

   Sometime between 633 and 530 BCE Hanno the Navigator either established
   or reinforced Phoenician colonies in the Western Sahara, but all
   ancient remains have vanished with virtually no trace. See History of
   Western Sahara.

Greeks

   By 500 BCE a new influence arrived in the form of the Greeks and
   Phoenicians. Greek traders spread along the eastern coast of the
   desert, establishing trading colonies along the Red Sea coast. The
   Carthaginians explored the Atlantic coast of the desert. The turbulence
   of the waters and the lack of markets never led to an extensive
   presence further south than modern Morocco. Centralized states thus
   surrounded the desert on the north and east; it remained outside of the
   control of these states. Raids from the nomadic Berber people of the
   desert were a constant concern of those living on the edge of the
   desert.

Urban civilization

   An urban civilization, the Garamantes, arose around this time in the
   heart of the Sahara, in a valley that is now called the Wadi al-Ajal in
   Fazzan, Libya. The Garamantes achieved this development by digging
   tunnels far into the mountains flanking the valley to tap fossil water
   and bring it to their fields. The Garamantes grew populous and strong,
   conquering their neighbors and capturing many slaves (which were put to
   work extending the tunnels). The ancient Greeks and the Romans knew of
   the Garamantes and regarded them as uncivilized nomads. However, they
   traded with the Garamantes, and a Roman bath has been found in the
   Garamantes capital of Garama. Archaeologists have found eight major
   towns and many other important settlements in the Garamantes territory.
   The Gartamantes civilization eventually collapsed after they had
   depleted available water in the aquifers, and could no longer sustain
   the effort to extend the tunnels still further into the mountains.

The Arabs

   After the Arab invasion of the Sahara, trade across the desert
   intensified. The kingdoms of the Sahel, especially the Ghana Empire and
   the later Mali Empire, grew rich and powerful exporting gold and salt
   to North Africa. The emirates along the Mediterranean sent south
   manufactured goods and horses. From the Sahara itself salt was
   exported. This process turned the scattered oasis communities into
   trading centres, and brought them under the control of the empires on
   the edge of the desert.

   This trade persisted for several centuries until the development in
   Europe of the caravel allowed ships, first from Portugal but soon from
   all Western Europe, to sail around the desert and gather the resources
   from the source in Guinea. The Sahara was rapidly remarginalized.

   The colonial powers also largely ignored the region, but the modern era
   has seen a number of mines and communities develop to exploit the
   desert's natural resources. These include large deposits of oil and
   natural gas in Algeria and Libya and large deposits of phosphates in
   Morocco and Western Sahara.

   mtDNA analyses found that various populations have contributed to the
   present-day gene pool of the Souss region of southern Morocco,
   including Berbers, Arabs, Phoenicians, Sephardic Jews, and sub-Saharan
   Africans. Throughout the Sahara, Berbers, Arabs, and sub-Saharan
   Africans are significantly represented genetically.

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