Nature

===Oceans===
[[File:Ocean from Leblon.jpg|thumb|left|A view of the Atlantic Ocean from [[Leblon]], Rio de Janeiro]]
{{Main|Ocean}}
An ocean is a major body of [[Seawater|saline water]], and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (an area of some 361 million square kilometers) is covered by ocean, a [[World Ocean|continuous body of water]] that is customarily divided into several principal oceans and smaller seas. More than half of this area is over {{convert|3000|m|ft|abbr=off|sp=us}} deep. Average oceanic [[salinity]] is around 35 [[parts per thousand]] (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt. Though generally recognized as several 'separate' oceans, these waters comprise one global, interconnected body of salt water often referred to as the [[World Ocean]] or global ocean.<ref>"[http://www.answers.com/Ocean#Encyclopedia Ocean] {{Webarchive|url=https://web.archive.org/web/20110126035624/http://www.answers.com/topic/ocean#Encyclopedia |date=January 26, 2011 }}". ''The Columbia Encyclopedia.'' 2002. New York: Columbia University Press</ref><ref name="UNAoO">"[http://www.oceansatlas.com/unatlas/about/physicalandchemicalproperties/background/seemore1.html Distribution of land and water on the planet] {{webarchive|url=https://web.archive.org/web/20080531103749/http://www.oceansatlas.com/unatlas/about/physicalandchemicalproperties/background/seemore1.html |date=May 31, 2008 }}". [http://www.oceansatlas.com/ UN Atlas of the Oceans] {{Webarchive|url=https://web.archive.org/web/20080915105349/http://www.oceansatlas.com/ |date=September 15, 2008 }}</ref> This concept of a global ocean as a continuous body of water with relatively free interchange among its parts is of fundamental importance to [[oceanography]].<ref>{{cite journal | last1 = Spilhaus | first1 = Athelstan F | year = 1942 | title = Maps of the whole world ocean | journal = Geographical Review | volume = 32 | issue = 3| pages = 431–435 | doi=10.2307/210385| jstor = 210385 | bibcode = 1942GeoRv..32..431S }}</ref>

The major oceanic divisions are defined in part by the [[continent]]s, various [[archipelago]]s, and other criteria: these divisions are (in descending order of size) the [[Pacific Ocean]], the [[Atlantic Ocean]], the [[Indian Ocean]], the [[Southern Ocean]], and the [[Arctic Ocean]]. Smaller regions of the oceans are called seas, gulfs, [[bay]]s and other names. There are also [[salt lake]]s, which are smaller bodies of landlocked saltwater that are not interconnected with the World Ocean. Two notable examples of salt lakes are the [[Aral Sea]] and the [[Great Salt Lake]].