Anton Petrov discusses a recent study explaining the cyclical greening of the Sahara. He explains that the desert goes through predictable, extreme cycles of transitioning from a dry desert landscape to a green savanna every 21,000 years or so. Archaeological discoveries, such as cave paintings depicting floating humans and evidence of ancient lakes and animals such as hippos, confirm that the Sahara was not always a desert. The study linked this cycle to the Milankovitch precession cycle, a slight rocking of the Earth's axis that amplifies the West African monsoon, resulting in rains and greening of the region. This cycle of climate change has also been crucial to human migration and evolution out of Africa.