## TL;DR

The Sahara Desert (9.2 million km²) is the world's largest hot desert, spanning 11 North African countries. Contrary to perception, only ~25% is sand — most is rock/gravel plateaus (hamada). Once a green savannah (African Humid Period, 10,000-5,000 years ago) with lakes and wildlife.

## Core Explanation

Climate: extreme temperatures (day 50°C+, night near freezing). Rain: <25mm/year in driest areas. Dust: Sahara is Earth's largest dust source — fertilizes Amazon rainforest across Atlantic. Oases: underground water sources sustain life. Sahara expands/contracts with climate cycles (currently growing ~10% per century). Tuareg: nomadic 'Blue People' of the Sahara.

## Further Reading

- [Sahara: A Natural History (de Villiers & Hirtle)](https://www.bloomsbury.com/us/sahara-9780802713568/)