Sahara

Largest desert in the world, occupying around 9,065,000 sq km/3,500,000 sq mi of north Africa from the Atlantic to the Red Sea, with an interruption in the fertile Nile valley, covering: most of Egypt; part of west Sudan; large parts of Mauritania, Mali, Niger, and Chad; and southern parts of Morocco, Algeria, Tunisia, and Libya. Small areas in Algeria and Tunisia are below sea level, but it is mainly a plateau with a central mountain system, including the Ahaggar Mountains in Algeria, the Aïr Massif in Niger, and the Tibesti Massif in Chad, of which the highest peak is Emi Koussi, 3,415 m/11,208 ft.

Oases, often where water flowing underground from the rainy Atlas Mountains reaches the surface, punctuate the caravan routes, now modern roads. Resources include oil and gas in the north. Satellite observations have established a pattern below the surface of dried-up rivers that existed 2 million years ago. Cave paintings confirm that 4,000 years ago running rivers and animal life existed. Satellite photos taken during the 1980s have revealed that the Sahara expands and contracts from one year to another depending on rainfall; there is no continuous expansion, as had been believed.