The term hydrosphere comes from the Greek words hydros (water) and sphaira (sphere). It is considered as the layer of the Earth formed by water, whether in a solid, liquid or gaseous state, and it is located on the earth's crust, covering three quarters (71%) of the Earth's surface.
The hydrosphere is made up mainly of oceans (which account for 94% of the Earth's water), as well as all the aquatic surfaces of the world, such as inland seas, rivers, lakes, streams, groundwater, glaciers, polar ice, snow mountains, water vapor, etc.
The total volume of water on Earth is 1,400 million cubic kilometers, most of it in the liquid state; in solid state there are only 29 million cubic kilometers. This volume of water is divided into salty water (oceans and seas), so called because it has a high content of common salt (NaCl); and in fresh water (rivers, lakes, ice and groundwater), which have less salt content.
These huge masses of water are in constant motion, especially due to the rotation and translation movements of the Planet and due to solar radiation, the reasons produced are due to various causes: marine currents, tidal waves, drift currents, caused by local winds and wave movements (waves).
Given that they cover most of the earth's surface, the oceans are the fundamental factor in defining the physical and chemical nature of this surface, for example, the climate is modified due to their ability to absorb solar energy and transport it around the planet. As well as through the evaporation-precipitation cycle, where the water evaporated from the oceans to the atmosphere falls as rain or snow on the continents, returning again to the sea through the rivers.
Likewise, the oceans have another important role, such as in regulating the oxygen and carbon dioxide contents involved in vital processes.
It should be noted that water is a natural resource necessary for the existence of life on the planet, currently the waters are threatened by pollution because societies use this resource as a means to eliminate their waste.
