Sahara Desert

The Sahara Desert covers approximately 9.2 million square kilometers across 11 African countries — roughly the size of the United States. It is the world's largest hot desert and one of Earth's most extreme environments, with temperatures ranging from -6°C to 58°C. Despite its reputation, only about 25% of the Sahara is sand dunes (ergs); the majority is rocky plateau (hamada). The Sahara was not always a desert — 10,000 years ago, during the African Humid Period, it was a green savanna with lakes, rivers, and diverse wildlife. Cave paintings show hippos, elephants, and cattle in regions now too dry for any life. Climate cycles and orbital changes transformed it to desert over millennia.