Deserts

The Sahara (Arabic: الصحراء الكبرى‎ Aṣ Ṣaḥrā´ al Kubrā, English: The Great Desert) is the world's largest hot desert. At over 9,400,000 square kilometres (3,630,000 sq mi), it covers most of Northern Africa, making it almost as large as Europe or the United States. The only larger desert in the world is Antarctica, classified as such because of very low precipitation rates. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel, a belt of semi-arid tropical savanna that comprises the northern region of central and western Sub-Saharan Africa.
Some of the sand dunes can reach 180 metres (590 ft) in height.^[1] The name comes from the Arabic word for desert: (صَحراء), "ṣaḥrā´" ( صحراء (help·info); [sˤɑħrɑːʔ]).^[2][3]

The Sahara's boundaries 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 Air Mountains (a region of desert mountains and high plateaus), Ténéré desert and the Libyan desert (the most arid region). The highest peak in the Sahara is Emi Koussi (3,415 m/11,204 ft) 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.

People lived on the edge of the desert thousands of years ago^[4] since the last ice age. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles ^[5] 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.

People lived on the edge of the desert thousands of years ago^[4] since the last ice age. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles ^[5] 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.

Oasis in the Sahara Serto