Sahara Desert, Africa

The Sahara (Arabic: الصحراء الكبرى‎, aṣ-Ṣaḥrāʾ al-Kubrā , 'the Great Desert') is the world's hottest desert, and the third largest desert after Antarctica and the Arctic. At over 9,400,000 square kilometres (3,600,000 sq mi), it covers most of North Africa, making it almost as large as China or the United States. 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 composes the northern region of central and western Sub-Saharan Africa.

 The Sahara's boundaries are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean on the north, the Red Sea on the east, and the Sudan (region) 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), Ténéré desert and the Libyan Desert (the most arid region). The highest peak in the Sahara is Emi Koussi (3,415 metres (11,204 ft)) in the Tibesti Mountains in northern Chad. The Sahara is the largest desert on the African continent. The southern border of the Sahara is marked by a band of semiarid savanna called the Sahel; south of the Sahel lies Southern Sudan and the Congo River Basin. Most of the Sahara consists of rocky hamada; ergs (large areas covered with sand dunes) form only a minor part. People lived on the edge of the desert thousands of years ago 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  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 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 1600 BC, after shifts in the Earth's axis increased temperatures and decreased precipitation.[9] Then, due to a climate change, the savannah changed into the sandy desert as we know it now..
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