Short answers, pulled from the story.
The Sahara transformed from a verdant savanna into a hyper-arid desert over thousands of years between 11,000 and 5,000 years ago during the African Humid Period. This transformation was driven by the rhythmic precession of Earth's axis which shifted the North African monsoon southward. The region experienced lush vegetation and massive inland seas before the climate shifted and the waters receded.
Archaeological excavations at the Gobero site in the Ténéré Desert of Niger reveal the Kiffian culture which existed between 10,000 and 8,000 years ago and the Tenerian culture which emerged around 4600 BCE. Rock art in the Tassili n'Ajjer mountains of southeast Algeria contains over 30,000 petroglyphs depicting river animals and pastoral life that could only exist in a wet environment. The oldest mummy in Africa is a black Saharan child from Uan Muhuggiag dating back approximately 5,600 years.
The Garamantes civilization arose around 500 BCE in the Wadi al-Ajal valley of Fezzan, Libya and survived by digging tunnels far into the mountains to tap fossil water. This engineering feat allowed them to create a network of eight major towns and many other settlements in the desert. The civilization eventually collapsed after they had depleted the available water in the aquifers and could no longer sustain the effort to extend the tunnels further into the mountains.
The Sahara is the world's largest hot desert covering an area of 9.2 million square kilometers and spanning across North Africa from the Red Sea in the east to the Atlantic Ocean in the west. It is located in the horse latitudes under the subtropical ridge where air from the upper troposphere descends and prevents cloud formation. The Sahara is mainly rocky hamada with sand dunes forming only a minor part contrary to common misconception.
The Sahara supports around 2,800 species of vascular plants including acacia trees, palms, succulents, and spiny shrubs that have adapted to the arid conditions. The fauna includes the fennec fox, the addax, the dorcas gazelle, the Saharan cheetah, and the deathstalker scorpion which can be 5 centimeters long. Dromedary camels and goats are the domesticated animals most commonly found in the Sahara and the region also supports small populations of African wild dog and red-necked ostrich.