The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere.
In physical geography, the term hydrosphere (Greek hydro means "water") describes the collective mass of water found on, under, and over a planet's surface. The Earth's hydrosphere consists chiefly of the oceans, but technically includes clouds, inland seas, lakes, rivers, and underground waters.
Hydrosphere refers to that portion of Earth that is composed of water. The hydrosphere represents one component of Earth's system, operating in conjunction with the solid crust (lithosphere) and the air that envelopes the planet (atmosphere). The derivation of the term hydrosphere, from the Greek words for water and ball, is truly descriptive of our world, as it reflects the abundance and importance of water on Earth.
On Earth, water exists in the three primary states of matter; liquid, solid, and gas. The distance of Earth from the Sun, by fortunate coincidence, is such that the amount of energy arriving at the surface of most of the planet is sufficient to elevate the ambient temperature to levels above the freezing point of water, yet insufficient to cause all of the water to evaporate into the gaseous state. The capacity of water to store large quantities of heat energy heavily influences the nature of the global climate. The presence of large bodies of liquid water and the atmosphere restrict the range of temperature fluctuations on Earth. These conditions have allowed the existence of the fourth component of Earth's system, the biosphere.
Water is constantly being cycled through its various manifestations and through the components of Earth's systems by means of the hydrologic cycle. Driven by solar energy, water is evaporated from the ocean surface and distributed over the earth as water vapor. Precipitation returns the water, in liquid and solid forms, to other parts of the globe. Throughout the cycle, water may exist in a number of