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مشاهدة النسخة كاملة : the Earth

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06-27-2014, 10:10 PM
the Earth

Earth (or the Earth) is that the third planet from the Sun and therefore the densest and fifth-largest of the eight planets in the scheme. it's also the most important of the star System's four terrestrial planets. it's generally mentioned because the World, the Blue Planet,[20] or by its Latin name, Terra.[note 6]
Home to a lot of species including humans, Earth is presently the sole astronomical body where life is understood to exist.[21] the earth formed four.54 billion years ago, and life appeared on its surface at intervals one billion years.[22] Earth's biosphere has considerably altered the atmosphere and other abiotic conditions on the earth, enabling the proliferation of aerobic organisms moreover because the formation of the ozone layer that, beside Earth's magnetic field, blocks harmful radiation, permitting life ashore.[23] The physical properties of the planet, moreover as its geological history and orbit, have allowed life to persist throughout this period. the earth is expected to continue supporting life for at least another five hundred million years.[24][25]
Earth's outer surface is divided into many rigid segments, or tectonic plates, that migrate across the surface over periods of the many a lot of years. regarding seventy one of the surface is covered with salt water oceans, the rest consisting of continents and islands that together have many lakes and other sources of water contributive to the hydrosphere. Liquid water, necessary for all famed life, isn't famed to exist in equilibrium on any other planet's surface.[note 7] Earth's poles are principally covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a cast-iron inner core.
Earth interacts with other objects in space, especially the Sun and therefore the Moon. At present, Earth orbits the Sun once each 366.26 times it rotates regarding its own axis, that is equal to 365.26 star days, or one year.[note 8] The Earth's axis of rotation is canted 23.4° removed from the perpendicular of its plane, manufacturing seasonal differences on the planet's surface with a amount of 1 year (365.24 star days).[26] Earth's only famed natural satellite, the Moon, that began orbiting it regarding four.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. Between roughly three.8 billion and four.1 billion years ago, various asteroid impacts throughout the Late heavy Bombardment caused important changes to the greater surface atmosphere.
Both the natural resources of the earth, moreover because the product of the biosphere, contribute resources that are accustomed support a global human population. These inhabitants are sorted into regarding two hundred freelance sovereign states, that act through diplomacy, travel, trade, and group action. Human cultures have developed many views of the earth, including personification as a divinity, a belief in a flat Earth or in the Earth because the center of the universe, Associate in Nursingd a modern perspective of the world as an integrated atmosphere that requires situation.

Scientists have been able to reconstruct detailed information regarding the planet's past. The earliest dated scheme material was formed four.5672 ± 0.0006 billion years ago,[27] and by four.54 billion years ago (within Associate in Nursing uncertainty of 1%)[22] the planet and therefore the other planets in the scheme had formed out of the star nebula—a disk-shaped mass of mud and gas left over from the formation of the Sun. This assembly of the planet through accretion was therefore largely completed at intervals 10–20 million years.[28] at the start melted , the outer layer of the earth Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed shortly thereafter, 4.53 billion years ago.[29]
The current accord model[30] for the formation of the Moon is that the large impact hypothesis, within which the Moon was created when a Mars-sized object (sometimes referred to as Theia) with regarding 100 percent of the planet's mass[31] wedged the Earth in a glancing blow.[32] in this model, a number of this object's mass would have united with the planet and some would have been ejected into space, however enough material would have been sent into orbit to coalesce into the Moon.
Outgassing and volcanic activity produced the early atmosphere of the planet. condensing water vapour, augmented by ice and liquid water delivered by asteroids and therefore the larger proto-planets, comets, and trans-Neptunian objects produced the oceans.[33] The newly formed Sun was only 70th of its present luminousness, however proof shows that the first oceans remained liquid—a contradiction dubbed the faint young Sun contradiction in terms. a mixture of greenhouse gases and better levels of star activity served to raise the layer temperature, preventing the oceans from phase transition over.[34] By 3.5 billion years ago, the Earth's magnetic field was established, that helped stop the atmosphere from being stripped away by the solar radiation.[35]
Two major models have been proposed for the rate of continental growth:[36] steady growth to the present-day[37] and ascension early in Earth history.[38] Current analysis shows that the second possibility is most likely, with fast initial growth of continental crust[39] followed by a long steady continental area.[40][41][42] On time scales lasting many a lot of years, the surface regularly reshaped as continents formed and skint up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (Ma), one in all the earliest famed supercontinents, Rodinia, began to interrupt apart. The continents later recombined to form Pannotia, 600–540 Ma, then finally Pangea, that skint apart 180 Ma.[43]

At present, Earth provides the sole example of Associate in Nursing atmosphere that has given rise to the evolution of life.[44] highly energetic chemistry is believed to own produced a self-replicating molecule around four billion years ago and 0.5 a billion years later the last common antecedent of all life existed.[45] the development of chemical change allowed the Sun's energy to be harvested directly by life forms; the resultant element accumulated in the atmosphere and formed a layer of gas (a sort of molecular element [O3]) in the higher atmosphere. The incorporation of smaller cells at intervals larger ones resulted in the development of complicated cells referred to as eukaryotes.[46] True multicellular organisms formed as cells at intervals colonies became more and more specialised. assisted by the absorption of harmful ultraviolet by the ozone layer, life settled the surface of Earth.[47]
Since the Sixties, it's been hypothesized that severe glacial action between 750 and 580 Ma, throughout the Neoproterozoic, covered abundant of the earth in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of explicit interest as a result of it preceded the Cambrian explosion, when multicellular life forms began to proliferate.[48]
Following the Cambrian explosion, regarding 535 Ma, there have been five major mass extinctions.[49] the foremost recent such event was 65 Ma, when Associate in Nursing asteroid impact triggered the extinction of the (non-avian) dinosaurs and other large reptiles, however spared some little animals such as mammals, that then resembled shrews. Over the past 65 million years, class life has wide-ranging, and several other million years ago Associate in Nursing African ape-like animal such as Orrorin tugenensis gained the power to face upright.[50] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, that allowed the evolution of the mankind. the development of agriculture, then civilization, allowed humans to influence the planet in a short time span as no other life form had,[51] moving each the character and quantity of other life forms.
The present pattern of ice ages began regarding 40 Ma then intensified throughout the pleistocene regarding three Ma. High-latitude regions have since undergone continual cycles of glaciation and thaw, continuance each 40–100,000 years. The last continental glaciation concluded ten,000 years ago.[52]

The future of the earth is closely tied to that of the Sun. As a result of the steady accumulation of chemical element at the Sun's core, the star's total luminousness can slowly increase. The luminousness of the Sun can grow by 100 percent over consequent one.1 Gyr (1.1 billion years) and by 400th over consequent three.5 Gyr.[53] Climate models indicate that the increase in radiation reaching the planet is likely to own dire consequences, including the loss of the planet's oceans.[54]
The Earth's increasing surface temperature can accelerate the inorganic carbon dioxide cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in roughly five hundred million[24] to 900 million years. the shortage of vegetation can result in the loss of element in the atmosphere, so animal life can become extinct at intervals many million additional years.[55] once another billion years all surface water can have disappeared[25] and therefore the mean world temperature can reach seventy °C[55] (158 °F). the planet is expected to be effectively habitable for regarding another five hundred million years from that time,[24] though this may be extended up to two.3 billion years if the nitrogen is far from the atmosphere.[56] even if the Sun were eternal and stable, the continued internal cooling of the planet would result in a loss of abundant of its carbon dioxide due to reduced volcanism,[57] and 35th of the water in the oceans would descend to the mantle due to reduced steam discharge from mid-ocean ridges.[58]
The Sun, as a part of its evolution, can become a red giant star in regarding five Gyr. Models predict that the Sun can expand intent on regarding 250 times its present radius, roughly one AU (150,000,000 km).[53][59] Earth's fate is a smaller amount clear. As a red giant star, the Sun can lose roughly 30 minutes of its mass, so, without recurrent event effects, the planet can move to Associate in Nursing orbit one.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. the earth was so at the start expected to escape enclosure by the swollen Sun's distributed outer atmosphere, tho' most, if not all, remaining life would have been destroyed by the Sun's accumulated luminousness (peaking at regarding 5000 times its present level).[53] but, a 2008 simulation indicates that Earth's orbit can decay due to recurrent event effects and drag, causing it to enter the red giant star Sun's atmosphere and be volatilized.[59]

The automatically rigid outer layer of the planet, the geosphere, is broken into pieces referred to as tectonic plates. These plates are rigid segments that move in reference to one another at one in all 3 forms of plate boundaries: focussed boundaries, at that two plates close, Divergent boundaries, at that two plates are force apart, and rework boundaries, within which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation will occur on these plate boundaries.[85] The tectonic plates ride on top of the layer, the solid however less-viscous a part of the layer that can flow and move along with the plates,[86] and their motion is powerfully in addition to convection patterns within the Earth's mantle.
As the tectonic plates migrate across the earth, the ocean floor is subducted underneath the leading edges of the plates at focussed boundaries. At an equivalent time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. the combination of those processes regularly recycles the oceanic crust into the mantle. thanks to this utilisation, most of the ocean floor is a smaller amount than 100 million years in age. The oldest oceanic crust is found in the Western Pacific, Associate in Nursingd has an calculable age of regarding two hundred million years.[87][88] By comparison, the previousest dated continental crust is 4030 million years old.[89]
Other notable plates embody the Indian Plate, the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and therefore the Scotia Plate in the southern atlantic ocean. The Australian Plate united with the Indian Plate between fifty and fifty five million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of seventy five mm/yr[90] and therefore the Pacific Plate moving 52–69 mm/yr. At the opposite extreme, the slowest-moving plate is that the Eurasian Plate, progressing at a typical rate of regarding twenty one mm/yr.[91]

The Earth's atmosphere has no definite boundary, slowly becoming diluent and attenuation into outer space. Three-quarters of the atmosphere's mass is contained at intervals the first eleven metric linear unit of the planet's surface. This lowest layer is termed the troposphere. Energy from the Sun heats this layer, and therefore the surface below, causing growth of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospherical circulation that drives the weather and climate through distribution of heat energy.[110]
The primary atmospherical circulation bands carries with it the trade winds in the equatorial region below 30° latitude and therefore the westerlies in the mid-latitudes between 30° and 60°.[111] Ocean currents are vital factors in deciding climate, particularly the thermohaline circulation that distributes heat energy from the equatorial oceans to the polar regions.[112]
Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. when atmospherical conditions permit Associate in Nursing uplift of heat, humid air, this water condenses and settles to the surface as precipitation.[110] Most of the water is then transported to lower elevations by river systems and usually came back to the oceans or deposited into lakes. This water cycle may be a very important mechanism for supporting life ashore, and may be a primary factor in the erosion of surface options over geological periods. Precipitation patterns vary widely, ranging from many meters of water per year to but a mm. atmospherical circulation, topological options and temperature variations verify the common precipitation that falls in each region.[113]
The amount of solar power reaching the Earth's decreases with increasing latitude. At higher latitudes the daylight reaches the surface at a lower angles and it should taste thicker columns of the atmosphere. As a result, the mean annual air temperature puzzled level decreases by regarding 0.4°C per per degree of latitude removed from the equator.[114] the planet are often sub-divided into specific angular distance belts of roughly homogeneous climate. ranging from the equator to the polar regions, these are the tropical (or equatorial), semitropical, temperate and polar climates.[115] Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air plenty. The unremarkably used Köppen climate classification system (as modified by Wladimir Köppen's student Rudolph Geiger) has five broad teams (humid tropics, arid, humid middle latitudes, continental and cold polar), that are more divided into additional specific subtypes.[111]

Cartography, the study and practice of map creating, and vicariously geography, have historically been the disciplines dedicated to depiction the planet. Surveying, the determination of ********s and distances, and to a lesser extent navigation, the determination of position and direction, have developed aboard cartography and geography, providing and suitably quantifying the requisite information.
Earth has roughly half-dozen,910,000,000 human inhabitants as of Apr twenty five, 2011.[155] Projections indicate that the world's human population can reach seven billion in early 2012 and 9.2 billion in two050.[156] Most of the expansion is expected to take place in developing nations. Human population density varies widely around the world, however a majority sleep in Asia. By 2020, hour of the world's population is expected to be living in urban, instead of rural, areas.[157]
It is calculable that only simple fraction of the surface of the planet is suitable for humans to live on—three-quarters is covered by oceans, and 1/2 the acreage is either desert (14%),[158] high mountains (27%),[159] or other less suitable piece of ground. The northmost permanent settlement in the world is *****, on Ellesmere Island in territory, Canada.[160] (82°28′N) The southernmost is that the Amundsen-Scott South Pole Station, in Antarctic continent, virtually exactly at the South Pole. (90°S)
The Earth at nighttime, a composite of DMSP/OLS ground illumination information on a simulated night-time image of the world. This image isn't photographic and plenty of options are brighter than they'd seem to an on the spot observer.

Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctic continent and therefore the odd unclaimed area of Bir Tawil between Egypt and Sudan. As of 2011 there are 203 sovereign states, including the 192 UN member states. additionally, there are 59 dependent territories, and a number of autonomous areas, territories underneath dispute and other entities.[13] historically, Earth has ne'er had a sovereign government with authority over the whole globe, though a number of nation-states have striven for world domination and unsuccessful.[161]
The UN may be a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.[162] it's not, however, a world government. The U.N. serves primarily as a forum for international diplomacy and jurisprudence. when the accord of the membership permits, it provides a mechanism for armed intervention.[163]
The first human to orbit the planet was Yuri Alekseyevich Gagarin on Apr twelve, 1961.[164] In total, regarding 400 people visited outer space and reached Earth orbit as of 2004, and, of these, twelve have walked on the Moon.[165][166][167] unremarkably the sole humans in space are those on the International satellite. The station's crew, presently six people, is usually replaced each six months.[168] The furthest humans have cosmopolitan from Earth is 400,171 km, achieved throughout the 1970 Greek deity 13 mission.[169]

06-28-2014, 12:48 PM
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