The Sahara is the largest hot desert on Earth. It stretches across 9 million square kilometres of North Africa - larger than the entire United States, and big enough to cover Australia with room to spare. It crosses 11 different countries.
Six thousand years ago, though, the Sahara wasn’t a desert at all. It was a giant savanna covered in grass, dotted with rivers and lakes, and full of giraffes, hippos, and elephants. Ancient cave paintings deep inside the desert still show those animals.
A slow wobble in Earth’s tilt changed the African monsoon and dried the whole place out in just a few centuries. The same wobble means the Sahara will probably turn green again in another 10,000 years or so. Until then, it can hit 50°C by day and drop near freezing at night.
