3. Free electives: Free electives are courses in addition to the Core Curriculum and major requirements sufficient to reach a minimum of 120 credit hours for graduation. Students may graduate with more but not less than 120 credit hours.
Evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling and evaporates before reaching the ground. Rainfall is lowest on the Atacama Desert of Chile, where it averages less than 1.5 cm. Some years are even rainless. Inland Sahara also receives less than 1.5 cm a year. Rainfall in American deserts is higher  almost 28 cm a year.
A desert is a landscape or region that receives very little precipitation - less than 250 mm per year (about ten inches). Approximately 1/3 of Earth's land surface is a desert. There are four different types of deserts based upon their geographic situation: 1) polar deserts; 2) subtropical deserts, 3) cold winter deserts, and 4) cool coastal deserts. As shown on the map above, deserts occur on all of Earth's continents.