Background Information: The Hydrologic Cycle

The hydrologic cycle is the cycle through which water passes from sea to land and from land to sea. Water vapor enters the air through the evaporation of water. Water vapor in the air eventually condenses and falls as rain, snow, sleet, or hail. Water that falls on land collects in rivers which carry it back to the ocean. The return of water to the ocean may be slowed when water becomes trapped in lakes, swamps, or openings in the rocks. However, most water returns to the ocean.

The water cycle is the cycle where water is continuously carried from ocean to land to ocean again.

Origin of the Ocean

It is interesting to consider the events which led to the formation of the world's oceans although the present knowledge is not perfect. An individual ocean grows from an initial rift, reaching a maximum size, then shrinks, and ultimately closes completely. The question of the origin of the ocean is really two problems: (a) from where did the water come and (b) how did it get its unique concentration of elements? Concerning the water on earth, there are three hypotheses to explain its origin:

• From the primordial atmosphere of the earth
• From the decomposition of volcanic rock
• From the incremental addition of water throughout geologic time.