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'''Nature''', in the broadest sense, is equivalent to the '''natural world''', '''physical universe''', '''material world''' or '''material universe'''. "Nature" refers to the [[phenomenon|phenomena]] of the physical world, and also to [[life]] in general. The term generally does not include manufactured objects and human interaction unless qualified in ways such as, e.g., "[[human nature]]" or "the whole of nature". Nature is also generally distinguished from the [[supernatural]].  It ranges in scale from the [[subatomic]] to the [[galaxy|galactic]].

'''Nature''', in the broadest sense, is equivalent to the ''natural world'', ''physical universe'', ''material world'' or ''material universe''. "Nature" refers to the [[phenomenon|phenomena]] of the physical world, and also to [[life]] in general. The term generally does not include manufactured objects and human interaction unless qualified in ways such as, e.g., "[[human nature]]" or "the whole of nature". Nature is also generally distinguished from the [[supernatural]].  It ranges in scale from the [[subatomic]] to the [[galaxy|galactic]].

==Introduction==

==Etymology==

The word "nature" is derived from the Latin word ''natura'', or "the course of things, natural character."<ref>{{cite web |url=http://www.etymonline.com/index.php?term=nature |title=Nature |work=Online Etymology Dictionary |last=Harper |first=Douglas |accessmonthday=September 23|accessyear=2006}}</ref> ''Natura'' was a Latin translation of the Greek word ''[[physis]]'' (φύσις), which originally related to the intrinsic characteristics that plants, animals, and other features of the world develop of their own accord.<ref>A useful though somewhat erratically presented account of the pre-Socratic use of the concept of φύσις may be found in Naddaf, Gerard ''The Greek Concept of Nature'', SUNY Press, 2006. The word φύσις, while first used in connection with a plant in Homer (as we have seen), occurs very 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> This is shown in the first written use of the word φύσις, in connection with a plant.<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]]'' 10.302-3 (ed. A.T. Murray). (The word is dealt with thoroughly in Liddell and Scott's ''[http://archimedes.fas.harvard.edu/pollux Greek Lexicon]''.) For later but still very early Greek uses of the term, see related below.</ref> The concept of nature as a whole, the physical [[universe]], is one of several expansions of the original notion; it began with certain core applications of the word φύσις by pre-Socratic philosophers, and has steadily gained currency ever since. This usage was confirmed during the advent of modern [[scientific method]] in the last several centuries.<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: {{cite web |url=http://www.etymonline.com/index.php?term=physical |title=Physical |work=Online Etymology Dictionary |last=Harper |first=Douglas |accessmonthday=September 20|accessyear=2006}}</ref>

The word "nature" is derived from the Latin word ''natura'', or "the course of things, natural character."[http://www.etymonline.com/index.php?term=nature] ''Natura'' was a Latin translation of the Greek word ''[[physis]]'' (φύσις), which originally related to the intrinsic characteristics that plants, animals, and other features of the world develop of their own accord. A useful though somewhat erratically presented account of the pre-Socratic use of the concept of φύσις may be found in Naddaf, Gerard ''The Greek Concept of Nature'', SUNY Press, 2006. The word φύσις, while first used in connection with a plant in Homer (as we have seen), occurs very 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). This is shown in the first written use of the word φύσις, in connection with a plant. 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]]'' 10.302-3 (ed. A.T. Murray). (The word is dealt with thoroughly in Liddell and Scott's ''[http://archimedes.fas.harvard.edu/pollux Greek Lexicon]''.) For later but still very early Greek uses of the term, see related below. The concept of nature as a whole, the physical [[universe]], is one of several expansions of the original notion; it began with certain core applications of the word φύσις by pre-Socratic philosophers, and has steadily gained currency ever since. This usage was confirmed during the advent of modern [[scientific method]] in the last several centuries. 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." The etymology of the word "physical" shows its use as a synonym for "natural" in about the mid-15th century: [http://www.etymonline.com/index.php?term=physical]

Within the various uses of the word today, "nature" may refer to the general realm of various types of living plants and animals, and in some cases to the processes associated with inanimate objects &ndash; the way that particular types of things exist and change of their own accord, such as the [[weather]] and [[geology]] of the Earth, and the [[matter]] and [[energy]] of which all these things are composed.  It is often taken to mean the "[[natural environment]]" or [[wilderness]] &ndash; wild animals, rocks, forest, beaches, and in general those things that have not been substantially altered by human intervention, or which persist despite human intervention.  This more traditional concept of natural things which can still be found today implies a distinction between the natural and the [[artificial]], with the latter being understood as that which has been brought into being by a [[human]] or human-like [[consciousness]] or [[mind]].

Within the various uses of the word today, "nature" may refer to the general realm of various types 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, and the [[matter]] and [[energy]] of which all these things are composed.  It is often taken to mean the "[[natural environment]]" or [[wilderness]]; wild animals, rocks, forest, beaches, and in general those things that have not been substantially altered by human intervention, or which persist despite human intervention.  This more traditional concept of natural things which can still be found today implies a distinction between the natural and the [[artificial]], with the latter being understood as that which has been brought into being by a [[human]] or human-like [[consciousness]] or [[mind]].

== Earth ==

== Earth ==

'''Earth''' (or, "the earth") is the fifth largest [[planet]] in the [[solar system]], third in order of distance from the [[Sun]]. It is the largest of its [[planetary system]]'s [[terrestrial planet]]s and the only place in the [[universe]] known to support life.  

'''Earth''' (or, "the earth") is the fifth largest [[planet]] in the [[solar system]], third in order of distance from the [[Sun]]. It is the largest of its [[planetary system]]'s [[terrestrial planet]]s and the only place in the [[universe]] known to support life.  

The most prominent features of the earth's climate are its two large polar regions, two relatively narrow [[temperate]] zones, and a wide [[equator]]ial [[tropical]] to [[subtropical]] region.<ref>An excellent summary description of global climate can be found at: {{cite web |url=http://www.blueplanetbiomes.org/climate.htm |title=World Climates |work=Blue Planet Biomes |accessmonthday=September 21|accessyear=2006}}</ref> [[precipitation (meteorology)|Precipitation]] patterns vary widely according to location, ranging from several [[metre]]s of water per year to less than a [[millimetre]]. About 70 percent of the surface is covered by salt-water oceans. The remainder consists of continents and islands, with the vast majority of the inhabited land in the [[Northern Hemisphere]].  

The most prominent features of the earth's climate are its two large polar regions, two relatively narrow [[temperate]] zones, and a wide [[equator]]ial [[tropical]] to [[subtropical]] region. An excellent summary description of global climate can be found at:[http://www.blueplanetbiomes.org/climate.htm] [[precipitation (meteorology)|Precipitation]] patterns vary widely according to location, ranging from several [[metre]]s of water per year to less than a [[millimetre]]. About 70 percent of the surface is covered by salt-water oceans. The remainder consists of continents and islands, with the vast majority 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 [[tectonic plate]]s that gradually migrate across the surface over geologic time spans, which at least several times have changed relatively quickly. The interior of the planet remains active, with a thick layer of molten [[Earth mantle]] and an iron-filled core that generates a [[magnetic field]].

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 [[tectonic plate]]s that gradually migrate across the surface over geologic time spans, which at least several times have changed relatively quickly. The interior of the planet remains active, with a thick layer of molten [[Earth mantle]] and an iron-filled core that generates a [[magnetic 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 = http://www.sciencedaily.com/releases/2005/09/050911103921.htm | title = Calculations favor reducing atmopshere for early Earth | publisher = Science Daily | accessdate = 2007-01-06 }}</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 | accessdate = 2007-01-07 }}</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, Bernard Walter | date = March, 28 1997  | url = http://vathena.arc.nasa.gov/curric/land/global/climchng.html | title = History of Climate Change | publisher = NASA | accessdate = 2007-01-07 }}</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 | accessdate = 2007-01-07 }}</ref>

The [[atmosphere|atmospheric]] conditions have been significantly altered from the original conditions by the presence of life forms, [http://www.sciencedaily.com/releases/2005/09/050911103921.htm] 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,[http://www.epa.gov/climatechange/science/pastcc.html] 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.[http://vathena.arc.nasa.gov/curric/land/global/climchng.html] [http://www.aip.org/history/climate/]

===Historical perspective===

===Historical perspective===

Based on the available evidence, scientists have reconstructed detailed information about the planet's past. Earth is estimated to have formed approximately 4.55 billion years ago out of the [[solar nebula]], along with the Sun and other planets.<ref>{{cite book |first=G. Brent |last=Dalrymple |year=1991 |title=The Age of the Earth |publisher=Stanford University Press |location=Stanford |id=ISBN 0-8047-1569-6}}</ref> The moon formed relatively soon afterwards (roughly 20 million years later, or 4.53 billion years ago).

Based on the available evidence, scientists have reconstructed detailed information about the planet's past. Earth is estimated to have formed approximately 4.55 billion years ago out of the [[solar nebula]], along with the Sun and other planets. (The Age of the Earth, ISBN 0-8047-1569-6) The moon formed relatively soon afterwards (roughly 20 million years later, or 4.53 billion years ago).

Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgassing and [[Volcano|volcanic]] activity produced the primordial atmosphere. Condensing [[water vapor]], augmented by [[ice]] delivered by [[comet]]s, [[Origin of the world's oceans|produced the oceans]].<ref>{{cite journal |first=A. |last=Morbidelli |coauthors=''et al.'' |year=2000 |url=http://adsabs.harvard.edu/abs/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=pp. 1309-1320}}</ref> The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago.<ref>{{cite news | title=Earth's Oldest Mineral Grains Suggest an Early Start for Life | publisher=NASA Astrobilogy Institute | date=2001-12-24 | url=http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=76 |accessmonthday=May 24|accessyear=2006}}</ref>

Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgassing and [[Volcano|volcanic]] activity produced the primordial atmosphere. Condensing [[water vapor]], augmented by [[ice]] delivered by [[comet]]s, [[Origin of the world's oceans|produced the oceans]].[http://adsabs.harvard.edu/abs/2000M&PS...35.1309M] The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago. [http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=76]

Continents formed, then broke up and re-formed as the surface of Earth reshaped itself over the course of hundreds of millions of years, occasionally combining to make a [[supercontinent]]. Roughly 750 million years ago, the earliest known supercontinent [[Rodinia]], began to break apart. The continents later recombined to form [[Pannotia]] which broke apart about 540 million years ago, then finally [[Pangaea]], which broke apart about 180 million years ago.<ref>{{cite journal |first=J.B. |last=Murphy |coauthors=R.D. Nance |year=2004 |url=http://www.americanscientist.org/template/AssetDetail/assetid/34004;jsessionid=aaa4W2jLnnG9QG |title=How do supercontinents assemble? |journal=American Scientist |volume=92 |issue=4 |id={{doi|10.1511/2004.4.324}} |pages=pp. 324-333}}</ref>

Continents formed, then broke up and re-formed as the surface of Earth reshaped itself over the course of hundreds of millions of years, occasionally combining to make a [[supercontinent]]. Roughly 750 million years ago, the earliest known supercontinent [[Rodinia]], began to break apart. The continents later recombined to form [[Pannotia]] which broke apart about 540 million years ago, then finally [[Pangaea]], which broke apart about 180 million years ago.[http://www.americanscientist.org/template/AssetDetail/assetid/34004]

There is significant evidence, still being discussed among scientists, that a severe [[Glacier|glacial]] action during the [[Neoproterozoic]] era covered much of the planet in a sheet of ice. 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 million years ago.<ref>{{cite book |first=J.L. |last=Kirschvink |year=1992 |chapter=Late Proterozoic Low-Latitude Global Glaciation: The Snowball Earth |chapterurl=http://www.gps.caltech.edu/~jkirschvink/pdfs/firstsnowball.pdf |title=The Proterozoic Biosphere |editor=J.W. Schopf, C. Klein eds. |publisher=Cambridge University Press |location=Cambridge |pages=pp. 51-52 |id=ISBN 0-521-36615-1}}</ref>

There is significant evidence, still being discussed among scientists, that a severe [[Glacier|glacial]] action during the [[Neoproterozoic]] era covered much of the planet in a sheet of ice. 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 million years ago.[http://www.gps.caltech.edu/~jkirschvink/pdfs/firstsnowball.pdf] ISBN 0-521-36615-1

Since the [[Cambrian explosion]] there have been five distinctly identifiable [[Extinction event|mass extinctions]].<ref>{{cite journal |last=Raup |first=David M. |coauthors=J. John Sepkoski Jr. |year=1982 |month=March |title=Mass extinctions in the marine fossil record |journal=Science |volume=215 |issue=4539 |pages=pp. 1501–1503 |id={{doi|10.1126/science.215.4539.1501}} }}</ref> The last mass extinction occurred some 65 million years ago, when a meteorite collision probably triggered the extinction of the [[avian|non-avian]] [[dinosaur]]s and other large reptiles, but spared small animals such as [[mammal]]s, which then resembled [[shrew]]s. Over the past 65 million years, mammalian life diversified.<ref>{{cite book |last=Margulis |first=Lynn |coauthors=Dorian Sagan |year=1995 |title=What is Life? |publisher=Simon & Schuster |location=New York |id=ISBN 0-684-81326-2 |pages=p. 145}}</ref>

Since the [[Cambrian explosion]] there have been five distinctly identifiable [[Extinction event|mass extinctions]]. The last mass extinction occurred some 65 million years ago, when a meteorite collision probably triggered the extinction of the [[avian|non-avian]] [[dinosaur]]s and other large reptiles, but spared small animals such as [[mammal]]s, which then resembled [[shrew]]s. Over the past 65 million years, mammalian life diversified. ISBN 0-684-81326-2

Several million years ago, a species of small African ape gained the ability to stand upright.<ref>{{cite book |last=Margulis |first=Lynn |coauthors=Dorian Sagan |year=1995 |title=What is Life? |publisher=Simon & Schuster |location=New York |id=ISBN 0-684-81326-2}}</ref> 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 [[Oxygen Catastrophe]], produced by the proliferation of algae during the [[Siderian]] period, required about 300 million years to culminate.)

Several million years ago, a species of small African ape gained the ability to stand upright.<ref>{{cite book |last=Margulis |first=Lynn |coauthors=Dorian Sagan |year=1995 |title=What is Life? |publisher=Simon & Schuster |location=New York |id=ISBN 0-684-81326-2}}</ref> 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 [[Oxygen Catastrophe]], produced by the proliferation of algae during the [[Siderian]] period, required about 300 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 = 469-76; discussion 476-7 | year = 1989 | id = PMID 2574887}}</ref><ref>{{cite journal | author = Novacek M, Cleland E | title = The current biodiversity extinction event: scenarios for mitigation and recovery | journal = Proc Natl Acad Sci U S A | volume = 98 | issue = 10 | pages = 5466-70 | year = 2001 | id = PMID 11344295}}</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 years.<ref>"The mid-Holocene extinction of silver fir ''(Abies alba)'' in the ..." [http://www.springerlink.com/index/D85T53513002564V.pdf pdf]</ref>  The extent of the current extinction event is still being researched, debated and calculated by biologists.<ref>See, e.g. [http://park.org/Canada/Museum/extinction/holmass.html], [http://park.org/Canada/Museum/extinction/extincmenu.html], [http://park.org/Canada/Museum/extinction/patterns.html]</ref>

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 = Novacek M, Cleland E | title = The current biodiversity extinction event: scenarios for mitigation and recovery | journal = Proc Natl Acad Sci U S A | volume = 98 | issue = 10 | pages = 5466-70 | year = 2001 | id = PMID 11344295}}</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 years.<ref>"The mid-Holocene extinction of silver fir ''(Abies alba)'' in the ..." [http://www.springerlink.com/index/D85T53513002564V.pdf pdf]</ref>  The extent of the current extinction event is still being researched, debated and calculated by biologists.<ref>See, e.g. [http://park.org/Canada/Museum/extinction/holmass.html], [http://park.org/Canada/Museum/extinction/extincmenu.html], [http://park.org/Canada/Museum/extinction/patterns.html]</ref>

===Atmosphere, climate and weather===

===Atmosphere, climate and weather===