Nature is a concept with two major sets of inter-related meanings, referring on the one hand to the things which are natural, or subject to the normal working of "laws of nature", or on the other hand to the essential properties and causes of those things to be what they naturally are, or in other words the laws of nature themselves.

How to understand the meaning and significance of nature has been a consistent theme of discussion within the history of Western Civilization, in the philosophical fields of metaphysics and epistemology, as well as in theology and science. The study of natural things and the regular laws which seem to govern them, as opposed to discussion about what it means to be natural, is the area of natural science.

The word "nature" derives from Latin nātūra, a philosophical term derived from the verb for birth, which was used as a translation for the earlier Ancient Greek term phusis which was derived from the verb for natural growth, for example that of a plant. Already in classical times, philosophical use of these words combined two related meanings which have in common that they refer to the way in which things happen by themselves, "naturally", without "interference" from human deliberation, divine intervention, or anything outside of what is considered normal for the natural things being considered.

Understandings of nature depend on the subject and age of the work where they appear. For example Aristotle's explanation of natural properties differs from what is meant by natural properties in modern philosophical and scientific works, which can also differ from other scientific and conventional usage.

Classical nature and Aristotelian metaphysics[link]

The Physics (from physis, Greek for "nature") is Aristotle's principal work on nature. In Physics II.1, Aristotle defines a nature as "a source or cause of being moved and of being at rest in that to which it belongs primarily".^[1] In other words, a nature is the principle within a natural raw material that is the source of tendencies to change or rest in a particular way unless stopped. For example a rock would fall unless stopped. Natural things stand in contrast to artifacts, which are formed by human artifice, not because of an innate tendency. (The raw materials of a bed have no tendency to become a bed.) In terms of Aristotle's theory of four causes, the word natural is applied both to the innate potential of matter cause and the forms which the matter tends to become naturally.^[2]

According to Leo Strauss^[3], the beginning of Western philosophy involved the "discovery or invention of nature" and the "pre-philosophical equivalent of nature" was supplied by "such notions as 'custom' or 'ways'". In ancient Greek philosophy on the other hand, Nature or natures are ways that are "really universal" "in all times and places". What makes nature different is that it presupposes not only that not all customs and ways are equal, but also that one can "find one's bearings in the cosmos" "on the basis of inquiry" (not for example on the basis of traditions or religion). To put this "discovery or invention" into the traditional terminology, what is "by nature" is contrasted to what is "by convention". The concept of nature taken this far remains a strong tradition in modern western thinking. Science, according to Strauss' commentary of Western history is the contemplation of nature, while technology was or is an attempt to imitate it^[4].

Going further, the philosophical concept of nature or natures as a special type of causation - for example that the way particular humans are is partly caused by something called "human nature" is an essential step towards Aristotle's teaching concerning causation, which became standard in all Western philosophy until the arrival of modern science.

Aristotle

Whether it was intended or not, Aristotle's inquiries into this subject were long felt to have resolved the discussion about nature in favor of one solution. In this account, there are four different types of cause:

• The material cause is the "raw material" - the matter which undergoes change. One of the causes of a statue being what it is might be that it is bronze. All meanings of the word nature encompass this simple meaning.
• The efficient cause is the motion of another thing, which makes a thing change, for example a chisel hitting a rock causes a chip to break off. This is the way which the matter is forming into a form so that it become substance like what Aristotle said that a substance must have a form and matter in order to call it substance. This is the motion of changing a single being into two. This is the most obvious way in which cause and effect works, as in the descriptions of modern science. But according to Aristotle, this does not yet explain that of which the motion is, and we must "apply ourselves to the question whether there is any other cause per se besides matter"^[5].
• The formal cause is the form or idea which serves as a template towards which things develop - for example following an approach based upon Aristotle we could say that a child develops in a way partly determined by a thing called "human nature". Here, nature is a cause.
• The final cause is the aim towards which something is directed. For example a human aims at something perceived to be good, as Aristotle says in the opening lines of the Nicomachean Ethics.

The formal and final cause are an essential part of Aristotle's "Metaphysics" - his attempt to go beyond nature and explain nature itself. In practice they imply a human-like consciousness involved in the causation of all things, even things which are not man-made. Nature itself is attributed with having aims^[6].

The artificial, like the conventional therefore, is within this branch of Western thought, traditionally contrasted with the natural. Technology was contrasted with science, as mentioned above. And another essential aspect to this understanding of causation was the distinction between the accidental properties of a thing and the substance - another distinction which has lost favor in the modern era, after having long been widely accepted in medieval Europe.

To describe it another way, Aristotle treated organisms and other natural wholes as existing at a higher level than mere matter in motion. Aristotle's argument for formal and final causes is related to a doctrine about how it is possible that people know things: "If nothing exists apart from individual things, nothing will be intelligible; everything will be sensible, and there will be no knowledge of anything—unless it be maintained that sense-perception is knowledge"^[7]. Those philosophers who disagree with this reasoning therefore also see knowledge differently than Aristotle.

Aristotle then, described nature or natures as follows, in a way quite differently to modern science...

"Nature" means:
(a) in one sense, the genesis of growing things — as would be suggested by pronouncing the υ of φύσις^[8] long—and
(b) in another, that immanent thing from which a growing thing first begins to grow.
(c) The source from which the primary motion in every natural object is induced in that object as such. All things are said to grow which gain increase through something else by contact and organic unity (or adhesion, as in the case of embryos). Organic unity differs from contact; for in the latter case there need be nothing except contact, but in both the things which form an organic unity there is some one and the same thing which produces, instead of mere contact, a unity which is organic, continuous and quantitative (but not qualitative). Again, "nature" means
(d) the primary stuff, shapeless and unchangeable from its own potency, of which any natural object consists or from which it is produced; e.g., bronze is called the "nature" of a statue and of bronze articles, and wood that of wooden ones, and similarly in all other cases. For each article consists of these "natures," the primary material persisting. It is in this sense that men call the elements of natural objects the "nature," some calling it fire, others earth or air or water, others something else similar, others some of these, and others all of them. Again in another sense "nature" means
(e) the substance of natural objects; as in the case of those who say that the "nature" is the primary composition of a thing, or as Empedocles says: Of nothing that exists is there nature, but only mixture and separation of what has been mixed; nature is but a name given to these by men. Hence as regards those things which exist or are produced by nature, although that from which they naturally are produced or exist is already present, we say that they have not their nature yet unless they have their form and shape. That which comprises both of these exists by nature; e.g. animals and their parts. And nature is both the primary matter (and this in two senses: either primary in relation to the thing, or primary in general; e.g., in bronze articles the primary matter in relation to those articles is bronze, but in general it is perhaps water—that is if all things which can be melted are water) and the form or essence, i.e. the end of the process, of generation. Indeed from this sense of "nature," by an extension of meaning, every essence in general is called "nature," because the nature of anything is a kind of essence. From what has been said, then, the primary and proper sense of "nature" is the essence of those things which contain in themselves as such a source of motion; for the matter is called "nature" because it is capable of receiving the nature, and the processes of generation and growth are called "nature" because they are motions derived from it. And nature in this sense is the source of motion in natural objects, which is somehow inherent in them, either potentially or actually.

— Metaphysics 1014b-1015a, translated by Hugh Tredennick, emphasis added.^[9]

It might be argued, as indeed it has been, that this type of theory represented an over-simplifying diversion from the debates within Classical philosophy, possibly even that Aristotle saw it as a simplification or summary of the debates himself. But in any case the theory of the four causes became a standard part of any advanced education in the Middle Ages.

Modern science and laws of nature: trying to avoid metaphysics[link]

A Renaissance representation of Democritus the laughing philosopher, by Agostino Carracci

Francis Bacon

In contrast, Modern Science took its distinctive turn with Francis Bacon, who rejected the four distinct causes, and saw Aristotle as someone who "did proceed in such a spirit of difference and contradiction towards all antiquity: undertaking not only to frame new words of science at pleasure, but to confound and extinguish all ancient wisdom". He felt that lesser known Greek philosophers such as Democritus "who did not suppose a mind or reason in the frame of things", have been arrogantly dismissed because of Aristotelianism leading to a situation in his time wherein "the search of the physical causes hath been neglected, and passed in silence".^[10]

And so Bacon advised...

Physic doth make inquiry, and take consideration of the same natures : but how? Only as to the material and efficient causes of them, and not as to the forms. For example; if the cause of whiteness in snow or froth be inquired, and it be rendered thus, that the subtile intermixture of air and water is the cause, it is well rendered ; but, nevertheless, is this the form of whiteness? No; but it is the efficient, which is ever but vehiculum formæ. This part of metaphysique I do not find laboured and performed...

— Francis Bacon, Advancement of Learning II.VII.6

In his Novum Organum Bacon argued that the only forms or natures we should hypothesize are the "simple" (as opposed to compound) ones such as the ways in which heat, movement, etc. work. For example in aphorism 51 he writes:

51. The human understanding is, by its own nature, prone to abstraction, and supposes that which is fluctuating to be fixed. But it is better to dissect than abstract nature; such was the method employed by the school of Democritus, which made greater progress in penetrating nature than the rest. It is best to consider matter, its conformation, and the changes of that conformation, its own action, and the law of this action or motion, for forms are a mere fiction of the human mind, unless you will call the laws of action by that name.

Following Bacon's advice, the scientific search for the formal cause of things is now replaced by the search for “laws of nature” or “laws of physics” in all scientific thinking. To use Aristotle’s well-known terminology these are descriptions of efficient cause, and not formal cause or final cause. It means modern science limits its hypothesizing about non-physical things to the assumption that there are regularities to the ways of all things which do not change.

These general laws, in other words, replace thinking about specific "laws", for example "human nature". In modern science, human nature is part of the same general scheme of cause and effect, obeying the same general laws, as all other things. The above-mentioned difference between accidental and substantial properties, and indeed knowledge and opinion, also disappear within this new approach that aimed to avoid metaphysics.

As Bacon knew, the term "laws of nature" was one taken from medieval Aristotelianism. St Thomas of Aquinas for example, defined law so that nature really was legislated to consciously achieve aims, like human law: "an ordinance of reason for the common good, made by him who has care of the community and promulgated"^[11]. In contrast, roughly contemporary with Bacon, Hugo Grotius described the law of nature as "a rule that [can] be deduced from fixed principles by a sure process of reasoning"^[12]. And later still, Montesquieu was even further from the original legal metaphor, describing laws vaguely as "the necessary relations deriving from the nature of things"^[13].

Thomas Hobbes

One of the most important implementors of Bacon's proposal was Thomas Hobbes, whose remarks concerning nature are particularly well-known. His most famous work, Leviathan, opens with the word "Nature" and then parenthetically defines it as "the art whereby God hath made and governes the world". Despite this pious description, he follows a Baconian approach. Following his contemporary, Descartes, Hobbes describes life itself as mechanical, caused in the same way as clockwork:

For seeing life is but a motion of Limbs, the beginning whereof is in some principall part within; why may we not say, that all Automata (Engines that move themselves by springs and wheeles as doth a watch) have an artificiall life?

On this basis, already being established in natural science in his lifetime, Hobbes sought to discuss politics and human life in terms of "laws of nature". But in the new modern approach of Bacon and Hobbes, and before them Machiavelli (who however never clothed his criticism of the Aristotelian approach in medieval terms like "laws of nature")^[14], such laws of nature are quite different to human laws: they no longer imply any sense of better or worse, but simply how things really are, and, when in reference to laws of human nature, what sorts of human behavior can be most relied upon.

"Late modern" nature[link]

Jean-Jacques Rousseau: a civilized man, but a person who questioned whether civilization was according to human nature.

Benjamin West's "The Death of General Wolfe". The section shows the Native American. West's portrayal of the Native American has been cited as an example of the "noble savage", a concept associated with Rousseau's Second Discourse. The Discourse itself used stories of great apes to help explain what man would be like in the state of nature.

Having disconnected the term "law of nature" from the original medieval metaphor of human-made law, the term "law of nature" is now used less than in early modern times.

To take the critical example of human nature, as discussed in ethics and politics, once early modern philosophers such as Hobbes had described human nature as whatever you could expect from a mechanism called a human, the point of speaking of human nature became problematic in some contexts.

In the late 18th century, Rousseau took a critical step in his Second Discourse, reasoning that human nature as we know it, rational, and with language, and so on, is a result of historical accidents, and the specific up-bringing of an individual. The consequences of this line of reasoning were to be enormous. It was all about the question of nature. In effect it was being claimed that human nature, one of the most important types of nature in Aristotelian thinking, did not exist as it had been understood to exist.

The survival of metaphysics[link]

The approach of modern science, like the approach of Aristotelianism, is apparently not universally accepted by all people who accept the concept of nature as a reality which we can pursue with reason.

Bacon and other opponents of Metaphysics claim that all attempts to go beyond nature are bound to fall into the same errors, but Metaphysicians themselves see differences between different approaches.

Immanuel Kant for example, expressed the need for a Metaphysics in quite similar terms to Aristotle.

...though we cannot know these objects as things in themselves, we must yet be in a position at least to think them as things in themselves; otherwise we should be landed in the absurd conclusion that there can be appearance without anything that appears.

— Critique of Pure Reason pp. Bxxvi-xxvii

As in Aristotelianism then, Kantianism claims that the human mind must itself have characteristics which are beyond nature, metaphysical, in some way. Specifically Kant argued that the human mind comes ready-made with a priori programming, so to speak, which allows it to make sense of nature.

The study of nature without metaphysics[link]

Authors from Nietzsche to Richard Rorty have claimed that science, the study of nature, can and should exist without metaphysics. But this claim has always been controversial. Authors like Bacon and Hume never denied that their use of the word "nature" implied a metaphysics, but tried to follow Machiavelli's approach of talking about what works, instead of claiming to understand what seems impossible to understand.

Eastern civilization and the philosophical question of nature[link]

This section has been nominated to be checked for its neutrality. Discussion of this nomination can be found on the talk page. (November 2010)

The discussion so far above focuses upon the Western philosophical tradition, where the word "nature" has a very specific history. But despite claims mentioned above to the contrary, it is not universally accepted that Greek philosophy was the one occasion upon which the concept of nature was discovered and emphasized in this way.

In Chinese, the term "nature" may be rendered as either ziran (自然), or xing (性). The same terms appear in the philosophical literature of nations that adopted the Chinese writing such as Japan and Korea. In the early Chinese literature, nature appears in what might be called, a "pre-Socratic" sense akin to Dao (道), or "the Way", in antiquity, similar to 法 fa or "Law").^{[citation needed]} Indeed, in ancient Daoism, the Way is above all, the way of nature (自然之道 ziran zhi dao). The term "Dao" is sometimes compared to the enigmatic way Heraclitus used "Logos". In older extant Chinese texts (e.g. 黃帝四經 Huangdi Sijing, or Scripture of the Yellow Emperor), Dao (as the Dao of nature) has at once a metaphysical and legal character, strongly suggesting that the source of legislation is to be found in the nature of things.^{[citation needed]} While at first, the nature of things was intended as an impulse (志 zhi or 心 xin), in later Confucianism the distinction would be stressed between mind and will, or between life and the "principle" or "mind" of life (性 xing). In Mencius, for instance, life and its principle are juxtaposed in a way that later scholars establish to be mind, as a principle, independent of human will (thus, for example, the mind of nature). Confucius articulates, a question of natural principle, or the standard of interpretation of names. When Confucius seeks beyond the plane of convention or custom—when he reaches out to the roots of names—he does not find the will of gods and spirits. What he did find remains the subject of interpretation for the scholarship of thousands of years. That subject is usually called nature or the mind thereof.^{[citation needed]}

The philosophical tradition of Legalism, generally may be understood as a quest for the mind of nature,^{[citation needed]} and as a struggle to preserve that quest against "heretical" (邪道 xiadao) tendencies to seek nature (or the mind thereof) outside the law. Accordingly, throughout ancient China, scholarship of the period generally remained tied to political problems, or problems of legal interpretation. Metaphysical problems were understood as eminently legal problems (and vice versa),^{[citation needed][contradictory]} so that the interpretation or study (學 xue) of Justice or Right (義 yi) emergeed as the philosophical activity par excellence: to ask "what is Justice?", a favorite question of Confucius, is both to probe the essential (interior) nature of names, or "to know speech" (知言 zhiyan), in principle, by virtue of the constituent names.

The rise of Buddhism in ancient China, stimulated the debate on nature once again. Now^[when?] nature was unequivocally^{[citation needed]} regarded as the mind of all things, or as "Buddha-nature" (佛性 foxing). This was also the mind of "the Empire" (天下 tianxia), or the monarchic principle common to all nations,^{[citation needed]} (hence an identification—notably in Japan—of Buddha as the essence of the Emperor). nature, regarded as utterly beyond both imagination and speech, was that which "cannot be imagined or deliberated", (不可思議 bukesiyi) In the act of being revealed universally, that which is neither externally, nor internally, accessible to the delusional sensory capabilities of one's misappropriating ego disappears.^[vague] Facing of the threat of a solar eclipse, or the depths of the problem of nature,^[vague] and the consequent decay of civil life into "chaos"^[vague] or (亂 luan), the Chan or Zen (禪) revival of "the Buddha Way" (佛道 fodao) emerged. This emphasized the original coincidence^[vague] of the Buddha mind (the metaphysical) and the everyday mind (the political). The name Buddha, refers neither to something outside the ego (我 wo), nor to ego as a self-appropriating poetic faculty.^[vague] From this approach, the Buddha was understood as "original" nature, or original mind, yet "very ordinary" because Buddha is not the constitutive principle of an order beyond the civil order, or public morality. Of "this very order",^[which?] not the ego's deluded physical motion or nominal forms, the ordering principle of both speech and sensory experience "gathers" common experience under a global scope with universal names declared as "direct pointers", for example, (直指 zhi) to "the moon" (月 yue) or "the original mind". The foremost task of a student of the way was thus to recover the constitutive principle of the common experience, their original mind.^{[citation needed]} When understood in this way, "original mind" was thought to conform with normative public morality. Ultimately,^[why?] Chan was no less a return to "piety"^{[citation needed]} (孝 xiao), than it was a return to nature as the common principle of the constitution of civil life.

See also[link]

• Nature
• Natural philosophy
• Human nature
• Causality
• Reality
• Truth
• A priori and a posteriori (philosophy)
• Platonism
• Idealism
• Aristotelianism
• Empiricism

References[link]

"Natural" and "Natural World" redirect here. For other uses, see Nature (disambiguation) and Natural (disambiguation).

Hopetoun Falls, Australia

Bachalpsee in the Swiss Alps

Lightning strikes during the eruption of the huge Galunggung volcano, West Java, in 1982.

Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general. It ranges in scale from the subatomic to the cosmic.

The word nature is derived from the Latin word natura, or "essential qualities, innate disposition", and in ancient times, literally meant "birth".^[1] 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.^[2][3] 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.^[4][5]

Within the various uses of the word today, "nature" often refers to geology and wildlife. 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. 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 which 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 unnatural, the supernatural, or synthetic.

Earth[link]

View of the Earth, taken in 1972 by the Apollo 17 astronaut crew. This image is the only photograph of its kind to date, showing a fully sunlit hemisphere of the Earth.

Earth (or, "the earth") is the only planet presently 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 equatorial tropical to subtropical region.^[6] 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 outer surface is divided into several gradually migrating tectonic plates. The interior remains active, with a thick layer of plastic mantle and an iron-filled core that generates a magnetic field.

The atmospheric conditions have been significantly altered from the original conditions by the presence of life-forms,^[7] 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,^[8] 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.^[9][10]

Geology[link]

Three types of geological plate tectonic boundaries.

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, structure, physical properties, dynamics, and 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 mineral and hydrocarbon extraction, knowledge about and mitigation of natural hazards, some Geotechnical engineering fields, and understanding past climates and environments.

Geological evolution[link]

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 onto the surface or intrude into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows, blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and 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 deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates.

Historical perspective[link]

Plankton inhabit oceans, seas and lakes, and have existed in various forms for at least 2 billion years.^[11]

An animation of the Earth's hypothesized Pangaea separation.

Earth is estimated to have formed 4.54 billion years ago from the solar nebula, along with the Sun and other planets.^[12] The moon formed roughly 20 million years later. Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, most or all of which came from ice delivered by comets, produced the oceans and other water sources.^[13] The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago.^[14]

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 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.^[15]

There is significant evidence that a severe 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.^[16]

Since the Cambrian explosion there have been five distinctly identifiable mass extinctions.^[17] The last mass extinction occurred some 65 million years ago, when a meteorite collision probably triggered the extinction of the non-avian dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life diversified.^[18]

Several million years ago, a species of small African ape gained the ability to stand upright.^[19] 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 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.^[20][21] 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.^[22] The extent of the current extinction event is still being researched, debated and calculated by biologists.^[23]

Atmosphere, climate, and weather[link]

Lightning

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space

A tornado in central Oklahoma

The atmosphere of the Earth serves as a key factor in sustaining the planetary ecosystem. The thin layer of gases that envelops the Earth is held in place by the planet's gravity. Dry air consists of 78% nitrogen, 21% oxygen, 1% argon and other inert gases, carbon dioxide, etc.; but air also contains a variable amount of water vapor. The atmospheric pressure declines steadily with altitude, and has a scale height of about 8 kilometres at the Earth's surface: the height at which the atmospheric pressure has declined by a factor of e (a mathematical constant equal to 2.71...).^[24][25] The ozone layer of the Earth's atmosphere 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 lower part of the atmosphere, and serves as a convective system for redistributing heat. Ocean currents 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 regions much colder.

Weather can have both beneficial and harmful effects. Extremes in weather, such as tornadoes or hurricanes and cyclones, 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.

The planetary climate is a measure of the long-term trends in the weather. Various factors are known to influence the climate, including ocean currents, surface albedo, greenhouse gases, variations in the solar luminosity, and changes to the planet's orbit. Based on historical records, the Earth is known to have undergone drastic climate changes in the past, including ice ages.

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 being tilted relative to its orbital plane. Thus, at any given time during the summer or winter, one part of the planet 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 and southern hemispheres experience opposite seasons.

Weather is a chaotic system that is readily modified by small changes to the environment, so accurate weather forecasting is currently limited to only a few days.^{[citation needed]} Overall, two things are currently happening worldwide: (1) temperature is increasing on the average; and (2) regional climates have been undergoing noticeable changes.^[26]

Water on Earth[link]

The Iguazu Falls on the border between Brazil and Argentina

Water is a chemical substance that is composed of hydrogen and oxygen and is vital for all known forms of life.^[27] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface.^[28] On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation.^[29] Oceans hold 97% of surface water, glaciers and polar ice caps 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[link]

A view of the Atlantic Ocean from Leblon, Rio de Janeiro.

Earth's oceans (World Ocean)
Arctic Ocean Atlantic Ocean Indian Ocean Pacific Ocean Southern Ocean

An ocean is a major body of 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 continuous body of water that is customarily divided into several principal oceans and smaller seas. More than half of this area is over 3,000 meters (9,800 ft) 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.^[30][31] 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.^[32]

The major oceanic divisions are defined in part by the continents, various archipelagos, 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, bays and other names. There are also salt lakes, 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[link]

Lake Mapourika, New Zealand

A lake (from Latin 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 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.^[33][34] The only world other than Earth known to harbor lakes is 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 zones, and areas with ongoing or recent glaciation. Other lakes are found in endorheic basins 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 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[link]

The Westborough Reservoir (Mill Pond) in Westborough, Massachusetts.

A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens designed for aesthetic ornamentation, fish ponds designed for commercial fish breeding, and solar ponds designed to store thermal energy. Ponds and lakes are distinguished from streams via current speed. While currents in streams are easily observed, ponds and lakes possess thermally driven microcurrents and moderate wind driven currents. These features distinguish a pond from many other aquatic terrain features, such as stream pools and tide pools.

Rivers[link]

The Nile river in Cairo, Egypt's capital city

A river is a natural watercourse,^[35] usually freshwater, flowing toward 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,^[36] but this is not always the case, due to vagueness in the language.^[37] A river is part of the hydrological cycle. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (i.e., from glaciers).

Streams[link]

A stream is a flowing body of water with a current, confined within a bed and stream banks. In the United States a stream is classified as a watercourse less than 60 feet (18 metres) 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 corridor role in connecting 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, fluvial geomorphology, aquatic ecology, fish biology, riparian ecology and others.

Ecosystems[link]

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.^[38]

An aerial view of a human ecosystem. Pictured is the city of Chicago

Ecosystems are composed of a variety of abiotic and biotic components that function in an interrelated way.^[39] 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.

Central to the ecosystem concept is the idea that living organisms interact with every other element in their local 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."^[40] 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.^[41] The human ecosystem concept is grounded in the deconstruction of the human/nature dichotomy and the premise that all species are ecologically integrated with each other, as well as with the abiotic constituents of their biotope.^{[citation needed]}

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.^[42]

Wilderness[link]

Old growth European Beech forest in Biogradska Gora National Park, Montenegro.

Wilderness is generally defined as areas that have not been significantly modified by human activity. The WILD Foundation goes into more detail, defining wilderness as: "The most intact, undisturbed wild natural areas left on our planet – those last truly wild places that humans do not control and have not developed with roads, pipelines or other industrial infrastructure." Wilderness areas can be found in preserves, estates, farms, conservation preserves, ranches, national forests, national parks 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, conservation, solitude, and recreation. Some nature writers believe wilderness areas are vital for the human spirit and creativity,^[43] and some Ecologists consider wilderness areas to be an integral part of the planet's self-sustaining natural ecosystem (the biosphere). They may also preserve historic genetic traits and that they provide habitat for wild flora and fauna that may be difficult to recreate in zoos, arboretums or laboratories.

Life[link]

Female mallard and ducklings – reproduction is essential for continuing life

Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by organization, metabolism, growth, adaptation, response to stimuli and reproduction.^[44] Life may also be said to be simply the characteristic state of organisms.

Properties common to terrestrial organisms (plants, animals, fungi, protists, 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 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 biotic processes in turn alter or transform. From the broadest 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). Currently the entire Earth contains over 75 billion tons (150 trillion pounds or about 6.8 x 10¹³ kilograms) of biomass (life), which lives within various environments within the biosphere.^[45]

Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence.^[46] More than 2 million species of plant and animal life have been identified to date,^[47] and estimates of the actual number of existing species range from several million to well over 50 million.^[48][49][50] 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.^[51][52] The total number of species is presently in rapid decline.^[53][54][55]

Evolution[link]

An area of the Amazon Rainforest in Brazil. The tropical rainforests of South America contain the largest diversity of species on Earth.^[56][57]

Life is only known to exist on the planet Earth.(cf Astrobiology) The origin of life is still a poorly understood process, but it is thought to have occurred about 3.9 to 3.5 billion years ago during the hadean or archean eons on a primordial earth that had a substantially different environment than is found at present.^[58] 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.^[58]

The advent of photosynthesis in very basic forms of plant life worldwide allowed the sun's energy to be harvested to create conditions allowing for more complex life.^{[citation needed]} 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 development of yet more complex cells called eukaryotes.^[59] 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[link]

A microscopic mite Lorryia formosa.

The first form of life to develop on the Earth were microbes, and they remained the only form of life on the planet until about a billion years ago when multi-cellular organisms began to appear.^[60] Microorganisms are single-celled organisms that are generally microscopic, and smaller than the human eye can see. They include Bacteria, Fungi, Archaea and Protista.

These life forms are found in almost every location on the Earth where there is liquid water, including the interior of rocks within the planet.^[61] Their reproduction is both rapid and profuse. The combination of a high mutation rate and a horizontal gene transfer^[62] ability makes them highly adaptable, and able to survive in new environments, including outer space.^[63] They form an essential part of the planetary ecosystem. However some microorganisms are pathogenic and can post health risk to other organisms.

Plants and animals[link]

A selection of diverse plant species

There are many animal species on the planet

Originally Aristotle divided all living things between plants, which generally do not move fast enough for humans to notice, and animals. In Linnaeus' system, these became the kingdoms Vegetabilia (later Plantae) and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts. Bacterial life is sometimes included in flora,^[64][65] and some classifications use the term bacterial flora separately from plant flora.

Among the many ways of classifying plants are by regional floras, which, depending on the purpose of study, can also include fossil flora, remnants
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 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 eukaryotic and usually multicellular (although see Myxozoa), which separates them from bacteria, archaea and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls.

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues.^{[citation needed]} These include muscles, which are able to contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber. The eukaryotic cells possessed by all animals are surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and 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[link]

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.

Sochi dendrarium is an example of confluence of "natural" and a "made" environment

Although humans currently comprise only a minuscule proportion of the total living biomass on Earth, the 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 presently diminishing at an increasingly rapid pace.

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.^[66] Man-made threats to the Earth's natural environment include pollution, deforestation, and disasters such as oil spills. Humans have contributed to the extinction of many plants and animals.

Humans employ nature for both leisure and economic activities. The acquisition of natural resources for industrial use remains the primary component of the world's economic system.^{[citation needed]} Some activities, such as hunting and fishing, are used for both sustenance and leisure, often by different people. 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 properties of vegetation for healing,^[67] most modern human use of plants is through agriculture. The 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.^[68]

Aesthetics and beauty[link]

Pinguicula grandiflora, commonly known as a Butterwort

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, is 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.^[69] 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 (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. 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.^[70] This artistic movement also coincided with the 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 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".^[71]:281

Matter and energy[link]

The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density

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 percent of the total mass. The remainder is believed to consist of 23 percent cold dark matter and 73 percent dark energy.^[72] The exact nature of these components is still unknown and is currently under intensive investigation by physicists.

The behavior of matter and energy throughout the observable universe appears to follow well-defined physical laws. These laws have been employed to produce 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 constants^[73] that appear to be static across the observable universe.^[74] The values of these constants have been carefully measured, but the reason for their specific values remains a mystery.

Beyond Earth[link]

Planets and dwarf planets of the Solar System (Sizes to scale, distances not to scale)

NGC 4414 is a spiral galaxy in the constellation Coma Berenices about 56,000 light years 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 atmospheres of celestial bodies. Outer space is used to distinguish it from airspace (and terrestrial locations). There is no discrete boundary between the Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the Solar System is called interplanetary space, which passes over into interstellar space at what is known as the heliopause.

Outer space is certainly spacious, but it is far from empty.^{[citation needed]} Outer space is sparsely filled with several dozen types of organic molecules discovered to date by microwave spectroscopy, blackbody radiation left over from the big bang and the origin of the universe, and cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also some gas, plasma and dust, and small meteors. Additionally, there are signs of human life in outer space today, such as material left over from previous manned and unmanned launches which are a potential hazard to spacecraft. Some of this debris re-enters the atmosphere periodically.

Although the planet Earth is currently the only known body within the solar system to support life, current evidence suggests that in the distant past the planet Mars possessed bodies of liquid water on the surface.^[75] 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.^[76]

Conditions on the other terrestrial planets, Mercury and Venus, appear to be too harsh to support life as we know it.^{[citation needed]} But it has been conjectured that Europa, the fourth-largest moon of Jupiter, may possess a sub-surface ocean of liquid water and could potentially host life.^[77]

Recently, the team of Stéphane Udry have discovered a new planet named Gliese 581 g, which is an extrasolar planet orbiting the red dwarf star Gliese 581.^{[citation needed]} Gliese 581 g appears to lie in the habitable zone of space surrounding the star, and therefore could possibly host life as we know it.

See also[link]

	Environment portal
	Ecology portal
	Earth sciences portal
	Weather portal
	Astronomy portal

Media:

• Natural History, by Pliny the Elder
• Nature, by Ralph Waldo Emerson
• Nature, a prominent scientific journal
• National Wildlife (magazine), publication of the National Wildlife Federation
• Nature (TV series)

Organizations:

• The Nature Conservancy
• Nature Detectives

Science:

• Natural history
• Natural landscape

Philosophy:

• Mother Nature
• Nature (philosophy)
• Naturalism (philosophy): any of several philosophical stances, typically those descended from Materialism and Pragmatism that do not distinguish the supernatural from nature.^{[citation needed]} This includes the methodological naturalism of natural science, which makes the methodological assumption that observable events in nature are explained only by natural causes, without assuming either the existence or non-existence of the supernatural.
• Balance of nature (biological fallacy): A discredited concept of natural equilibrium in predator:prey dynamics.

Notes and references[link]