When the Sahara was Green

Apparently the Sahara has not always been a searing wilderness with little to zero rainfall but was once a vast savanna, reminiscent of grasslands of the Serengeti. And I don’t mean just a few years of extra showers of rain, I mean a climate that was so wet for so long that humans and animals made themselves at home in the Sahara. The mystery therefore is HOW and WHEN this lush grassland turned into the barren wasteland we see today.