Water and Life

Tides are the cyclic rising and falling of Earth’s ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams, making prediction of tides important for coastal navigation (see Navigation). The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides (see Intertidal ecology).

The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the bathymetry of oceans, seas and estuaries. Sea level measured by coastal tide gauges may also be strongly affected by wind. More generally, tidal phenomena can occur in other systems besides the ocean, whenever a gravitational field that varies in time and space is present

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in focus of ecohydrology.
The collective mass of water found on, under, and over the surface of a planet is called hydrosphere. Earth’s approximate water volume (the total water supply of the world) is 1 360 000 000 km³ (326 000 000 mi³). Of this volume:
•    1 320 000 000 km³ (316 900 000 mi³ or 97.2%) is in the oceans.
•    25 000 000 km³ (6 000 000 mi³ or 1.8%) is in glaciers, ice caps and ice sheets.
•    13 000 000 km³ (3,000,000 mi³ or 0.9%) is groundwater.
•    250 000 km³ (60,000 mi³ or 0.02%) is fresh water in lakes, inland seas, and rivers.
•    13 000 km³ (3,100 mi³ or 0.001%) is atmospheric water vapor at any given time.
Groundwater and fresh water are useful or potentially useful to humans as water resources.
Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor phases. It also exists as groundwater in aquifers.
The most important geological processes caused by water are: chemical weathering, water erosion, water sediment transport and sedimentation, mudflows, ice erosion and sedimentation by glacier.