Hydrosphere

[6][7][8] This includes water in gaseous, liquid and frozen forms as soil moisture, groundwater and permafrost in the Earth's crust (to a depth of 2 km); oceans and seas, lakes, rivers and streams, wetlands, glaciers, ice and snow cover on Earth's surface; vapour, droplets and crystals in the air; and part of living plants, animals and unicellular organisms of the biosphere.

The average salinity of Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%).

[10] According to Merriam Webster, the word hydrosphere was brought into English in 1887, translating the German term hydrosphäre, introduced by Eduard Suess.

Reservoirs include atmospheric moisture (snow, rain and clouds), streams, oceans, rivers, lakes, groundwater, subterranean aquifers, polar ice caps and saturated soil.

Solar energy, in the form of heat and light (insolation), and gravity cause the transfer from one state to another over periods from hours to thousands of years.

The hydrosphere is intricate, complex, interdependent, all-pervading, stable, and "seems purpose-built for regulating life.

"[12]: 26  De Villiers claimed that, "On earth, the total amount of water has almost certainly not changed since geological times: what we had then we still have.

These are the principal sources of fresh water to support life necessities and man's economic activities.

[notes 1] The hydrosphere plays an important role in the existence of the atmosphere in its present form.

Later, when cyanobacteria evolved, the process of conversion of carbon dioxide into food and oxygen began.

For instance, water diversion, human development, and pollution all affect the hydrosphere and natural processes within.

Additionally, only one third of rivers are free-flowing due to the extensive use of dams, levees, hydropower, and habitat degradation.

[17] Other ways humans impact the hydrosphere include eutrophication, acid rain, and ocean acidification.