Nature Natural redirects here. For other uses of Nature, see Nature (disambiguation). For other uses of Natural, see Natural (disambiguation). Hopetoun Falls, Australia Bachalpseein the Swiss Alps Lightningstrikes during the eruption of the Galunggung volcano, West Java, in 1982. Nature, in the broadest sense, is equivalent to thenatural,physical, ormaterial worldoruniverse. Nature refers to the phenomenaof the physical world, and also to lifein general. It ranges in scale from the subatomicto the cosmic. The wordnatureis derived from the Latinwordnatura, or essential qualities, innate disposition, and in ancient times, literally meant birth. [ 1 ]Naturawas 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-Socraticphilosophers, and has steadily gained currency ever since. This usage continued during the advent of modern scientific methodin the last several centuries. [ 4 ] [ 5 ] Within the various uses of the word today, nature often refers togeology and wildlife ...and energyof 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 consciousnessor a human mind. Depending on the particular context, the term natural might also be distinguished from the unnatural, the supernatural, or synthetic. Earth Main articles: Earthand Earth science View of the Earth, taken in 1972 by the Apollo 17 astronautcrew. 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 planetpresently 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 planetand the fifth largest overall. Its most prominent climatic features are its two large polar regions, two relatively narrow temperatezones, and a wide equatorial tropicalto subtropicalregion. [ 6 ] Precipitationvaries widely with location, from several metres of water per year to less than a millimetre. 71 percent of the Earths 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 surfaceis divided into several gradually migrating tectonic plates. The interior remains active, with a thick layer of plastic mantleand an iron-filled core that generates a magnetic field. The atmosphericconditions 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 latitudeand 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 Main article: Geology Three types of geological plate tectonicboundaries. Geology is the scienceand 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 historyof 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 mineraland hydrocarbonextraction, knowledge about and mitigation of natural hazards, some Geotechnical engineeringfields, and understanding past climatesand environments. Geological evolution 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 depositiononto the surface or intrude into the overlying rock. Deposition can occur when sedimentssettle onto the surface of the Earth and later lithifyinto sedimentary rock, or when as volcanic materialsuch as volcanic ashor lavaflows, blanket the surface. Igneous intrusionssuch 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 deformedand/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 Main articles: History of the Earthand Evolution Planktoninhabit oceans, seas and lakes, and have existed in various forms for at least 2 billion years. [ 11 ] An animation showing the movement of the continents from the separation of Pangaeauntil the present day. Earth is estimated to have formed 4.54 billion years ago from the solar nebula, along with the Sunand 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 volcanicactivity produced the primordial atmosphere. Condensing water vapor, most or all of which came from icedelivered by comets, produced the oceansand 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 Pannotiawhich 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 glacialaction during the Neoproterozoicera 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 explosionin 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 66 million years ago, when a meteorite collision probably triggered the extinction of the non-avian dinosaursand other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 66 million years, mammalian life diversified. [ 18 ] Several million years ago, a species of small African apegained the ability to stand upright. [ 11 ]The subsequent advent of human life, and the development of agriculture and further civilizationallowed 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 algaeduring the Siderianperiod, required about 300 million years to culminate. The present era is classified as part of a mass extinction event, the Holocene extinctionevent, the fastest ever to have occurred. [ 19 ] [ 20 ]Some, such as E. O. Wilsonof Harvard University, predict that human destruction of the biospherecould cause the extinction of one-half of all species in the next 100 years. [ 21 ]The extent of the current extinction event is still being researched, debated and calculated by biologists. [ 22 ] Atmosphere, climate, and weather Lightning Blue light is scattered morethan other wavelengths by the gases in the atmosphere, giving the Earth a blue halowhen seen from space A tornado in central Oklahoma Main articles: Atmosphere of Earth, Climateand Weather The atmosphere of the Earth serves as a key factor in sustaining the planetary ecosystem. The thin layer of gasesthat envelops the Earth is held in place by the planets gravity. Dry airconsists of 78% nitrogen, 21% oxygen, 1% argonand 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 heightof about 8 kilometres at the Earths surface: the height at which the atmospheric pressure has declined by a factor of e(a mathematical constant equal to 2.71...). [ 23 ] [ 24 ]The ozone layerof the Earths atmosphere plays an important role in depleting the amount of ultraviolet(UV) radiation that reaches the surface. As DNAis 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 currentsare another important factor in determining climate, particularly the major underwater thermohaline circulationwhich distributes heat energy from the equatorial oceans to the polar regions. These currents help to moderate the differences in temperaturebetween 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 regionsmuch colder. Weather can have both beneficial and harmful effects. Extremes in weather, such as tornadoesor hurricanesand 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 planets 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 climateat the equator to the polar climatein the northern and southern extremes. Weather is also influenced by the seasons, which result from the Earths axisbeing tiltedrelative 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 northernand southernhemispheres experience opposite seasons. Weather is a chaotic systemthat is readily modified by small changes to the environment, so accurate weather forecastingis 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. [ 25 ] Water on Earth The Iguazu Fallson the border between Braziland Argentina Main article: Water Wateris a chemical substancethat is composed of hydrogenand oxygenand is vital for all known forms of life. [ 26 ]In typical usage,waterrefers only to its liquidform or state, but the substance also has a solidstate, ice, and a gaseousstate, water vaporor steam. Water covers 71% of the Earths surface. [ 27 ]On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifersand 0.001% in the airas vapor, clouds(formed of solid and liquid water particles suspended in air), and precipitation. [ 28 ] [ 29 ] Oceanshold 97% of surface water, glaciersand polar ice caps2.4%, and other land surface water such as rivers, lakesand ponds0.6%. Additionally, a minute amount of the Earths water is contained within biological bodies and manufactured products. Oceans A view of the Atlantic Oceanfrom Leblon, Rio de Janeiro. Main article: Ocean An oceanis a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earths surface(an area of some 361 million square kilometers) is covered by ocean, a continuous body of waterthat is customarily divided into several principal oceans and smaller seas. More than half of this area is over 3,000 meters (9,800 feet) deep. Average oceanic salinityis 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 Oceanor 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 Oceanand the Arctic Ocean. Smaller regions of the oceans are called seas, gulfs, baysand 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 Seaand the Great Salt Lake. Lakes Lake Mapourika, New Zealand Main article: Lake A lake(from Latinlacus) is a terrain feature(or physical feature), a body of liquidon 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, Saturns largest moon, which has lakes of ethane, most likely mixed with methane. It is not known if Titans lakes are fed by rivers, though Titans 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 basinsor 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 The Westborough Reservoir (Mill Pond) in Westborough, Massachusetts. Main article: Pond Apondis a bodyof 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 gardensdesigned for aesthetic ornamentation, fish pondsdesigned for commercial fish breeding, and solar pondsdesigned to store thermal energy. Ponds and lakes are distinguished from streams via currentspeed. 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 poolsand tide pools. Rivers The Nileriver in Cairo, Egypts capital city Main article: River A riveris a natural watercourse, [ 35 ]usually freshwater, flowing toward an ocean, a lake, a seaor 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 isBurnin Scotland and North-east England. Sometimes a river is said to be larger than a creek, [ 36 ][ dead link]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 precipitationthrough surface runoff, groundwaterrecharge, springs, and the release of stored water in natural ice and snowpacks (i.e., from glaciers). Streams A rocky streamin Hawaii Main article: Stream A stream is a flowing body of water with a current, confined within a bedand stream banks. In the United Statesa 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 fishand wildlifemigration. The biological habitatin the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridorrole in connecting fragmented habitatsand 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 ecologyand others. Ecosystems Loch Lomondin Scotland forms a relatively isolated ecosystem. The fish community of this lake has remained unchanged over a very long period of time. [ 38 ] Lush green Aravalli Mountain Range in the Desert country- Rajasthan, India. A wonder how such greenery can exist in hot Rajasthan, a place well known for its Thar Desert An aerial view of a human ecosystem. Pictured is the city of Chicago Main articles: Ecologyand Ecosystem Ecosystems are composed of a variety of abioticand bioticcomponents 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 organismsinteract 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 energyand matterbetween themselves as
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