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{{Short description|Natural, physical, or material world and its phenomena}}
{{Redirect|Natural|other uses|Natural (disambiguation)|and|Nature (disambiguation)}}
{{Pp-semi-indef|small=yes}}
{{Good article}}
{{Use mdy dates|date=September 2018}}
[[File:Startrails above Gunung Bromo - Indonesia.jpg|upright=1.3|thumb|A timelapse composite panorama of different natural phenomena and environments around [[Mount Bromo]], Indonesia.]]

'''Nature''' is an inherent character or constitution,<ref name="Merriam-Webster 2024 d901">{{cite web | title=Definition of NATURE | website=Merriam-Webster | date=January 2, 2024 | url=https://www.merriam-webster.com/dictionary/nature | access-date=January 7, 2024}}</ref> particularly of the [[Ecosphere (planetary)|ecosphere]] or the [[universe]] as a whole. In this general sense nature refers to the [[Scientific law|laws]], elements and [[phenomenon|phenomena]] of the physical world, including [[life]]. Although humans are part of nature, human activity or humans as a whole are often described as at times at odds, or outright [[Anthropocentrism|separate and even superior]] to nature.<ref name="What does nature mean"/>

During the advent of modern [[scientific method]] in the last several centuries, nature became the passive [[reality]], organized and moved by divine laws.<ref>Isaac Newton's [[Philosophiae Naturalis Principia Mathematica]] (1687), for example, is translated "Mathematical Principles of Natural Philosophy", and reflects the then-current use of the words "[[natural philosophy]]", akin to "systematic study of nature"</ref><ref>The etymology of the word "physical" shows its use as a synonym for "natural" in about the mid-15th century: {{OEtymD|physical|access-date=September 20, 2006}}</ref> With the [[Industrial revolution]], nature increasingly became seen as the part of reality deprived from intentional intervention: it was hence considered as sacred by some traditions ([[Jean-Jacques Rousseau|Rousseau]], American [[transcendentalism]]) or a mere decorum for [[divine providence]] or human history ([[Hegel]], [[Marx]]). However, a [[vitalist]] vision of nature, closer to the pre-Socratic one, got reborn at the same time, especially after [[Charles Darwin]].<ref name="What does nature mean" />

Within the various uses of the word today, "nature" often refers to [[geology]] and [[wildlife]]. Nature can refer to the general realm of living plants and animals, and in some cases to the processes associated with inanimate objects—the way that particular types of things exist and change of their own accord, such as the weather and geology of the [[Earth]]. It is often taken to mean the "[[natural environment]]" or [[wilderness]]—wild animals, rocks, forest, and in general those things that have not been substantially altered by human intervention, or which persist despite human intervention. For example, manufactured objects and human interaction generally are not considered part of nature, unless qualified as, for example, "human nature" or "the whole of nature". This more traditional concept of natural things that can still be found today implies a distinction between the natural and the artificial, with the artificial being understood as that which has been brought into being by a human [[consciousness]] or a human [[mind]]. Depending on the particular context, the term "natural" might also be distinguished from the [[Wikt:unnatural|unnatural]] or the [[supernatural]].<ref name="What does nature mean"/>

==Etymology==
The word ''nature'' is borrowed from the [[Old French]] ''nature'' and is derived from the [[Latin]] word ''natura'', or "essential qualities, innate disposition", and in ancient times, literally meant "[[birth]]".<ref name="etymonline-nature">{{OEtymD|nature|access-date=September 23, 2006}}</ref> In ancient philosophy, ''natura'' is mostly used as the Latin translation of the Greek word ''[[physis]]'' (φύσις), which originally related to the intrinsic characteristics of plants, animals, and other features of the world to develop of their own accord.<ref>An account of the pre-Socratic use of the concept of φύσις may be found in Naddaf, Gerard (2006) ''The Greek Concept of Nature'', SUNY Press, and in {{cite journal |last1=Ducarme |first1=Frédéric |last2=Couvet |first2=Denis |year=2020 |title=What does 'nature' mean? |journal=[[Palgrave Communications]] |volume=6 |issue=14 |publisher=[[Springer Nature]] |doi=10.1057/s41599-020-0390-y |doi-access=free }}. The word φύσις, while first used in connection with a plant in Homer, occurs early in Greek philosophy, and in several senses. Generally, these senses match rather well the current senses in which the English word ''nature'' is used, as confirmed by Guthrie, W.K.C. ''Presocratic Tradition from Parmenides to Democritus'' (volume 2 of his ''History of Greek Philosophy''), Cambridge UP, 1965.</ref><ref>The first known use of ''physis'' was by [[Homer]] in reference to the intrinsic qualities of a plant: ὣς ἄρα φωνήσας πόρε φάρμακον ἀργεϊφόντης ἐκ γαίης ἐρύσας, καί μοι '''φύσιν''' αὐτοῦ ἔδειξε. (So saying, Argeiphontes [=Hermes] gave me the herb, drawing it from the ground, and showed me its '''nature'''.) ''[[Odyssey]]'' 10.302–303 (ed. A.T. Murray). (The word is dealt with thoroughly in Liddell and Scott's ''[http://archimedes.fas.harvard.edu/pollux Greek Lexicon] {{Webarchive|url=https://web.archive.org/web/20110305235638/http://archimedes.fas.harvard.edu/pollux/ |date=March 5, 2011 }}''.) For later but still very early Greek uses of the term, see earlier note.</ref>
The concept of nature as a whole, the physical [[universe]], is one of several expansions of the original notion;<ref name="What does nature mean">{{cite journal |last1=Ducarme |first1=Frédéric |last2=Couvet |first2=Denis |year=2020 |title=What does 'nature' mean? |journal=[[Palgrave Communications]] |volume=6 |issue=14 |publisher=[[Springer Nature]] |doi=10.1057/s41599-020-0390-y |doi-access=free }}</ref> it began with certain core applications of the word φύσις by [[Pre-Socratic philosophy|pre-Socratic]] philosophers (though this word had a dynamic dimension then, especially for [[Heraclitus]]), and has steadily gained currency ever since.

==Earth==
{{Nature timeline}}
{{Main|Earth|Earth science}}
[[File:The Earth seen from Apollo 17.jpg|thumb|left|''[[The Blue Marble]]'', which is a famous view of the [[Earth]], taken in 1972 by the crew of [[Apollo 17]]]]
Earth is the only [[planet]] known to support [[life]], and its natural features are the subject of many fields of scientific research. Within the [[Solar System]], it is third closest to the Sun; it is the largest [[terrestrial planet]] and the fifth largest overall. Its most prominent climatic features are its two large polar regions, two relatively narrow [[temperate]] zones, and a wide [[equator]]ial tropical to [[subtropical]] region.<ref>
{{cite web
|url=http://www.blueplanetbiomes.org/climate.htm
|title=World Climates
|work=Blue Planet Biomes
|access-date=September 21, 2006
|archive-url=https://web.archive.org/web/20081217015636/http://www.blueplanetbiomes.org/climate.htm
|archive-date=December 17, 2008
|url-status=live
|df=mdy-all
}}
</ref> [[Precipitation]] varies widely with location, from several metres of water per year to less than a millimetre. 71 percent of the Earth's surface is covered by salt-water oceans. The remainder consists of continents and islands, with most of the inhabited land in the [[Northern Hemisphere]].

Earth has evolved through geological and biological processes that have left traces of the original conditions. The [[Crust (geology)|outer surface]] is divided into several gradually migrating [[tectonic plate]]s. The interior remains active, with a thick layer of plastic [[Mantle (geology)|mantle]] and an iron-filled core that generates a [[magnetic field]]. This iron core is composed of a solid inner phase, and a fluid outer phase. Convective motion in the core generates electric currents through dynamo action, and these, in turn, generate the geomagnetic field.

The [[atmosphere|atmospheric]] conditions have been significantly altered from the original conditions by the presence of life-forms,<ref>{{cite web|date = September 11, 2005|url = https://www.sciencedaily.com/releases/2005/09/050911103921.htm|title = Calculations favor reducing atmosphere for early Earth|work = [[Science Daily]]|access-date = January 6, 2007|archive-url = https://web.archive.org/web/20060830150624/http://www.sciencedaily.com/releases/2005/09/050911103921.htm|archive-date = August 30, 2006|url-status=live|df = mdy-all}}</ref> which create an ecological balance that stabilizes the surface conditions. Despite the wide regional variations in climate by [[latitude]] and other geographic factors, the long-term average global climate is quite stable during interglacial periods,<ref>{{cite web|url = http://www.epa.gov/climatechange/science/pastcc.html|title = Past Climate Change|publisher = U.S. Environmental Protection Agency|access-date = January 7, 2007|archive-url = https://web.archive.org/web/20120511021842/http://www.epa.gov/climatechange/science/pastcc.html|archive-date = May 11, 2012|url-status=live|df = mdy-all}}</ref> and variations of a degree or two of average global temperature have historically had major effects on the ecological balance, and on the actual geography of the Earth.<ref>{{cite web|author=Hugh Anderson|author2=Bernard Walter|date = March 28, 1997|url = http://vathena.arc.nasa.gov/curric/land/global/climchng.html |title = History of Climate Change|publisher = NASA|access-date = January 7, 2007 |url-status=dead|archive-url = https://web.archive.org/web/20080123130745/http://vathena.arc.nasa.gov/curric/land/global/climchng.html |archive-date = January 23, 2008}}</ref><ref>{{cite web|last = Weart|first = Spencer|date = June 2006|url = http://www.aip.org/history/climate/|title = The Discovery of Global Warming|publisher = American Institute of Physics|access-date = January 7, 2007|archive-url = https://web.archive.org/web/20110804232058/http://www.aip.org/history/climate/|archive-date = August 4, 2011|url-status=live|df = mdy-all}}</ref>

===Geology===
{{Main|Geology}}
Geology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, [[structural geology|structure]], [[Physical property|physical properties]], dynamics, and [[History of the Earth|history]] of [[Earth materials]], and the processes by which they are formed, moved, and changed. The field is a major [[academic discipline]], and is also important for [[mining|mineral]] and [[petroleum geology|hydrocarbon]] extraction, knowledge about and mitigation of [[natural hazard]]s, some [[Geotechnical engineering]] fields, and understanding [[Paleoclimatology|past climates]] and environments.

====Geological evolution====
[[File:Tectonic plate boundaries.png|thumb|left|upright=1.3|Three types of geological [[plate tectonic]] boundaries]]
The geology of an area evolves through time as rock units are deposited and inserted and deformational processes change their shapes and locations.

Rock units are first emplaced either by [[deposition (geology)|deposition]] onto the surface or intrude into the [[Country rock (geology)|overlying rock]]. Deposition can occur when [[sediment]]s settle onto the surface of the Earth and later [[lithification|lithify]] into [[sedimentary rock]], or when as [[volcanic rock|volcanic material]] such as [[volcanic ash]] or [[lava]] flows, blanket the surface. Igneous [[intrusion]]s such as [[batholith]]s, [[laccolith]]s, [[dike (geology)|dikes]], and [[sill (geology)|sills]], push upwards into the overlying rock, and crystallize as they intrude.

After the initial sequence of rocks has been deposited, the rock units can be [[deformation (mechanics)|deformed]] and/or [[metamorphism|metamorphosed]]. Deformation typically occurs as a result of horizontal shortening, [[extension (geology)|horizontal extension]], or side-to-side ([[strike-slip]]) motion. These structural regimes broadly relate to [[convergent boundary|convergent boundaries]], [[divergent boundary|divergent boundaries]], and [[transform boundary|transform boundaries]], respectively, between [[plate tectonics|tectonic plates]].

===Historical perspective===
{{Main|History of the Earth|Evolution}}
[[File:Pangea animation 03.gif|thumb|300px|An animation showing the movement of the continents from the separation of [[Pangaea]] until the present day]]
<!-- Images End -->
Earth is estimated to have formed 4.54&nbsp;billion years ago from the [[solar nebula]], along with the [[Sun]] and other [[planet]]s.<ref>{{cite book |first=G. Brent |last=Dalrymple |date=1991 |title=The Age of the Earth |publisher=Stanford University Press |location=Stanford |isbn=978-0-8047-1569-0}}</ref> The Moon formed roughly 20&nbsp;million years later. Initially molten, the outer layer of the Earth cooled, resulting in the solid crust. Outgassing and [[Volcano|volcanic]] activity produced the primordial atmosphere. Condensing [[water vapor]], most or all of which came from [[ice]] delivered by [[comet]]s, [[Origin of water on Earth|produced the oceans]] and other water sources.<ref>
{{cite journal|first=A.|last=Morbidelli|display-authors=etal|date=2000|bibcode=2000M&PS...35.1309M|title=Source Regions and Time Scales for the Delivery of Water to Earth|journal=Meteoritics & Planetary Science|volume=35|issue=6|pages=1309–1320|doi=10.1111/j.1945-5100.2000.tb01518.x|doi-access=free}}</ref> The highly energetic chemistry is believed to have produced a self-replicating molecule around 4&nbsp;billion years ago.<ref>
{{cite news|title=Earth's Oldest Mineral Grains Suggest an Early Start for Life|publisher=NASA Astrobiology Institute|date=December 24, 2001|url=http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=76|access-date=May 24, 2006|url-status=dead|archive-url=https://web.archive.org/web/20060928231649/http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=76|archive-date=September 28, 2006}}</ref>
[[File:Hyperia.jpg|thumb|left|[[Plankton]] inhabit oceans, seas and lakes, and have existed in various forms for at least 2&nbsp;billion years.<ref name="Margulis1995">{{cite book|last=Margulis|first=Lynn|author-link=Lynn Margulis|author2=Dorian Sagan|date=1995|title=What is Life?|publisher=Simon & Schuster|location=New York|isbn=978-0-684-81326-4|url=https://archive.org/details/isbn_9780684810874}}</ref>]]
Continents formed, then broke up and reformed as the surface of Earth reshaped over hundreds of millions of years, occasionally combining to make a [[supercontinent]]. Roughly 750&nbsp;million years ago, the earliest known supercontinent [[Rodinia]], began to break apart. The continents later recombined to form [[Pannotia]] which broke apart about 540&nbsp;million years ago, then finally [[Pangaea]], which broke apart about 180&nbsp;million years ago.<ref>{{cite journal |first=J.B. |last=Murphy |author2=R.D. Nance |date=2004 |url=http://www.americanscientist.org/issues/page2/how-do-supercontinents-assemble |title=How do supercontinents assemble? |journal=American Scientist |volume=92 |issue=4 |doi=10.1511/2004.4.324 |page=324 |access-date=August 23, 2010 |archive-url=https://web.archive.org/web/20110128224011/http://www.americanscientist.org/issues/page2/how-do-supercontinents-assemble |archive-date=January 28, 2011 |url-status=live |df=mdy-all }}</ref>

During the [[Neoproterozoic]] era, freezing temperatures covered much of the Earth in [[glacier]]s and ice sheets. This hypothesis has been termed the "[[Snowball Earth]]", and it is of particular interest as it precedes the [[Cambrian explosion]] in which multicellular life forms began to proliferate about 530–540&nbsp;million years ago.<ref>{{cite book |first=J.L. |last=Kirschvink |date=1992 |chapter=Late Proterozoic Low-Latitude Global Glaciation: The Snowball Earth |chapter-url=http://www.gps.caltech.edu/~jkirschvink/pdfs/firstsnowball.pdf |title=The Proterozoic Biosphere |editor=J.W. Schopf |editor2=C. Klein |publisher=Cambridge University Press |location=Cambridge |pages=51–52 |isbn=978-0-521-36615-1}}</ref>

Since the Cambrian explosion there have been five distinctly identifiable [[Extinction event|mass extinctions]].<ref>{{cite journal |last=Raup |first=David M. |author2=J. John Sepkoski Jr. |date=March 1982 |title=Mass extinctions in the marine fossil record |journal=Science |volume=215 |issue=4539|pages = 1501–1503 |doi=10.1126/science.215.4539.1501 |pmid=17788674 |bibcode=1982Sci...215.1501R|s2cid=43002817 }}</ref> The last mass extinction occurred some 66 million years ago, when a meteorite collision probably triggered the extinction of the [[Bird|non-avian]] [[dinosaur]]s and other large reptiles, but spared small animals such as [[mammal]]s. Over the past 66&nbsp;million years, mammalian life diversified.<ref>{{cite book |last=Margulis |first=Lynn |author2=Dorian Sagan |date=1995 |title=What is Life? |publisher=Simon & Schuster |location=New York |isbn=978-0-684-81326-4 |page=[https://archive.org/details/isbn_9780684810874/page/145 145] |url=https://archive.org/details/isbn_9780684810874/page/145 }}</ref>

Several million years ago, a species of small African [[ape]] gained the ability to stand upright.<ref name="Margulis1995" /> The subsequent advent of human life, and the development of agriculture and further [[civilization]] allowed humans to affect the Earth more rapidly than any previous life form, affecting both the nature and quantity of other organisms as well as global climate. By comparison, the [[Great Oxygenation Event]], produced by the proliferation of [[algae]] during the [[Siderian]] period, required about 300&nbsp;million years to culminate.

The present era is classified as part of a mass [[extinction event]], the [[Holocene extinction]] event, the fastest ever to have occurred.<ref>{{cite journal|author = Diamond J|title = The present, past and future of human-caused extinctions|journal = Philos Trans R Soc Lond B Biol Sci|volume = 325|issue = 1228|pages = 469–476; discussion 476–477|date = 1989|pmid = 2574887|doi = 10.1098/rstb.1989.0100|last2 = Ashmole|first2 = N. P.|last3 = Purves|first3 = P. E.|bibcode = 1989RSPTB.325..469D|doi-access = }}</ref><ref>{{cite journal|author = Novacek M|author2 = Cleland E|title = The current biodiversity extinction event: scenarios for mitigation and recovery|journal = Proc Natl Acad Sci USA|volume = 98|issue = 10|date = 2001|pmid = 11344295|doi = 10.1073/pnas.091093698|pmc = 33235|bibcode = 2001PNAS...98.5466N|pages = 5466–5470|doi-access = free}}</ref> Some, such as [[E. O. Wilson]] of [[Harvard University]], predict that human destruction of the [[biosphere]] could cause the extinction of one-half of all species in the next 100&nbsp;years.<ref>{{cite journal|title=The mid-Holocene extinction of silver fir (Abies alba) in the Southern Alps: a consequence of forest fires? Palaeobotanical records and forest simulations|doi=10.1007/s00334-006-0051-0|date=2006|last1=Wick|first1=Lucia|last2=Möhl|first2=Adrian|journal=Vegetation History and Archaeobotany|volume=15|issue=4|pages=435–444|s2cid=52953180|url=http://doc.rero.ch/record/309852/files/334_2006_Article_51.pdf|access-date=November 15, 2018|archive-url=https://web.archive.org/web/20181115113137/http://doc.rero.ch/record/309852/files/334_2006_Article_51.pdf|archive-date=November 15, 2018|url-status=live|df=mdy-all}}</ref> The extent of the current extinction event is still being researched, debated and calculated by biologists.<ref>[http://park.org/Canada/Museum/extinction/holmass.html The Holocene Extinction] {{Webarchive|url=https://web.archive.org/web/20060925041056/http://park.org/Canada/Museum/extinction/holmass.html |date=September 25, 2006 }}. Park.org. Retrieved on November 3, 2016.</ref><ref>[http://park.org/Canada/Museum/extinction/extincmenu.html Mass Extinctions Of The Phanerozoic Menu] {{Webarchive|url=https://web.archive.org/web/20060925030659/http://park.org/Canada/Museum/extinction/extincmenu.html |date=September 25, 2006 }}. Park.org. Retrieved on November 3, 2016.</ref><ref>[http://park.org/Canada/Museum/extinction/patterns.html Patterns of Extinction] {{Webarchive|url=https://web.archive.org/web/20060925024739/http://park.org/Canada/Museum/extinction/patterns.html |date=September 25, 2006 }}. Park.org. Retrieved on November 3, 2016.</ref>
{{clear right}}

==Atmosphere, climate, and weather==
[[File:Top of Atmosphere.jpg|thumb|[[Rayleigh scattering|Blue light is scattered more]] than other wavelengths by the gases in the [[atmosphere]], giving the Earth a blue [[Halo (optical phenomenon)|halo]] when seen from space.]]
{{Main|Atmosphere of Earth|Climate|Weather}}
The Earth's atmosphere is a key factor in sustaining the [[Nature#Ecosystems|ecosystem]]. The thin layer of gases that envelops the Earth is held in place by gravity. Air is mostly [[nitrogen]], [[oxygen]], [[water vapor]], with much smaller amounts of carbon dioxide, argon, etc. The atmospheric pressure declines steadily with altitude. The [[ozone layer]] plays an important role in depleting the amount of [[ultraviolet]] (UV) radiation that reaches the surface. As [[DNA]] is readily damaged by UV light, this serves to protect life at the surface. The atmosphere also retains heat during the night, thereby reducing the daily temperature extremes.

Terrestrial weather occurs almost exclusively in the [[troposphere|lower part of the atmosphere]], and serves as a convective system for redistributing heat.<ref>{{Cite book|url=https://books.google.com/books?id=AJ4SnHbb-ZcC&pg=PA42|title=Environmental Science: Problems, Connections and Solutions|last1=Miller|last2=Spoolman|first2=Scott|date=September 28, 2007|publisher=Cengage Learning|isbn=978-0-495-38337-6}}</ref> [[Ocean current]]s are another important factor in determining climate, particularly the major underwater [[thermohaline circulation]] which distributes heat energy from the equatorial oceans to the polar regions. These currents help to moderate the differences in temperature between winter and summer in the temperate zones. Also, without the redistributions of heat energy by the ocean currents and atmosphere, the tropics would be much hotter, and the [[polar region]]s much colder.
[[File:Lightnings sequence 2 animation-wcag.gif|thumb|left|[[Lightning]]]]
Weather can have both beneficial and harmful effects. Extremes in weather, such as [[tornado]]es or [[hurricane]]s and [[cyclone]]s, can expend large amounts of energy along their paths, and produce devastation. Surface vegetation has evolved a dependence on the seasonal variation of the weather, and sudden changes lasting only a few years can have a dramatic effect, both on the vegetation and on the animals which depend on its growth for their food.

Climate is a measure of the long-term trends in the weather. Various factors are known to [[Climate variability and change|influence the climate]], including ocean currents, surface [[albedo]], [[greenhouse gas]]es, variations in the solar luminosity, and changes to the Earth's orbit. Based on historical and geological records, the Earth is known to have undergone drastic climate changes in the past, including [[ice age]]s.
[[File:Dszpics1.jpg|thumb|A tornado in central [[Oklahoma]]]]
The climate of a region depends on a number of factors, especially [[latitude]]. A latitudinal band of the surface with similar climatic attributes forms a climate region. There are a number of such regions, ranging from the [[tropical climate]] at the equator to the [[polar climate]] in the northern and southern extremes. Weather is also influenced by the seasons, which result from the [[Earth]]'s [[axis of rotation|axis]] being [[axial tilt|tilted]] relative to its [[orbital plane (astronomy)|orbital plane]]. Thus, at any given time during the summer or winter, one part of the Earth is more directly exposed to the rays of the [[sun]]. This exposure alternates as the Earth revolves in its orbit. At any given time, regardless of season, the [[Northern Hemisphere|Northern]] and [[Southern Hemisphere|Southern]] Hemispheres experience opposite seasons.

Weather is a [[Chaos theory|chaotic system]] that is readily modified by small changes to the [[Natural environment|environment]], so accurate [[Meteorology|weather forecasting]] is limited to only a few days.<ref>{{Cite journal|last1=Stern|first1=Harvey|last2=Davidson|first2=Noel|date=May 25, 2015|title=Trends in the skill of weather prediction at lead times of 1–14 days|journal=Quarterly Journal of the Royal Meteorological Society|volume=141|issue=692|pages=2726–2736|doi=10.1002/qj.2559|bibcode=2015QJRMS.141.2726S|s2cid=119942734|doi-access=free}}</ref> Overall, two things are happening worldwide: (1) temperature is increasing on the average; and (2) regional climates have been undergoing noticeable changes.<ref>{{cite web|title=Tropical Ocean Warming Drives Recent Northern Hemisphere Climate Change|website=Science Daily|date=April 6, 2001|url=https://www.sciencedaily.com/releases/2001/04/010406073554.htm|access-date=May 24, 2006|archive-url=https://web.archive.org/web/20060421222313/http://www.sciencedaily.com/releases/2001/04/010406073554.htm|archive-date=April 21, 2006|url-status=live|df=mdy-all}}</ref>

==Water on the Earth==
[[File:44 - Iguazu - Décembre 2007.jpg|thumb|upright=1.4|The [[Iguazu Falls]] on the border between [[Brazil]] and [[Argentina]]]]
{{Main|Water}}
'''Water''' is a [[chemical substance]] that is composed of [[hydrogen]] and [[oxygen]] (H2O) and is vital for all known forms of life.<ref>{{cite web |url=https://www.un.org/waterforlifedecade/background.html |title=Water for Life |publisher=Un.org |date=March 22, 2005 |access-date=May 14, 2011 |archive-url=https://web.archive.org/web/20110514200432/http://www.un.org/waterforlifedecade/background.html |archive-date=May 14, 2011 |url-status=live |df=mdy-all }}</ref> In typical usage, ''water'' refers only to its liquid form or [[States of matter|state]], but the substance also has a solid state, [[ice]], and a [[gas]]eous state, [[water vapor]], or [[steam]]. <!--About 1.460 [[Tonne#Multiples|petatonnes]]&nbsp;(Pt) (10<sup>21</sup>&nbsp;kilograms) of water-->Water covers 71% of the [[Earth]]'s surface.<ref>{{cite web|url=https://www.cia.gov/the-world-factbook/countries/world/|title=World|work=CIA – World Fact Book|access-date=December 20, 2008|df=mdy-all}}</ref> On Earth, it is found mostly in oceans and other large bodies of water, with 1.6% of water below ground in [[aquifer]]s and 0.001% in the [[atmosphere|air]] as [[vapor]], clouds, and [[precipitation (meteorology)|precipitation]].<ref>[https://web.archive.org/web/20070320034158/http://www.agu.org/sci_soc/mockler.html Water Vapor in the Climate System], Special Report, American Geophysical Union, December 1995.</ref><ref>[https://web.archive.org/web/20080220070111/http://www.unep.org/dewa/assessments/ecosystems/water/vitalwater/ Vital Water]. [[UNEP]].</ref> Oceans hold 97% of surface water, [[glacier]]s, and polar [[ice cap]]s 2.4%, and other land surface water such as rivers, lakes, and ponds 0.6%. Additionally, a minute amount of the Earth's water is contained within biological bodies and manufactured products.

===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]].

===Lakes===
[[File:Lake mapourika NZ.jpeg|thumb|[[Lake Mapourika]], New Zealand]]
{{Main|Lake}}
A lake (from Latin word ''lacus'') is a [[terrain feature]] (or [[physical feature]]), a body of liquid on the surface of a world that is localized to the bottom of [[Depression (geology)|basin]] (another type of landform or terrain feature; that is, it is not global) and moves slowly if it moves at all. On Earth, a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond, and is fed by a river.<ref>
{{cite web
|url=https://www.britannica.com/EBchecked/topic/328083/lake
|author=Britannica Online
|access-date=June 25, 2008
|title=Lake (physical feature)
|quote=[a Lake is] any relatively large body of slowly moving or standing water that occupies an inland basin of appreciable size. Definitions that precisely distinguish lakes, ponds, swamps, and even rivers and other bodies of nonoceanic water are not well established. It may be said, however, that rivers and streams are relatively fast moving; marshes and swamps contain relatively large quantities of grasses, trees, or shrubs; and ponds are relatively small in comparison to lakes. Geologically defined, lakes are temporary bodies of water.
|archive-url=https://web.archive.org/web/20080611194244/https://www.britannica.com/EBchecked/topic/328083/lake
|archive-date=June 11, 2008
|url-status=live
|df=mdy-all
}}
</ref><ref>{{cite web|title=Lake Definition|url=http://www.dictionary.com/browse/lake|website=Dictionary.com|access-date=September 6, 2016|archive-url=https://web.archive.org/web/20160905184816/http://www.dictionary.com/browse/lake|archive-date=September 5, 2016|url-status=live|df=mdy-all}}</ref> The only world other than Earth known to harbor lakes is [[Titan (moon)|Titan]], Saturn's largest moon, which has lakes of [[ethane]], most likely mixed with [[methane]]. It is not known if Titan's lakes are fed by rivers, though Titan's surface is carved by numerous river beds. Natural lakes on Earth are generally found in mountainous areas, [[rift zone]]s, and areas with ongoing or recent [[glacier|glaciation]]. Other lakes are found in [[endorheic basin]]s or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the [[Last Glacial Period|last ice age]]. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them.

====Ponds====
[[File:Mill Pond Sunset.jpg|thumb|The Westborough Reservoir (Mill Pond) in [[Westborough, Massachusetts]]]]
{{Main|Pond}}
A '''pond''' is a [[body of water|body]] of [[Water stagnation|standing water]], either natural or human-made, that is usually smaller than a lake. A wide variety of human-made bodies of water are classified as ponds, including [[water garden]]s designed for aesthetic ornamentation, [[fish pond]]s designed for commercial fish breeding, and [[solar pond]]s designed to store thermal energy. Ponds and lakes are distinguished from streams via [[current (stream)|current]] speed. While currents in streams are easily observed, ponds and lakes possess thermally driven micro-currents and moderate wind driven currents. These features distinguish a pond from many other aquatic terrain features, such as [[stream pool]]s and [[tide pool]]s.

===Rivers===
[[File:View from Cairo Tower 31march2007.jpg|thumb|left|The [[Nile]] river in [[Cairo]], Egypt's capital city]]
{{Main|River}}
A river is a natural [[watercourse]],<ref>[http://www.merriam-webster.com/dictionary/river River {definition}] {{Webarchive|url=https://web.archive.org/web/20100221200545/http://www.merriam-webster.com/dictionary/river |date=February 21, 2010 }} from Merriam-Webster. Accessed February 2010.</ref> usually [[freshwater]], flowing towards an ocean, a lake, a sea or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, and rill; there is no general rule that defines what can be called a river. Many names for small rivers are specific to geographic location; one example is ''Burn'' in Scotland and North-east England. Sometimes a river is said to be larger than a creek, but this is not always the case, due to vagueness in the language.<ref>[http://geonames.usgs.gov/domestic/faqs.htm USGS – U.S. Geological Survey – FAQs] {{Webarchive|url=https://web.archive.org/web/20150701155523/http://geonames.usgs.gov/domestic/faqs.htm |date=July 1, 2015 }}, No. 17 What is the difference between mountain, hill, and [[Summit (topography)|peak]]; lake and pond; or river and [[stream|creek]]?</ref> A river is part of the [[hydrological cycle]]. Water within a river is generally collected from [[Precipitation (meteorology)|precipitation]] through [[surface runoff]], [[groundwater]] recharge, [[Spring (hydrology)|springs]], and the release of stored water in natural ice and snowpacks (i.e., from [[glacier]]s).

===Streams===
[[File:Hawaii Creek.jpg|thumb|A rocky stream in [[Hawaii]]]]
{{Main|Stream}}
A stream is a flowing body of water with a [[Current (stream)|current]], confined within a [[stream bed|bed]] and [[stream bank]]s. In the United States, a stream is classified as a watercourse less than {{convert|60|ft|m|abbr=off}} wide. Streams are important as conduits in the [[water cycle]], instruments in [[groundwater recharge]], and they serve as corridors for fish and [[wildlife]] migration. The biological [[habitat]] in the immediate vicinity of a stream is called a [[riparian zone]]. Given the status of the ongoing [[Holocene extinction]], streams play an important [[wildlife corridor|corridor]] role in connecting [[Habitat fragmentation|fragmented habitats]] and thus in conserving [[biodiversity]]. The study of streams and waterways in general involves many branches of inter-disciplinary natural science and engineering, including [[hydrology]], [[geomorphology|fluvial geomorphology]], [[aquatic ecology]], [[Freshwater fish|fish biology]], [[riparian|riparian ecology]], and others.

==Ecosystems==<!-- This section is linked from Nature -->
[[File:View of loch lomond.JPG|thumb|left|[[Loch Lomond]] in Scotland forms a relatively isolated ecosystem. The fish community of this lake has remained unchanged over a very long period of time.<ref>{{cite journal|last=Adams|first=C.E.|title=The fish community of Loch Lomond, Scotland: its history and rapidly changing status|journal=Hydrobiologia|date=1994|volume=290|issue=1–3|pages=91–102|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=3302548|doi=10.1007/BF00008956|s2cid=6894397|access-date=January 5, 2007|archive-url=https://web.archive.org/web/20120114115347/http://cat.inist.fr/?aModele=afficheN&cpsidt=3302548|archive-date=January 14, 2012|url-status=live|df=mdy-all|doi-access=free}}</ref>]]
[[File:Aravalli.jpg|thumb|left|Lush green [[Aravalli Range|Aravalli Mountain Range]] in the Desert country – [[Rajasthan]], India.]]
[[File:Chicago Downtown Aerial View.jpg|thumb|An aerial view of a [[human ecosystem]]. Pictured is the city of Chicago.]]
{{Main|Ecology|Ecosystem}}
Ecosystems are composed of a variety of [[biotic component|biotic]] and [[abiotic component]]s that function in an interrelated way.<ref>{{cite web |last=Pidwirny |first=Michael |date=2006 |work=Fundamentals of Physical Geography (2nd Edition) |title=Introduction to the Biosphere: Introduction to the Ecosystem Concept |url=http://www.physicalgeography.net/fundamentals/9j.html |access-date=September 28, 2006 |archive-url=https://web.archive.org/web/20110718040429/http://www.physicalgeography.net/fundamentals/9j.html |archive-date=July 18, 2011 |url-status=live |df=mdy-all }}</ref> The structure and composition is determined by various environmental factors that are interrelated. Variations of these factors will initiate dynamic modifications to the ecosystem. Some of the more important components are [[soil]], [[atmosphere]], radiation from the [[sun]], water, and living organisms.
[[File:PenasBlancas, part of the Bosawas Reserve, Jinotega Department, Nicaragua.jpg|thumb|left|Peñas Blancas, part of the [[Bosawás Biosphere Reserve]]. Located northeast of the city of [[Jinotega]] in Northeastern Nicaragua]]
Central to the ecosystem concept is the idea that [[living organism]]s interact with every other element in their local [[environment (biophysical)|environment]]. Eugene Odum, a founder of ecology, stated: "Any unit that includes all of the organisms (ie: the "community") in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e.: exchange of materials between living and nonliving parts) within the system is an ecosystem."<ref name="Odum1971">Odum, EP (1971) ''Fundamentals of ecology'', 3rd edition, Saunders New York</ref> Within the ecosystem, species are connected and dependent upon one another in the [[food chain]], and exchange energy and [[matter]] between themselves as well as with their environment.<ref>{{cite web |last=Pidwirny |first=Michael |date=2006 |work=Fundamentals of Physical Geography (2nd edition) |title=Introduction to the Biosphere: Organization of Life |url=http://www.physicalgeography.net/fundamentals/9d.html |access-date=September 28, 2006 |archive-url=https://web.archive.org/web/20110813100946/http://www.physicalgeography.net/fundamentals/9d.html |archive-date=August 13, 2011 |url-status=live |df=mdy-all }}</ref> The human ecosystem concept is based on the human/nature [[dichotomy]] and the idea that all species are ecologically dependent on each other, as well as with the abiotic constituents of their [[biotope]].<ref>{{Cite book|url=https://books.google.com/books?id=-s5oRDUuMSIC&pg=PA237|title=Biotechnology Fundamentals|last=Khan|first=Firdos Alam|date=2011|publisher=CRC Press|isbn=978-1-4398-2009-4}}</ref>

A smaller unit of size is called a [[microecosystem]]. For example, a microsystem can be a stone and all the life under it. A ''macroecosystem'' might involve a whole [[ecoregion]], with its [[drainage basin]].<ref>{{cite journal|last=Bailey |first=Robert G. |date=April 2004 |title=Identifying Ecoregion Boundaries |journal=Environmental Management |volume=34 |pmid=15883869 |issue=Supplement 1 |url=http://www.fs.fed.us/institute/news_info/Identifying_ecoregion_boundaries.pdf |doi=10.1007/s00267-003-0163-6 |pages=S14–S26 |s2cid=31998098 |url-status=dead |archive-url=https://web.archive.org/web/20091001013622/http://www.fs.fed.us/institute/news_info/Identifying_ecoregion_boundaries.pdf |archive-date=October 1, 2009 }}</ref>

===Wilderness===
[[File:Biogradska suma.jpg|thumb|[[Old-growth forest|Old growth]] [[European Beech]] forest in [[Biogradska Gora]] National Park, [[Montenegro]]]]
{{Main|Wilderness}}
'''Wilderness''' is generally defined as areas that have not been significantly modified by human activity. Wilderness areas can be found in preserves, estates, farms, conservation preserves, ranches, [[:Category:national forests|national forests]], [[national park]]s, and even in urban areas along rivers, gulches, or otherwise undeveloped areas. Wilderness areas and protected [[parks]] are considered important for the survival of certain [[species]], ecological studies, [[Habitat conservation|conservation]], and solitude. Some nature writers believe wilderness areas are vital for the human spirit and creativity,<ref name="Man p155-157">Botkin, Daniel B. (2000) ''No Man's Garden'', Island Press, pp. 155–157, {{ISBN|1-55963-465-0}}.</ref> and some ecologists consider wilderness areas to be an integral part of the Earth's self-sustaining natural [[ecosystem]] (the [[biosphere]]). They may also preserve historic [[genetics|genetic]] traits and that they provide [[habitat]] for wild [[flora (plants)|flora]] and [[fauna (animals)|fauna]] that may be difficult or impossible to recreate in [[zoo]]s, [[arboretum]]s, or [[laboratory|laboratories]].

==Life==
{{Life timeline}}
[[File:Malards in Golden Gate Park.jpg|thumb|left|upright|Female mallard and ducklings – [[reproduction]] is essential for continuing life.]]
{{Main|Life|Biology|Biosphere}}
Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by [[Organism|organization]], [[metabolism]], [[cell growth|growth]], [[adaptation]], response to [[stimulus (physiology)|stimuli]], and [[reproduction]].<ref>{{cite web|date=2006 |url=http://www.calacademy.org/exhibits/xtremelife/what_is_life.php |title=Definition of Life |publisher=California Academy of Sciences |access-date=January 7, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070208220940/http://www.calacademy.org/exhibits/xtremelife/what_is_life.php |archive-date=February 8, 2007 }}</ref> Life may also be said to be simply the characteristic state of [[organism]]s.

Properties common to terrestrial organisms (plants, animals, [[Fungus|fungi]], [[protist]]s, [[archaea]], and bacteria) are that they are cellular, carbon-and-water-based with complex organization, having a metabolism, a capacity to grow, respond to stimuli, and reproduce. An entity with these properties is generally considered life. However, not every definition of life considers all of these properties to be essential. Human-made [[Artificial life|analogs of life]] may also be considered to be life.

The [[biosphere]] is the part of Earth's outer shell—including land, surface rocks, water, air and the atmosphere—within which life occurs, and which [[Biology|biotic]] processes in turn alter or transform. From the broadest [[Geophysiology|geophysiological]] point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the [[lithosphere]] (rocks), [[hydrosphere]] (water), and [[atmosphere]] (air). The entire Earth contains over 75&nbsp;billion tons (150 ''trillion'' pounds or about 6.8×10<sup>13</sup>&nbsp;kilograms) of [[biomass (ecology)|biomass]] (life), which lives within various environments within the biosphere.<ref>The figure "about one-half of one percent" takes into account the following (See, e.g., {{cite book |last=Leckie |first=Stephen |date=1999 |chapter=How Meat-centred Eating Patterns Affect Food Security and the Environment |chapter-url=http://www.idrc.ca/en/ev-30610-201-1-DO_TOPIC.html |title=For hunger-proof cities: sustainable urban food systems |publisher=International Development Research Centre |location=Ottawa |isbn=978-0-88936-882-8 |archive-url=https://web.archive.org/web/20101113020336/http://www.idrc.ca/en/ev-30610-201-1-DO_TOPIC.html |archive-date=November 13, 2010 }}, which takes global average weight as 60&nbsp;kg.), the total human biomass is the average weight multiplied by the current human population of approximately 6.5&nbsp;billion (see, ''e.g.'', {{cite web |title=World Population Information |url=https://www.census.gov/ipc/www/world.html |access-date=September 28, 2006 |publisher=U.S. Census Bureau }}{{Dead link|date=February 2019 |bot=InternetArchiveBot |fix-attempted=yes }}): Assuming 60–70&nbsp;kg to be the average human mass (approximately 130–150&nbsp;[[pound (mass)|lb]] on the average), an approximation of total global human mass of between 390&nbsp;billion (390×10<sup>9</sup>) and 455&nbsp;billion kg (between 845&nbsp;billion and 975&nbsp;billion lb, or about 423&nbsp;million–488&nbsp;million [[short ton]]s). The total biomass of all kinds on earth is estimated to be in excess of 6.8&nbsp;x&nbsp;10<sup>13</sup>&nbsp;kg (75&nbsp;billion short tons). By these calculations, the portion of total biomass accounted for by humans would be very roughly 0.6%.</ref>

Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence.<ref>{{cite web |first=Peter V. |last=Sengbusch |title=The Flow of Energy in Ecosystems – Productivity, Food Chain, and Trophic Level |work=Botany online |publisher=University of Hamburg Department of Biology |url=http://www.biologie.uni-hamburg.de/b-online/e54/54c.htm |access-date=September 23, 2006 |archive-url=https://web.archive.org/web/20110726071651/http://www.biologie.uni-hamburg.de/b-online/e54/54c.htm |archive-date=July 26, 2011 |url-status=live |df=mdy-all }}</ref> More than 2 million species of plant and animal life have been identified to date,<ref>{{cite web |last=Pidwirny |first=Michael |date=2006 |work=Fundamentals of Physical Geography (2nd Edition) |title=Introduction to the Biosphere: Species Diversity and Biodiversity |url=http://www.physicalgeography.net/fundamentals/9h.html |access-date=September 23, 2006 |archive-url=https://web.archive.org/web/20110718040705/http://www.physicalgeography.net/fundamentals/9h.html |archive-date=July 18, 2011 |url-status=live |df=mdy-all }}</ref> and estimates of the actual number of existing species range from several million to well over 50&nbsp;million.<ref>{{cite web |url=http://faculty.plattsburgh.edu/thomas.wolosz/howmanysp.htm |title=How Many Species are There? |work=Extinction Web Page Class Notes |access-date=September 23, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060909194319/http://faculty.plattsburgh.edu/thomas.wolosz/howmanysp.htm |archive-date=September 9, 2006  }}</ref><ref>"Animal." World Book Encyclopedia. 16 vols. Chicago: World Book, 2003. This source gives an estimate of from 2 to 50&nbsp;million.</ref><ref>{{cite web |url=https://www.sciencedaily.com/releases/2003/05/030526103731.htm |title=Just How Many Species Are There, Anyway? |website=Science Daily |date=May 2003 |access-date=September 26, 2006 |archive-url=https://web.archive.org/web/20070211001529/http://www.sciencedaily.com/releases/2003/05/030526103731.htm |archive-date=February 11, 2007 |url-status=live |df=mdy-all }}</ref> The number of individual species of life is constantly in some degree of flux, with new species appearing and others ceasing to exist on a continual basis.<ref>{{cite web |last=Withers |first=Mark A. |display-authors=etal |title=Changing Patterns in the Number of Species in North American Floras |work=Land Use History of North America |url=http://biology.usgs.gov/luhna/chap4.html |date=1998 |access-date=September 26, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060923054200/http://biology.usgs.gov/luhna/chap4.html |archive-date=September 23, 2006  }} Website based on the contents of the book: {{cite book |editor=Sisk, T.D. |date=1998 |title=Perspectives on the land use history of North America: a context for understanding our changing environment |publisher=U.S. Geological Survey, Biological Resources Division |id=USGS/BRD/BSR-1998-0003 |edition=Revised September 1999}}</ref><ref>{{cite web |title=Tropical Scientists Find Fewer Species Than Expected |url=https://www.sciencedaily.com/releases/2002/04/020425072847.htm |date=April 2002 |website=Science Daily |access-date=September 27, 2006 |archive-url=https://web.archive.org/web/20060830182612/http://www.sciencedaily.com/releases/2002/04/020425072847.htm |archive-date=August 30, 2006 |url-status=live |df=mdy-all }}</ref> The total number of species is in rapid decline.<ref>{{cite journal |last=Bunker |first=Daniel E. |display-authors=etal |title=Species Loss and Aboveground Carbon Storage in a Tropical Forest |journal=Science |date=November 2005 |volume=310 |issue=5750 |pages=1029–1031 |doi=10.1126/science.1117682 |pmid=16239439 |bibcode = 2005Sci...310.1029B|citeseerx=10.1.1.465.7559 |s2cid=42696030 }}</ref><ref>{{cite journal |last=Wilcox |first=Bruce A. |title=Amphibian Decline: More Support for Biocomplexity as a Research Paradigm |journal=EcoHealth |date=2006 |volume=3 |issue=1 |doi=10.1007/s10393-005-0013-5|pages = 1–2|s2cid=23011961 }}</ref><ref>{{cite book |editor=Clarke, Robin |editor2=Robert Lamb |editor3=Dilys Roe Ward |date=2002 |title=Global environment outlook 3: past, present and future perspectives |chapter=Decline and loss of species |chapter-url=http://www.unep.org/geo/assessments/global-assessments/global-environment-outlook-3 |publisher=Nairobi, Kenya: UNEP |location=London; Sterling, VA |isbn=978-92-807-2087-7 |url-access=registration |url=https://archive.org/details/globalenvironmen0000unse_z8s0 }}</ref>

===Evolution===
[[File:Amazon Manaus forest.jpg|thumb|An area of the [[Amazon Rainforest]] shared between [[Colombia]] and [[Brazil]]. The [[tropical rainforest]]s of South America contain the largest [[biodiversity|diversity]] of species on [[Earth]].<ref>{{cite web|url=http://earthobservatory.nasa.gov/Newsroom/view.php?id=28907 |title=Why the Amazon Rainforest is So Rich in Species: News |publisher=Earthobservatory.nasa.gov |date=December 5, 2005 |access-date=May 14, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110225204348/http://earthobservatory.nasa.gov/Newsroom/view.php?id=28907 |archive-date=February 25, 2011 }}</ref><ref>{{cite web|url=http://earthobservatory.nasa.gov/Newsroom/view.php?id=28907 |title=Why The Amazon Rainforest Is So Rich in Species |publisher=Sciencedaily.com |date=December 5, 2005 |access-date=May 14, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110225204348/http://earthobservatory.nasa.gov/Newsroom/view.php?id=28907 |archive-date=February 25, 2011 }}</ref>]]
{{Main|Evolution}}
The [[origin of life]] on Earth is not well understood, but it is known to have occurred at least 3.5&nbsp;billion years ago,<ref name="Origin1">{{cite journal|last1=Schopf|first1=J. William|last2=Kudryavtsev|first2=Anatoliy B.|last3=Czaja|first3=Andrew D.|last4=Tripathi|first4=Abhishek B.|title=Evidence of Archean life: Stromatolites and microfossils|journal=Precambrian Research|volume=158|issue=3–4|year=2007|pages=141–155|doi=10.1016/j.precamres.2007.04.009|bibcode=2007PreR..158..141S}}</ref><ref name="Origin2">{{cite journal | last1 = Schopf | first1 = JW | year = 2006 | title = Fossil evidence of Archaean life | doi = 10.1098/rstb.2006.1834 | journal = Philos Trans R Soc Lond B Biol Sci | volume = 361 | issue = 1470| pages = 869–885 | pmid=16754604 | pmc=1578735}}</ref><ref name="RavenJohnson2002">{{cite book|author1=Raven, Peter Hamilton |author2=Johnson, George Brooks |title=Biology|url=https://archive.org/details/biologyrave00rave|url-access=registration|access-date=July 7, 2013|date=2002|publisher=McGraw-Hill Education|isbn=978-0-07-112261-0|page=[https://archive.org/details/biologyrave00rave/page/68 68]|df=mdy-all}}</ref> during the [[hadean]] or [[archean]] eons on a [[Early Earth|primordial Earth]] that had a substantially different environment than is found at present.<ref name=Line>{{cite journal|author = Line, M.|title = The enigma of the origin of life and its timing|journal = Microbiology|volume = 148|issue = Pt 1|pages = 21–27|date=January 1, 2002| pmid = 11782495 | doi = 10.1099/00221287-148-1-21 |doi-access = free}}</ref> These life forms possessed the basic traits of self-replication and inheritable traits. Once life had appeared, the process of [[evolution]] by [[natural selection]] resulted in the development of ever-more diverse life forms.

Species that were unable to adapt to the changing environment and competition from other life forms became extinct. However, the [[fossil]] record retains evidence of many of these older species. Current fossil and [[DNA]] evidence shows that all existing species can trace a continual ancestry back to the first primitive life forms.<ref name=Line/>

When basic forms of plant life developed the process of [[photosynthesis]] the sun's energy could be harvested to create conditions which allowed for more complex life forms.<ref>{{Cite web|url=https://phys.org/news/2016-03-photosynthesis-ancient-thought.html|title=Photosynthesis more ancient than thought, and most living things could do it|website=Phys.org|access-date=2019-01-19|archive-url=https://web.archive.org/web/20190120043127/https://phys.org/news/2016-03-photosynthesis-ancient-thought.html|archive-date=January 20, 2019|url-status=live|df=mdy-all}}</ref> The resultant [[oxygen]] accumulated in the atmosphere and gave rise to the [[ozone layer]]. The incorporation of smaller cells within larger ones resulted in the [[endosymbiotic theory|development of yet more complex cells]] called [[eukaryotes]].<ref>{{cite journal |first=L. V. |last=Berkner |author2=L. C. Marshall |date=May 1965 |title=On the Origin and Rise of Oxygen Concentration in the Earth's Atmosphere |journal=Journal of the Atmospheric Sciences |volume=22 |issue=3 |pages=225–261|doi=10.1175/1520-0469(1965)022<0225:OTOARO>2.0.CO;2 |bibcode=1965JAtS...22..225B |doi-access=free }}</ref> Cells within colonies became increasingly specialized, resulting in true multicellular organisms. With the ozone layer absorbing harmful [[ultraviolet radiation]], life colonized the surface of Earth.

===Microbes===
[[File:Yellow mite (Tydeidae) Lorryia formosa 2 edit.jpg|thumb|upright|A microscopic mite [[Mite|''Lorryia formosa'']]]]
{{Main|Microbe}}
The first form of life to develop on the Earth were microbes, and they remained the only form of life until about a billion years ago when multi-cellular organisms began to appear.<ref>{{cite journal |
author = Schopf J|title = Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic|journal = Proc Natl Acad Sci USA|volume = 91|issue = 15|pages = 6735–42|date = 1994|pmid = 8041691|doi = 10.1073/pnas.91.15.6735 |
pmc = 44277
|bibcode = 1994PNAS...91.6735S|doi-access = free}}</ref> Microorganisms are single-celled organisms that are generally [[microscopic]], and smaller than the human eye can see. They include [[Bacteria]], [[Fungus|Fungi]], [[Archaea]], and [[Protist]]a.

These life forms are found in almost every location on the Earth where there is liquid water, including in the Earth's interior.<ref>{{cite journal|author = Szewzyk U|author2 = Szewzyk R|author3 = Stenström T|title = Thermophilic, anaerobic bacteria isolated from a deep borehole in granite in Sweden|doi= 10.1073/pnas.91.5.1810|journal = Proc Natl Acad Sci USA|volume = 91|issue = 5|pages = 1810–1813|date = 1994|pmid = 11607462|pmc = 43253|bibcode = 1994PNAS...91.1810S|doi-access = free}}</ref>
Their reproduction is both rapid and profuse. The combination of a high mutation rate and a [[horizontal gene transfer]]<ref>{{cite journal|author = Wolska K|title = Horizontal DNA transfer between bacteria in the environment|journal = Acta Microbiol Pol|volume = 52|issue = 3|pages = 233–243|date = 2003|pmid = 14743976}}</ref> ability makes them highly adaptable, and able to survive in new environments, including [[outer space]].<ref>{{cite journal|author = Horneck G|title = Survival of microorganisms in space: a review|journal = Adv Space Res|volume = 1|issue = 14|pages = 39–48|date = 1981|pmid = 11541716|doi = 10.1016/0273-1177(81)90241-6}}</ref> They form an essential part of the planetary ecosystem. However, some microorganisms are [[pathogen]]ic and can post health risk to other organisms.

===Plants and animals===
{{Main|Plant|Animal}}
[[File:Diversity of plants (Streptophyta) version 2.png|thumb|left|A selection of diverse [[plant species]]]]
[[File:Animal diversity.png|thumb|A selection of diverse [[animal species]]]]
Originally [[Aristotle]] divided all living things between plants, which generally do not move fast enough for humans to notice, and animals. In [[Carl Linnaeus|Linnaeus]]' system, these became the [[kingdom (biology)|kingdoms]] [[Vegetabilia]] (later [[Plant]]ae) and [[Animal]]ia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the [[fungus|fungi]] and several groups of [[alga]]e were removed to new kingdoms. However, these are still often considered plants in many contexts. Bacterial life is sometimes included in flora,<ref>{{cite web |title=flora |url=http://webster.com/cgi-bin/dictionary?va=flora |work=Merriam-Webster Online Dictionary |publisher=Merriam-Webster |access-date=September 27, 2006 |archive-url=https://web.archive.org/web/20060430072626/http://webster.com/cgi-bin/dictionary?va=flora |archive-date=April 30, 2006 |url-status=dead |df=mdy-all }}</ref><ref>{{cite book |date=1998 |title=Status and Trends of the Nation's Biological Resources |chapter=Glossary |chapter-url=http://biology.usgs.gov/s+t/SNT/noframe/zy198.htm |publisher=Department of the Interior, Geological Survey |location=Reston, VA |id=SuDocs No. I 19.202:ST 1/V.1-2 |url-status=dead |archive-url=https://web.archive.org/web/20070715060359/http://biology.usgs.gov/s+t/SNT/noframe/zy198.htm |archive-date=July 15, 2007  }}</ref> and some classifications use the term ''bacterial flora'' separately from ''plant flora''.

Among the many ways of classifying plants are by regional [[flora]]s, which, depending on the purpose of study, can also include ''fossil flora'', remnants<br /> of plant life from a previous era. People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and [[terrain]].

Regional floras commonly are divided into categories such as ''native flora'' and ''agricultural and garden flora'', the lastly mentioned of which are intentionally grown and cultivated. Some types of "native flora" actually have been introduced centuries ago by people migrating from one region or continent to another, and become an integral part of the native, or natural flora of the place to which they were introduced. This is an example of how human interaction with nature can blur the boundary of what is considered nature.

Another category of plant has historically been carved out for ''weeds''. Though the term has fallen into disfavor among [[Botany|botanists]] as a formal way to categorize "useless" plants, the informal use of the word "weeds" to describe those plants that are deemed worthy of elimination is illustrative of the general tendency of people and societies to seek to alter or shape the course of nature. Similarly, animals are often categorized in ways such as ''domestic'', ''farm animals'', ''wild animals'', ''pests'', etc. according to their relationship to human life.

Animals as a category have several characteristics that generally set them apart from other living things. Animals are [[eukaryote|eukaryotic]] and usually [[multicellular]] (although see [[Myxozoa]]), which separates them from bacteria, [[archaea]], and most [[protist]]s. They are [[heterotroph]]ic, generally digesting food in an internal chamber, which separates them from plants and [[alga]]e. They are also distinguished from plants, algae, and [[fungus|fungi]] by lacking [[cell wall]]s.

With a few exceptions—most notably the two [[Phylum|phyla]] consisting of [[sponge]]s and [[placozoa]]ns—animals have bodies that are differentiated into [[biological tissue|tissues]]. These include [[muscle]]s, which are able to contract and control locomotion, and a [[nervous system]], which sends and processes signals. There is also typically an internal [[digestion|digestive]] chamber. The eukaryotic cells possessed by all animals are surrounded by a characteristic extracellular matrix composed of [[collagen]] and elastic [[glycoprotein]]s. This may be calcified to form structures like [[Animal shell|shells]], [[bone]]s, and [[spicule (sponge)|spicules]], a framework upon which cells can move about and be reorganized during development and maturation, and which supports the complex anatomy required for mobility.

==Human interrelationship==
{{Human timeline}}
[[File:Na Pali Coast - Kauai.jpg|thumb|left|Despite their natural beauty, the secluded valleys along the [[Na Pali Coast]] in Hawaii are heavily modified by introduced [[invasive species]] such as [[She-oak]].]]

===Human impact===
Although [[humans]] comprise only a minuscule proportion of the total living [[Biomass (ecology)|biomass]] on Earth, the [[human impact on the environment|human effect on nature]] is disproportionately large. Because of the extent of human influence, the boundaries between what humans regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is diminishing at an increasingly rapid pace. A 2020 study published in ''[[Nature (journal)|Nature]]'' found that anthropogenic mass (human-made materials) outweighs all living biomass on earth, with [[Plastic pollution|plastic]] alone exceeding the mass of all land and marine animals combined.<ref>{{cite journal |last1=Elhacham|first1=Emily |last2=Ben-Uri |first2=Liad |display-authors=etal. |date=2020|title=Global human-made mass exceeds all living biomass |journal=Nature |volume=588 |issue=7838 |pages=442–444 |doi=10.1038/s41586-020-3010-5|pmid=33299177 |bibcode=2020Natur.588..442E |s2cid=228077506 }}</ref> And according to a 2021 study published in ''Frontiers in Forests and Global Change'', only about 3% of the planet's terrestrial surface is ecologically and [[fauna]]lly intact, with a low human footprint and healthy populations of native animal species.<ref>{{cite news |last=Carrington |first=Damian |date=April 15, 2021 |title=Just 3% of world's ecosystems remain intact, study suggests |url=https://www.theguardian.com/environment/2021/apr/15/just-3-of-worlds-ecosystems-remain-intact-study-suggests |work=The Guardian |location= |access-date=April 16, 2021}}</ref><ref>{{cite journal |last1=Plumptre|first1=Andrew J. |last2=Baisero |first2=Daniele |display-authors=etal. |date=2021 |title=Where Might We Find Ecologically Intact Communities? |url= |journal=Frontiers in Forests and Global Change |volume=4 |issue= |page=626635 |doi=10.3389/ffgc.2021.626635|bibcode=2021FrFGC...4.6635P |doi-access=free |hdl=10261/242175 |hdl-access=free }}</ref> Philip Cafaro, professor of philosophy at the School of Global Environmental Sustainability at [[Colorado State University]], wrote in 2022 that "the cause of global biodiversity loss is clear: other species are being displaced by a rapidly growing human economy."<ref>{{cite journal |last1= Cafaro|first1=Philip|date=2022 |title=Reducing Human Numbers and the Size of our Economies is Necessary to Avoid a Mass Extinction and Share Earth Justly with Other Species|url=https://www.researchgate.net/publication/359182950|journal=Philosophia|volume=50 |issue= 5|pages=2263–2282 |doi=10.1007/s11406-022-00497-w|s2cid=247433264 |access-date=}}</ref>

The development of [[technology]] by the human race has allowed the greater [[exploitation of natural resources]] and has helped to alleviate some of the risk from [[natural hazards]]. In spite of this progress, however, the fate of human [[civilization]] remains closely linked to changes in the environment. There exists a highly complex [[feedback loop]] between the use of advanced technology and changes to the environment that are only slowly becoming understood.<ref>{{cite web|title=Feedback Loops in Global Climate Change Point to a Very Hot 21st Century|website=Science Daily|date=May 22, 2006|url=http://www.lbl.gov/Science-Articles/Archive/ESD-feedback-loops.html|access-date=January 7, 2007|archive-url=https://web.archive.org/web/20061208131415/http://www.lbl.gov/Science-Articles/Archive/ESD-feedback-loops.html|archive-date=December 8, 2006|url-status=live|df=mdy-all}}</ref> Human-made threats to the Earth's natural environment include [[pollution]], [[deforestation]], and disasters such as oil spills. Humans have contributed to the [[Holocene extinction|extinction]] of many plants and animals,<ref>{{Cite book |last=Kolbert |first=Elizabeth |author-link=Elizabeth Kolbert |title=The Sixth Extinction: An Unnatural History |title-link=The Sixth Extinction: An Unnatural History |year=2014 |publisher=[[Henry Holt and Company]] |location=New York City |isbn=978-0805092998}}</ref> with roughly 1 million species threatened with extinction within decades.<ref>{{Cite journal|doi=10.1126/science.aax9287|title=Landmark analysis documents the alarming global decline of nature|last=Stokstad|first=Erik|date=5 May 2019|journal=[[Science (journal)|Science]]|s2cid=166478506}}</ref> The [[biodiversity loss|loss of biodiversity]] and ecosystem functions over the last half century have impacted the extent that nature can contribute to human quality of life,<ref>{{cite journal |last1=Brauman |first1=Kate A. |last2=Garibaldi |first2=Lucas A. |date=2020 |title=Global trends in nature's contributions to people |url= |journal=[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]] |volume=117 |issue=51 |pages=32799–32805 |doi=10.1073/pnas.2010473117|pmid=33288690 |pmc=7768808 |bibcode=2020PNAS..11732799B |doi-access=free }}</ref> and continued declines could pose a major threat to the continued existence of human civilization, unless a rapid course correction is made.<ref>{{cite journal |last1=Bradshaw |first1=Corey J. A. |last2=Ehrlich |first2=Paul R. |last3=Beattie |first3=Andrew |last4=Ceballos |first4=Gerardo |last5=Crist |first5=Eileen |last6=Diamond |first6=Joan |last7=Dirzo |first7=Rodolfo |last8=Ehrlich |first8=Anne H. |last9=Harte |first9=John |last10=Harte |first10=Mary Ellen |last11=Pyke |first11=Graham |last12=Raven |first12=Peter H. |last13=Ripple |first13=William J. |last14=Saltré |first14=Frédérik |last15=Turnbull |first15=Christine |last16=Wackernagel |first16=Mathis |last17=Blumstein |first17=Daniel T. |date=2021 |title=Underestimating the Challenges of Avoiding a Ghastly Future |journal=Frontiers in Conservation Science |volume=1 |issue= |pages= |doi=10.3389/fcosc.2020.615419 |access-date=|doi-access=free }}</ref> The value of natural resources to human society is not reflected in [[market failure|market prices]] because mostly natural resources are available free of charge. This distorts market pricing of natural resources and at the same time leads to underinvestment in our natural assets. The annual global cost of public subsidies that damage nature is conservatively estimated at $4–6 trillion (million million). Institutional protections of these natural goods, such as the oceans and rainforests, are lacking. Governments have not prevented these economic [[externalities]].<ref>UK Government Official Documents, February 2021, [https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/957629/Dasgupta_Review_-_Headline_Messages.pdf "The Economics of Biodiversity: The Dasgupta Review Headline Messages"] p. 2</ref><ref>{{cite news |last=Carrington |first=Damian |date=February 2, 2021 |title=Economics of biodiversity review: what are the recommendations? |url=https://www.theguardian.com/environment/2021/feb/02/economics-of-biodiversity-review-what-are-the-recommendations |work= [[The Guardian]]|location= |access-date=13 November 2021}}</ref>

Humans employ nature for both leisure and economic activities. The acquisition of natural resources for industrial use remains a sizable component of the world's [[economic system]].<ref>{{Cite web|url=https://knoema.com/zscvyje/natural-resources-contribution-to-gdp|title=Natural Resources contribution to GDP|date=November 2014|website=World Development Indicators (WDI)|archive-url=https://web.archive.org/web/20141223080408/https://knoema.com/zscvyje/natural-resources-contribution-to-gdp|archive-date=December 23, 2014|url-status=dead}}</ref><ref>{{cite web|url=https://www.cia.gov/library/publications/the-world-factbook/fields/2012.html|title=GDP – Composition by Sector|publisher=[[Central Intelligence Agency]]|work=[[The World Factbook]]|access-date=February 19, 2017|archive-url=https://web.archive.org/web/20140522215220/https://www.cia.gov/library/publications/the-world-factbook/fields/2012.html|archive-date=May 22, 2014|url-status=dead|df=mdy-all}}</ref> Some activities, such as hunting and fishing, are used for both sustenance and leisure, often by different people. [[Agriculture#History|Agriculture]] was first adopted around the [[9th millennium BCE]]. Ranging from food production to energy, nature influences economic wealth.

Although early humans gathered uncultivated plant materials for food and employed the [[medicinal plant|medicinal properties of vegetation]] for healing,<ref>{{cite web|url = http://www.nps.gov/plants/medicinal/plants.htm|title = Plant Conservation Alliance – Medicinal Plant Working Groups Green Medicine|publisher = US National Park Services|access-date = September 23, 2006|archive-url = https://web.archive.org/web/20061009003035/http://www.nps.gov/plants/medicinal/plants.htm|archive-date = October 9, 2006|url-status=live|df = mdy-all}}</ref> most modern human use of plants is through [[agriculture]]. The [[land conversion|clearance of large tracts]] of land for [[crop]] growth has led to a significant reduction in the amount available of [[forestation]] and [[wetlands]], resulting in the [[loss of habitat]] for many plant and animal species as well as increased [[erosion]].<ref>{{cite web|last = Oosthoek|first = Jan|date = 1999|url = http://www.eh-resources.org/philosophy.html|title = Environmental History: Between Science & Philosophy|publisher = Environmental History Resources|access-date = December 1, 2006|archive-url = https://web.archive.org/web/20070626085227/http://www.eh-resources.org/philosophy.html|archive-date = June 26, 2007|url-status=live|df = mdy-all}}</ref>

===Aesthetics and beauty===
[[File:Cyclamen coum (d.j.b.) 02.jpg|thumb|Aesthetically pleasing flowers]]
Beauty in nature has historically been a prevalent theme in art and books, filling large sections of libraries and bookstores. That nature has been depicted and celebrated by so much art, photography, poetry, and other literature shows the strength with which many people associate nature and beauty. Reasons why this association exists, and what the association consists of, are studied by the branch of philosophy called [[aesthetics]]. Beyond certain basic characteristics that many philosophers agree about to explain what is seen as beautiful, the opinions are virtually endless.<ref>{{cite web|url=http://www.wilderness.org/Library/Documents/Beauty_Quotes.cfm |title=On the Beauty of Nature |publisher=The Wilderness Society |access-date=September 29, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060909220214/http://www.wilderness.org/Library/Documents/Beauty_Quotes.cfm |archive-date=September 9, 2006 }}</ref> Nature and wildness have been important subjects in various eras of world history. An early tradition of [[landscape art]] began in China during the [[Tang Dynasty art|Tang Dynasty]] (618–907). The tradition of representing nature ''as it is'' became one of the aims of [[Chinese painting]] and was a significant influence in Asian art.

Although natural wonders are celebrated in the [[Psalms]] and the [[Book of Job]], [[wilderness]] portrayals in art became more prevalent in the 1800s, especially in the works of the [[Romantic movement]]. [[Kingdom of Great Britain|British]] artists [[John Constable]] and [[J. M. W. Turner]] turned their attention to capturing the beauty of the natural world in their paintings. Before that, paintings had been primarily of religious scenes or of human beings. [[William Wordsworth]]'s poetry described the wonder of the natural world, which had formerly been viewed as a threatening place. Increasingly the valuing of nature became an aspect of Western culture.<ref name=History>[http://www.spacesfornature.org/greatspaces/conservation.html History of Conservation] {{Webarchive|url=https://web.archive.org/web/20060708005819/http://www.spacesfornature.org/greatspaces/conservation.html |date=July 8, 2006 }} BC Spaces for Nature. Accessed: May 20, 2006.</ref> This artistic movement also coincided with the [[Transcendentalism|Transcendentalist movement]] in the Western world. A common classical idea of beautiful art involves the word [[mimesis]], the imitation of nature. Also in the realm of ideas about beauty in nature is that the perfect is implied through perfect mathematical [[Substantial form|forms]] and more generally by [[patterns in nature]]. As David Rothenburg writes, "The beautiful is the root of science and the goal of art, the highest possibility that humanity can ever hope to see".<ref>{{cite book | title=Survival of the Beautiful: Art, Science and Evolution | publisher=Bloomsbury | author=Rothenberg, David | isbn=978-1-60819-216-8 | date=2011 | url-access=registration | url=https://archive.org/details/survivalofbeauti0000roth }}</ref>{{rp|281}}

==Matter and energy==
[[File:Hydrogen Density Plots.png|thumb|The first few [[hydrogen atom]] [[Atomic orbital|electron orbitals]] shown as cross-sections with color-coded probability density]]
{{Main|Matter|Energy}}
Some fields of science see nature as matter in motion, obeying certain laws of nature which science seeks to understand. For this reason the most fundamental science is generally understood to be "[[physics]]"—the name for which is still recognizable as meaning that it is the "''study of nature''".

Matter is commonly defined as the substance of which physical objects are composed. It constitutes the [[observable universe]]. The visible components of the universe are now believed to compose only 4.9 percent of the total mass. The remainder is believed to consist of 26.8 percent [[cold dark matter]] and 68.3 percent [[dark energy]].<ref name="planck_overview">{{cite journal |title=Planck 2013 results. I. Overview of products and scientific results – Table 9. |journal=[[Astronomy and Astrophysics]] |first1=P. A. R. |last1=Ade |first2=N. |last2=Aghanim |author2-link=Nabila Aghanim|first3=C. |last3=Armitage-Caplan |last4=et al. (Planck Collaboration) |date=March 22, 2013 |arxiv=1303.5062|bibcode = 2014A&A...571A...1P |doi=10.1051/0004-6361/201321529 |volume=571 |pages=A1|s2cid=218716838 }}</ref> The exact arrangement of these components is still unknown and is under intensive investigation by physicists.

The behaviour of matter and energy throughout the observable universe appears to follow well-defined [[physical law]]s. These laws have been employed to produce [[Physical cosmology|cosmological]] models that successfully explain the structure and the evolution of the universe we can observe. The mathematical expressions of the laws of physics employ a set of twenty [[physical constant]]s<ref>{{cite web|last = Taylor|first = Barry N.|date = 1971|url = http://www.physics.nist.gov/cuu/Constants/introduction.html|title = Introduction to the constants for nonexperts|publisher = National Institute of Standards and Technology|access-date = January 7, 2007|archive-url = https://web.archive.org/web/20070107012004/http://physics.nist.gov/cuu/Constants/introduction.html|archive-date = January 7, 2007|url-status = dead|df = mdy-all}}</ref> that appear to be static across the observable universe.<ref>{{cite journal|author=Varshalovich, D.A.|author2=Potekhin, A.Y.|author3=Ivanchik, A.V. |name-list-style=amp|title=Testing cosmological variability of fundamental constants|journal=AIP Conference Proceedings|date=2000|volume=506|page=503|arxiv=physics/0004062|doi=10.1063/1.1302777|bibcode=2000AIPC..506..503V|citeseerx=10.1.1.43.6877}}</ref> The values of these constants have been carefully measured, but the reason for their specific values remains a mystery.

==Beyond Earth==
{{Main|Outer space|Universe|Extraterrestrial life}}

[[File:Planets2013.svg|thumb|left|upright=1.3|[[Planet]]s of the [[Solar System]] ''(sizes to scale, distances and illumination not to scale)'']]
[[File:NGC 4414 (NASA-med).jpg|thumb|'''[[NGC 4414]]''' is a spiral galaxy in the constellation [[Coma Berenices]] about 56,000 [[light-year]]s in diameter and approximately 60 million light-years from [[Earth]].]]

Outer space, also simply called ''space'', refers to the relatively empty regions of the [[Universe]] outside the [[atmosphere]]s of celestial bodies. ''Outer'' space is used to distinguish it from [[airspace]] (and terrestrial locations). There is no discrete boundary between [[atmosphere of Earth|Earth's atmosphere]] and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the [[Solar System]] is called [[interplanetary medium|interplanetary space]], which passes over into [[interstellar medium|interstellar space]] at what is known as the [[Heliopause (astronomy)|heliopause]].

Outer space is sparsely filled with several dozen types of [[organic chemistry|organic]] [[molecule]]s discovered to date by [[rotational spectroscopy|microwave spectroscopy]], [[cosmic microwave background|blackbody radiation]] left over from the [[Big Bang]] and the origin of the universe, and [[cosmic ray]]s, which include [[ion]]ized [[atomic nucleus|atomic nuclei]] and various [[subatomic particle]]s. There is also some gas, [[plasma (physics)|plasma]] and [[dust]], and small [[meteor]]s. Additionally, there are signs of human life in outer space today, such as material left over from previous crewed and uncrewed launches which are a potential hazard to spacecraft. Some of this [[space debris|debris]] re-enters the atmosphere periodically.

Although Earth is the only body within the [[Solar System]] known to support life, evidence suggests that in the distant past the planet [[Mars]] possessed bodies of liquid water on the surface.<ref>{{cite journal|author = Bibring, J |display-authors=etal|title = Global mineralogical and aqueous mars history derived from OMEGA/Mars Express data|journal = Science|volume = 312|issue = 5772|pages = 400–404|date = 2006|pmid = 16627738|doi = 10.1126/science.1122659|bibcode = 2006Sci...312..400B|s2cid=13968348 |doi-access = }}</ref> For a brief period in Mars' history, it may have also been capable of forming life. At present though, most of the water remaining on Mars is frozen.
If life exists at all on Mars, it is most likely to be located underground where liquid water can still exist.<ref>{{cite web|first = Tariq|last = Malik|date = March 8, 2005|url = http://www.nbcnews.com/id/7129347|title = Hunt for Mars life should go underground|publisher = Space.com via NBC News|access-date = September 4, 2006|df = mdy-all}}</ref>

Conditions on the other terrestrial planets, [[Mercury (planet)|Mercury]] and [[Venus]], appear to be too harsh to support life as we know it. But it has been conjectured that [[Europa (moon)|Europa]], the fourth-largest moon of [[Jupiter]], may possess a sub-surface ocean of liquid water and could potentially host life.<ref>{{cite web|author = Turner, Scott|date = March 2, 1998|url = http://www2.jpl.nasa.gov/galileo/news8.html|title = Detailed Images From Europa Point To Slush Below Surface|publisher = NASA|access-date = September 28, 2006|archive-url = https://web.archive.org/web/20060929232149/http://www2.jpl.nasa.gov/galileo/news8.html|archive-date = September 29, 2006|url-status = dead|df = mdy-all}}</ref>

Astronomers have started to discover extrasolar [[Earth analog]]s – planets that lie in the [[circumstellar habitable zone|habitable zone]] of space surrounding a [[star]], and therefore could possibly host life as we know it.<ref>Choi, Charles Q. (March 21, 2011) [http://www.space.com/11188-alien-earths-planets-sun-stars.html New Estimate for Alien Earths: 2 Billion in Our Galaxy Alone | Alien Planets, Extraterrestrial Life & Extrasolar Planets | Exoplanets & Kepler Space Telescope] {{Webarchive|url=https://web.archive.org/web/20130703101746/http://www.space.com/11188-alien-earths-planets-sun-stars.html |date=July 3, 2013 }}. Space.com.</ref>

==See also==
{{Portal|Astronomy|Earth sciences|Ecology|Environment|Science|Biology|Animals|Weather|World}}
{{div col|colwidth=20em}}
* [[Force of nature (disambiguation)|Force of nature]]
* [[Human nature]]
* [[Natural history]]
* [[Naturalism (disambiguation)|Naturalism]]
* [[Natural landscape]]
* [[Natural law]]
* [[Natural resource]]
* [[Natural science]]
* [[Natural theology]]
* [[Nature reserve]]
* [[Nature versus nurture]]
* [[Nature worship]]
* [[Naturism]]
* [[Rewilding (conservation biology)|Rewilding]]
{{div col end}}

'''Media:'''
* ''[[National Wildlife (magazine)|National Wildlife]]'', a publication of the National Wildlife Federation
* ''[[Natural History (Pliny)|Natural History]]'', by [[Pliny the Elder]]
* ''[[Natural World (TV series)|Natural World]]'' (TV series)
* ''[[Nature (essay)|Nature]]'', by [[Ralph Waldo Emerson]]
* ''[[Nature (journal)|Nature]]'', a prominent scientific journal
* ''[[Nature (TV series)|Nature]]'' (TV series)
* ''[[The World We Live In (Life magazine)]]''

'''Organizations:'''
* [[Nature Detectives]]
* [[The Nature Conservancy]]

'''Philosophy:'''
* [[Balance of nature]] (biological fallacy), a discredited concept of natural equilibrium in predator–prey dynamics
* [[Mother Nature]]
* [[Naturalism (philosophy)|Naturalism]], any of several philosophical stances, typically those descended from [[materialism]] and [[pragmatism]] that do not distinguish the supernatural from nature;<ref>Papineau, David (2016) [https://plato.stanford.edu/archives/win2016/entries/naturalism/  "Naturalism"], The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.),  {{Webarchive|url=https://web.archive.org/web/20190401175926/https://plato.stanford.edu/archives/win2016/entries/naturalism/ |date=April 1, 2019 }}></ref> this includes the ''methodological naturalism'' of natural science, which makes the [[methodology|methodological]] assumption that [[observation|observable]] events in nature are explained only by natural causes, without assuming either the existence or non-existence of the supernatural
* [[Nature (philosophy)]]

==Notes and references==
{{Reflist}}

== Further reading ==
* {{Cite journal |last1=Droz |first1=Layna |last2=Chen |first2=Hsun-Mei |last3=Chu |first3=Hung-Tao |last4=Fajrini |first4=Rika |last5=Imbong |first5=Jerry |last6=Jannel |first6=Romaric |last7=Komatsubara |first7=Orika |last8=Lagasca-Hiloma |first8=Concordia Marie A. |last9=Meas |first9=Chansatya |last10=Nguyen |first10=Duy Hung |last11=Sherpa |first11=Tshering Ongmu |display-authors=1 |date=May 31, 2022 |title=Exploring the diversity of conceptualizations of nature in East and South-East Asia |journal=Humanities and Social Sciences Communications |volume=9 |issue=1 |pages=1–12 |doi=10.1057/s41599-022-01186-5 |issn=2662-9992 |doi-access=free}}
* {{cite journal |last1=Ducarme |first1=Frédéric |last2=Couvet |first2=Denis |year=2020 |title=What does 'nature' mean? |journal=[[Palgrave Communications]] |volume=6 |issue=14 |publisher=[[Springer Nature]] |doi=10.1057/s41599-020-0390-y |doi-access=free }}
* {{cite book |last1=Emerson |first1=Ralph W. |year=1836 |title=Nature |location=Boston|publisher=James Munroe & Co }}
* Farber, Paul Lawrence (2000), ''Finding Order in Nature: The Naturalist Tradition from Linnaeus to E. O. Wilson''. Johns Hopkins University Press: Baltimore.
* {{cite web |url=https://theconversation.com/have-we-reached-the-end-of-nature-our-relationship-with-the-environment-is-in-crisis-206278|title=Have we reached the end of nature? Our relationship with the environment is in crisis|last=Lynch|first=Derek |date=October 17, 2023|website= [[The Conversation (website)|The Conversation]]|publisher= |access-date= |quote=}}
* {{cite book |last1=Naddaf|first1=Gerard |year=2006 |title=The Greek Concept of Nature|location=Albany|publisher=SUNY Press }}
* {{cite journal |last1=Piccolo|first1=John J. |last2=Taylor|first2=Bron |last3=Washington|first3=Haydn |last4=Kopnina|first4=Helen |last5=Gray|first5=Joe |last6=Alberro|first6=Heather |last7= Orlikowska|first7=Ewa|date=2022 |title="Nature's contributions to people" and peoples' moral obligations to nature|url= |journal=[[Biological Conservation (journal)|Biological Conservation]]|volume=270 |issue= |page=109572 |doi=10.1016/j.biocon.2022.109572|s2cid=248769087 |doi-access=free}}
* {{cite book |last1=Worster |first1=D. |year=1994 |title=Nature's Economy: A History of Ecological Ideas |location=Cambridge  |publisher=[[Cambridge University Press]] }}

==External links==
{{Sister project links}}
* [http://www.iucnredlist.org/ The IUCN Red List of Threatened Species (iucnredlist.org)]
* {{cite web |url=https://www.encyclopedie-environnement.org/en/life/what-is-nature/ |title=What is nature? |last1=Ducarme |first1=Frédéric |date=3 January 2021 |website=Encyclopedia of the Environment |access-date=}}

{{Earth}}
{{Nature}}
{{Natural science}}
{{Environmental science}}
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[[Category:Nature| ]]
[[Category:Environmental science]]
[[Category:Environmental social science concepts]]
[[Category:Main topic articles]]