"For several hundred thousand years, the Sahara has alternated between desert and savanna grassland in a 20,000-year cycle caused by the precession of Earth's a

"For several hundred thousand years, the Sahara has alternated between desert and savanna grassland in a 20,000-year cycle caused by the precession of Earth's axis (about 26,000 years) as it rotates around the Sun, which changes the location of the North African monsoon." https://en.wikipedia.org/wiki/Sahara#:~:text=For%20several%20hundred%20thousand%20years,of%20the%20North%20African%20monsoon https://en.wikipedia.org/wiki/Sahara#:~:text=For%20several%2....