When the Sahara Was Green

The Sahara, today the largest hot desert on Earth, was green and lush just 5,000 years ago, with hippos and crocodiles in its lakes. Ancient rock art in the Tassili mountains shows giraffes, elephants and people swimming. A slow shift in the orbit of Earth switched monsoon rains off around 3000 BC, and grasslands gave way to the 9,200,000 square km sand sea of today, where summer highs regularly exceed 45C.

Only the polar deserts are bigger: Antarctic Desert spans 14,200,000 square km, while the Rub al Khali in the Arabian Desert holds the largest continuous sand body at 650,000 square km..