Formation of the Sahara

How did the mighty Sahara Desert form? This huge desert, the largest in the world not counting the Arctic or Antartica, covers roughly 10% of Africa. How does such a structure form? According to this article: (http://www.sci-news.com/othersciences/paleoclimatology/science-sahara-desert-formed-7-million-years-ago-02160.html) the region in the north of Africa first started experiencing desertification over 7 million years ago during the Tortonian stage (7-11 million years ago). Before this time, Africa was bordered by the Tethys sea. This sea brought this region of Africa plenty of moisture, and allowed lush vegetation and deep soils to grow. Due to the cycles in climate and the movement of tectonic plates, the Tethys sea eventually dried out, and the region of the great desert became susceptible to arid conditions.

The nail in the coffin was the changing┬átilt of the Earth’s axis. The tilt used to be more severe around 5000 years ago. When the tilt decreased in severity the upper region of Africa stopped getting large monsoons, an important part of the ecosystem and vegetation that depended on the annual water surplus. Without these monsoons, plants couldn’t survive, soils couldn’t grow, and the Sahara began to form.