> Long, long ago, the Sahara was not quite so dry as it is now. There were rivers then, which have dried up since. When there was water, food would grow, and people could keep sheep and cattle. In those days there were several large cities there. But when the water began to dry up, the ground became sandy and nothing would grow. Then, whenever the wind blew, the sand was carried along and began to cover up the houses and temples. The people had moved away because their food would not grow, and soon the sand completely covered the old cities.

I'd be worried.