The Sahara has an intermittent history that may go back as much as 3 million years. Some of the sand dunes can reach 180 meters (600 ft) in height. The name comes from the Arabic word for desert: (صَحراء), "ṣaḥrā´" (صحراء).

Overview

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 agoDiscover Magazine, 2006-Oct. 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 National Geographic News, 2006-06-17. 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 5000 BP. Some 2.5 million people currently 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. Important cities located in the Sahara include Nouakchott, the capital of Mauritania; Tamanrasset, Ouargla, Bechar, Hassi Messaoud, Ghardaia, El Oued, Algeria; Timbuktu, Mali; Agadez, Niger; Ghat, Libya; and Faya-Largeau, Chad.

It has been reported that the Sahara is expanding south by as much as per year, overwhelming degraded grasslands,Sahara Expanding, accessed on April 20, 2008 Sahara, accessed on April 20, 2008 taking over the Sahel, the dry tropical savanna that has defined the Sahara's southern limit. Global warming and poor farming methods have been given as possible causes.http://www.csmonitor.com/2005/0801/p01s02-woaf.html Hunger is spreading in Africa, accessed on April 20, 2008 The spreading of deserts is known as "desertification," and the phenomenon is occurring in other desert areas worldwide.