A desert is a place with 10 inches or 25cm of rain or less a year.
Deserts cover about one seventh of the earth's surface.
They are all extremely dry, and can be one of the harshest places on earth . Many deserts have extremes in temperature, with very high temperatures in the day and cold temperatures at night . Deserts are not only made of sand as many people think. They consist of rocks, mountains, and sand. Desert sands are often rock which has weathered down to sand over the centuries.