Editing Hydrosphere (section)

{{Short description|Total amount of water on a planet}}
[[File:Ocean_world_Earth.jpg|thumb|upright=1.5|The [[Earth]] captured in the [[Pacific Ocean]] side]]

The '''hydrosphere''' ({{etymology|grc|''{{Wikt-lang|grc|ὕδωρ}}'' ({{grc-transl|ὕδωρ}})|water||''{{Wikt-lang|grc|σφαῖρα}}'' ({{grc-transl|σφαῖρα}})|sphere}})<ref>[https://wwwdoc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Du%28%2Fdwr ὕδωρ], Henry George Liddell, Robert Scott, ''[[A Greek-English Lexicon]]'', on [[Perseus Project|Perseus]]</ref><ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dsfai%3Dra^ σφαῖρα], Henry George Liddell, Robert Scott, ''[[A Greek-English Lexicon]]'', on [[Perseus Project|Perseus]]</ref> is the combined mass of [[water]] found on, under, and above the [[Planetary surface|surface]] of a [[planet]], [[minor planet]], or [[natural satellite]]. Although [[Earth]]'s hydrosphere has been around for about 4 billion years,<ref>Encyclopædia Britannica, 'Hydrosphere': https://www.britannica.com/science/hydrosphere/Origin-and-evolution-of-the-hydrosphere</ref><ref>{{cite journal |last1=Albarède |first1=Francis |last2=Blichert-Toft |first2=Janne |author2-link=Janne Blichert-Toft |title=The split fate of the early Earth, Mars, Venus, and Moon |journal=Comptes Rendus Geoscience |date=November 2007 |volume=339 |issue=14–15 |pages=917–927 |doi=10.1016/j.crte.2007.09.006 |bibcode=2007CRGeo.339..917A |url=https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.1016/j.crte.2007.09.006/ }}</ref> it continues to change in shape. This is caused by [[seafloor spreading]] and [[continental drift]], which rearranges the land and ocean.<ref name="Our Changing Planet 2011, pp. 88">"Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change." Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change, by Fred T. Mackenzie, 2nd ed., Pearson Education, 2011, pp. 88–91.</ref>

It has been estimated that there are 1.386 billion [[Cubic kilometer|cubic]] kilometres (333 million cubic miles) of water on Earth.<ref name="USGS">[https://web.archive.org/web/20131214091601/http://ga.water.usgs.gov/edu/earthwherewater.html Where is Earth's water?], [[United States Geological Survey]].</ref><ref>Eakins, B.W. and G.F. Sharman, [https://www.ncei.noaa.gov/products/etopo-global-relief-model Volumes of the World's Oceans from ETOPO1], [[NOAA]] [[National Geophysical Data Center]], [[Boulder, Colorado|Boulder, CO]], 2010.</ref><ref>[https://www.academia.edu/902661/Water_in_Crisis_Chapter_2_Oxford_University_Press_1993 Water in Crisis: Chapter 2], Peter H. Gleick, Oxford University Press, 1993.</ref> 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&nbsp;km); [[ocean]]s and [[List of seas|seas]], [[lake]]s, [[river]]s and [[stream]]s, [[wetland]]s, [[glacier]]s, 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. [[Saline water|Saltwater]] accounts for 97.5% of this amount, whereas [[fresh water]] accounts for only 2.5%. Of this fresh water, 68.9% is in the form of [[ice]] and permanent snow cover in the Arctic, the Antarctic and mountain [[glacier]]s; 30.8% is in the form of fresh groundwater; and only 0.3% of the fresh water on Earth is in easily accessible lakes, reservoirs and river systems.<ref name="Shiklomanov1998">{{cite report|url=http://webworld.unesco.org/water/ihp/publications/waterway/webpc/world_water_resources.html|title=World Water Resources: A New Appraisal and Assessment for the 21st Century|date=1998|publisher=UNESCO|access-date=13 June 2013|archive-url=https://web.archive.org/web/20130927160221/http://webworld.unesco.org/water/ihp/publications/waterway/webpc/world_water_resources.html|archive-date=27 September 2013|url-status=dead}}</ref>

The total mass of Earth's hydrosphere is about 1.4 × 10<sup>18</sup> [[tonnes]], which is about 0.023% of Earth's total mass. At any given time, about 2 × 10<sup>13</sup> tonnes of this is in the form of [[water vapor]] in the [[Atmosphere of Earth|Earth's atmosphere]] (for practical purposes, 1 cubic metre of water weighs 1 tonne). Approximately 71% of Earth's surface, an area of some 361 million square kilometres (139.5 million square miles), is covered by [[ocean]]. The average [[salinity]] of Earth's oceans is about 35&nbsp;grams of [[salt]] per kilogram of sea water (3.5%).<ref>{{cite book|first=Michael J.|last=Kennish|year=2001|title=Practical handbook of marine science|page=35|edition=3rd|publisher=CRC Press|series=Marine science series|isbn=0-8493-2391-6}}</ref>