Hydrosphere

Water is the most abundant substance on the surface of Earth. About 1.4 billion cubic km (326 million cubic miles) [blank] water in liquid and frozen form make up the oceans, lakes, streams, glaciers, and groundwaters found there. It is this enormous volume of water, in its various manifestations, that forms the discontinuous layer, enclosing [blank] of the terrestrial surface known as the hydrosphere. Central to any discussion of the hydrosphere is the concept of the water cycle (or hydrologic cycle). This cycle consists of a group of reservoirs containing water, the processes by which water is transferred [blank] one reservoir to another (or transformed from one state to another), and the rates of transfer associated [blank] such processes. These transfer paths penetrate the entire hydrosphere, extending upwards to about 15 km (9 miles) in Earth's atmosphere and downward [blank] depths on the order of 5 km (3 miles) in its crust.