Believe it or not the Sahara Desert was once a savannah. It was covered with rivers and trees. And it was home to lots of different animals. So how did the green land turn to sand? Desertification - the spreading of deserts - is responsible for the change. But it didn't happen overnight and, in contrast to current climate change, it isn't attributable to man. German scientists believe the cause to be a tiny shift in Earth's orbit roughly 9,000 years ago. They think the shift changed the point of Earth's orbit closest to the sun increasing the number of hot sunny months and reducing the amount of rainfall in North Africa.