Hydrosphere

The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere.

A hydrosphere (from Greek ὕδωρ - hydor, "water" and σφαῖρα - sphaira, "sphere") in physical geography describes the combined mass of water found on, under, and over the surface of a planet.

The total mass of the Earth's hydrosphere is about 1.4 × 10¹⁸ tonnes, which is about 0.023% of the Earth's total mass. About 20 × 10¹² tonnes of this is in the Earth's atmosphere (the volume of one tonne of water is approximately 1 cubic metre). Approximately 75% of the Earth's surface, an area of some 361 million square kilometres (139.5 million square miles), is covered by ocean. The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (35 ‰).

Other hydrospheres

A thick hydrosphere is thought to exist around the Jovian moon Europa. The outer layer of this hydrosphere is almost entirely ice, but current models predict that there is an ocean up to 100 km in depth underneath the ice. This ocean remains in a liquid form because of tidal flexing of the moon in its orbit around Jupiter. The volume of Europa's hydrosphere is 3 × 10¹⁸ m³, 2.3 times that of Earth.

It has been suggested that the Jovian moon Ganymede and the Saturnian moon Enceladus may also possess sub-surface oceans. However the ice covering is expected to be thicker on Jupiter's Ganymede than on Europa. =]

Hydrological cycle

Insolation, or energy (in the form of heat and light) from the sun, provides the energy necessary to cause evaporation from all wet surfaces including oceans, rivers, lakes, soil and the leaves of plants. Water vapor is further released as transpiration from vegetation and from humans and other animals.

See also

• Biosphere
• Cryosphere
• Earth's atmosphere
• Lithosphere
• Ocean
• Pedosphere
• Table of global climate system components
• Water cycle

External links

• Ground Water - USGS