Large parts of the Sahara Desert were green thousands of years ago, evidenced by prehistoric engravings in the desert of giraffes, crocodiles and a stone-age cave painting of humans swimming. Recently, more detailed insights were gained from a combination of sediment cores extracted from the Mediterranean Sea and results from climate computer modeling, which an international research team, including University of Hawai'i at Mānoa oceanography researcher Tobias Friedrich, examined for the first time.
source https://phys.org/news/2021-01-ancient-rivers-reveal-multiple-sahara.html
