ABSTRACT

W ATER continually moves around and above the earth as water vapor, liquid water, and ice. Moreover, water is continually changing its form. The earth is almost a "closed system," like a terrarium. That means that the earth, as a whole, neither gains nor loses much matter, including water. The water cycle (see Section 6.3) continually recycles water all around the globe, which means that the water we drink today was once used by our predecessors, in near time and very ancient time.87