पृथ्वी

नेपाली विकिपीडियाबाट
यसमा जानुहोस्: परिचालन, खोज्नुहोस्
Earth  Astronomical symbol of Earth
A color image of पृथ्वी as seen from Apollo 17
"The Blue Marble" photograph of पृथ्वी,
taken from Apollo 17
Designations
Pronunciation Listeni/ˈɜrθ/
Adjective earthly, tellurian, telluric, terran, terrestrial.
Epoch J2000.0[note १]
Aphelion 152,098,232 km
1.01671388 AU[note २]
Perihelion 147,098,290 km
0.98329134 AU[note २]
Semi-major axis 149,598,261 km
1.00000261 AU[१]
Eccentricity 0.01671123[१]
परिभ्रमण अवधि 365.256363004 days[२]
1.000017421 yr
परिभ्रमण गति 29.78 km/s[३]
107,200 km/h
Mean anomaly 357.51716°[३]
Inclination 7.155° to Sun's equator
1.57869°[४] to invariable plane
Longitude of ascending node 348.73936°[३][note ३]
Argument of perihelion 114.20783°[३][note ४]
उपग्रह 1 (the Moon)
Physical characteristics
औशत अर्धब्यास 6,371.0 km[५]
भूमध्यरेखीय अर्धब्यास 6,378.1 km[६][७]
ध्रुवीय अर्धब्यास 6,356.8 km[८]
Flattening 0.0033528[९]
परिमिति 40,075.017 km (equatorial)[७]
40,008.00 km (meridional)[१०]
सतहको क्षेत्रफल 510,072,000 km2[११][१२][note ५]

148,940,000 km2 land (29.2 %)

361,132,000 km2 water (70.8 %)
आयतन 1.08321×10१२ km3[३]
पिण्ड 5.9736×10२४ kg[३]
औशत घनत्व 5.515 g/cm3[३]
Equatorial surface gravity 9.780327 m/s2[१३]
0.99732 g
Escape velocity 11.186 km/s[३]
परिक्रमण अवधि 0.99726968 d[१४]
23h 56m 4.100s
Equatorial rotation velocity १,६७४.४ km/h (४६५.१ m/s)[१५]
अक्षको झुकाव 23°26'21".4119[२]
Albedo 0.367 (geometric)[३]
0.306 (Bond)[३]
Surface temp.
   Kelvin
   Celsius
min mean max
184 K[१६] 287.2 K[१७] 331 K[१८]
-89.2 °C 14 °C 57.8 °C
Atmosphere
वायुमण्डलीय चाप 101.325 kPa (MSL)
वायुमण्डलीय तत्वहरू 78.08% nitrogen (N2)[३]
20.95% oxygen (O2)
0.93% argon
0.038% carbon dioxide
About 1% water vapor (varies with climate)

पृथ्वी, (अङ्‍ग्रेजी the Earth or Terra), सौर्यमण्डलको तेस्रो ग्रह हो। It is the largest of the solar system's terrestrial planets, र the only planetary body that modern science confirms as harboring life. यो ग्रह करिव ४.५७ अर्ब (४.५७×१०) बर्ष अगाडि उतपन्न भएको हो। त्यसको केही पछि यसले एकमात्र प्राकृतिक उपग्रह, चन्द्रमा, प्राप्त गर्‍यो। यसका प्रमूख चेतनशिल प्राणी मानव हुन। (Homo sapiens sapiens).

Its symbol consists of a circled cross, representing a meridian र the equator; a variant puts the cross atop the circle (Unicode: ⊕ or ♁).

Physical characteristics

Shape

पृथ्वीको आकृति केही चेप्टो अण्डाकार रहेको छ, यसको व्यास करिब् १२,७४२ किमि छ। यसको अधिकतम झुकावका कारण पृथ्वीमा सबैभन्दा अग्लो स्थान (८,८४८ मिटर उचाई भएकोसगरमाथाको चुचुरो ) र सबैभन्दा होचो स्थान (समुन्द्री सतह भन्दा १०,९११ मिटर मुनी मारियाना ट्रेन्च) रहेको छ। Thus the पृथ्वी is an oblate spheroid within a tolerance of one part in about 584, or 0.17 %. The mass of the पृथ्वी is approximately 6,000 yottagrams (6 x 1024 kg).

Structure

The interior of पृथ्वी, like that of the other terrestrial planets, is chemically divided into an outer siliceous solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, र a solid inner core. The liquid outer core gives rise to a weak magnetic field due to the convection of its electrically conductive material.

New material constantly finds its way to the surface through volcanoes र cracks in the ocean floors (see seafloor spreading). Much of पृथ्वीको crust is less than 100 million (1×108) years old; the very oldest parts of the crust are as much as 4.4 billion (4.4×109) years old [१].

Taken as a whole, the पृथ्वीको composition by mass [२] is:

अक्सिजन: २८ .२ %
फलाम: ३४ .१ %
सिलिकन: १७ .२ %
म्यागनेसियम: १५ .९ %
निकेल: .६ %
क्यालसियम: .६ %
सिलाबर: .५ %
सल्फर: .७० %
सोडियम: .२५ %
टाइटेनियम: .०७१ %
पोटासियम: .०१९  %
अरु पदार्य:     .५३ %

Interior

Interior heat

ढाँचा:Editnote The interior पृथ्वीको reaches temperatures of 5270 kelvins. The planet's internal heat was originally generated during its accretion (see gravitational binding energy), र since then additional heat has continued to be generated by the decay of radioactive elements such as uranium, thorium, र potassium. The heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the Sun.

Structure

Earth's composition (by depth below surface):

  • 0 to 60 km - Lithosphere (locally varies 5–200 km)
    • 0 to 35 km - Crust (locally varies 5–70 km)
  • 35 to 2890 km - Mantle
  • 2890 to 5100 km - Outer Core
  • 5100 to 6378 km - Inner Core

The core

पृथ्वीको औशत् घनत्व ५,५१५kg/m3 छ त्यसैले यो सौर्य परिवारको सबैभन्दा बढी घनत्व भएको ग्रह हो। पृथ्वीको सतहमा रहेका पदार्थहरूको घनत्व करीब् ३,००० kg/m3, मात्र हुन्छ यसले पृथ्वीको केन्द्रमा अत्याधिक् घनत्व भएका पदार्थहरू पाइन्छन् भन्ने कुरालाई पुष्टी गर्छ। In its earliest stages, about 4.5 billion (4.5×109) years ago, melting would have caused denser substances to sink towards the center in a process called planetary differentiation, while less dense materials would have migrated to the crust. As a result, the core is largely composed of iron (80%), along with nickel र silicon; while other dense elements, such as lead र uranium, are either too rare to be significant or tend to bind to lighter elements र thus remain in the crust (see: felsic materials).

The core is divided into two parts, a solid inner core with a radius of ~1250 km र a liquid outer core extending beyond it to a radius of ~3500 km. The inner core is generally believed to be solid र composed primarily of iron र some nickel. Some have argued that the inner core may be in the form of a single iron crystal. The outer core surrounds the inner core र is believed to be composed of liquid iron mixed with liquid nickel र trace amounts of lighter elements. It is generally believed that convection in the outer core, combined with stirring caused by the Earth's rotation (see: Coriolis forces), gives rise to the Earth's magnetic field through a process known as the dynamo theory. The solid inner core is too hot to hold a permanent magnetic field (see: Curie temperature) but probably acts to stabilise the magnetic field generated by the liquid outer core.

Recent evidence has suggested that the inner core पृथ्वीको may rotate slightly faster than the rest of the planet, by ~2° per year (Comins DEU-p.82).

Earth cutaway from core to exosphere. Partially to scale.

Mantle

Earth's mantle extends to a depth of 2890 km. The pressure, at the bottom of the mantle, is ~140 GPa (1.4 Matm). It is largely composed of substances rich in iron र magnesium. The melting point of a substance depends on the pressure it is under. As there is intense र increasing pressure as one travels deeper into the mantle, the lower part of this region is thought solid while the upper mantle is plastic (semi-molten). The viscosity of the upper mantle ranges between 1021 र 1024 Pa·s, depending on depth [३]. Thus, the upper mantle can only flow very slowly.

Why is the inner core thought solid, the outer core thought liquid, र the mantle solid/plastic? The melting points of iron rich substances are higher than pure iron. The core is composed almost entirely of pure iron, while iron rich substances are more common वाहिर the core. So, surface iron-substances are solid, upper mantle iron-substances are semi-molten (as it is hot र they are under relatively little pressure), lower mantle iron-substances are solid (as they are under tremendous pressure), outer core pure iron is liquid as it has a very low melting point (despite enormous pressure), र the inner core is solid due to the overwhelming pressure found at the center of the planet.

Crust

The crust ranges from 5 to 70 km in depth. The thin parts are oceanic crust composed of dense (mafic) iron magnesium silicate rocks र underlie the ocean basins. The thicker crust is continental crust which is less dense र composed of (felsic) sodium potassium aluminium silicate rocks. The crust-mantle boundary occurs as two physically different events. Firstly, there is a discontinuity in the seismic velocity which is known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below). The second event is a chemical discontinuity between ultramafic cumulates र tectonized harzburgites which has been observed from deep parts of the oceanic crust that have been obducted into the continental crust र preseved as ophiolite sequences.

Biosphere

अहिले सम्मको अध्ययन तथा अनुसन्धान् अनुसार पृथ्वी प्राणी सहितको एक मात्र ग्रह हो। The planet's lifeforms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion (3.5×109) years ago. The biosphere is divided into a number of biomes, inhabited by broadly similar florafauna. On land, biomes are separated primarily by latitude. Terrestrial biomes lying within the ArcticAntarctic Circles are relatively barren of plantanimal life, while most of the more populous biomes lie near the Equator.

Atmosphere

Earth has a relatively thick atmosphere composed of 78% nitrogen, 21% oxygen, र 1% argon, plus traces of other gases including carbon dioxidewater vapor. The atmosphere acts as a buffer between Earth र the Sun. The Earth's atmospheric composition is unstable र is maintained by the biosphere. Namely, the large amount of free diatomic oxygen is maintained through solar energy by the Earth's plants, र without the plants supplying it, the oxygen in the atmosphere will over geological timescales combine with material from the surface of the Earth. Free oxygen in the atmosphere is a signature of life.

The layers, troposphere, stratosphere, mesosphere, thermosphere, र the exosphere, vary around the globe र in response to seasonal changes.

The total mass of the atmosphere is about 5.1 × 1018 kg, ca. 0.9 ppm of the Earth's total mass.

Hydrosphere

चित्र:Earth satellite plane.jpg
A Plate Carrée Projection of a composite satellite image of Earth

पृथ्वी मात्र यस्तो गह्र हो सौर्यमण्डलको जस्मा तरल water पाइन्छ।पानी covers 71% of Earth's surface (97% of it being sea पानी र 3% fresh water [४]) र divides it into ५ oceans र seven continents. Earth's solar orbit, vulcanism, gravity, greenhouse effect, magnetic field र oxygen-rich atmosphere seem to combine to make पृथ्वी a पानी planet.

Earth is actually beyond the outer edge of the orbits which would be warm enough to form liquid पानी. Without some form of a greenhouse effect, Earth's पानी would freeze. Paleontological evidence indicates that at one point after निलो-हरियो bacteria (Cyanobacteria) had colonized the oceans, the greenhouse effect failed, र Earth's oceans may have completely frozen over for १० देखि १०० million बर्ष in what is called a snowball पृथ्वी event.

On अर्को planets, such as Venus, gaseous पानी is destroyed (cracked) by solar ultraviolet radiation, र the hydrogen is ionized र blown away by the solar wind. This effect is slow, but inexorable. This is one hypothesis explaining why Venus has no water. Without hydrogen, the oxygen interacts with the surface र is bound up in solid minerals.

In the पृथ्वीको atmosphere, a tenuous layer of ozone within the stratosphere absorbs most of this energetic ultraviolet radiation high in the atmosphere, reducing the cracking effect. The ozone, too, can only be produced in an atmosphere with a large amount of free diatomic oxygen, र so also is dependent on the biosphere (plants). The magnetosphere also shields the ionosphere from direct scouring by the solar wind.

Finally, vulcanism continuously emits पानी vapor from the interior. Earth's plate tectonics recycle carbon र पानी as limestone rocks are subducted into the mantle र volcanically released as gaseous carbon dioxide र steam. It is estimated that the minerals in the mantle may contain as much as १० times the पानी as in all of the current oceans, though most of this trapped पानी will never be released.

The जम्मा mass of the hydrosphere is about 1.4 × 1021 kg, ca. 0.023 % of the Earth's total mass.

Earth in the Solar System

It takes Earth 23 hours, 56 minutes र 4.09 seconds (1 sidereal day) to rotate around the axis connecting the north pole र the south pole. Thus from Earth the main apparent motion of celestial bodies in the sky (except meteors which are within the atmosphere र low orbiting satellites) is the movement to the west at a rate of 15 °/h = 15'/min, i.e. a Sun or Moon diameter every two minutes.

Earth orbits the Sun every 365.2564 mean solar days (1 sidereal year). Thus from Earth this gives an apparent movement of the Sun with respect to the stars at a rate of ca. 1 °/day, i.e. a Sun or Moon diameter every 12 hours eastward.

The orbital speed of the Earth averages about 30 km/s, which is enough to cover one Earth diameter (~12,700 km) in 7 minutes, र one distance to the Moon (384,000 km) in 4 hours.

Earth has one natural satellite, the Moon, which orbits around Earth every 27 1/3 days. Thus from Earth this gives an apparent movement of the Moon with respect to the Sun र the stars at a rate of roughly 12 °/day, i.e. a Moon diameter every hour eastward.

Viewed from Earth's north pole, the motion of Earth, its moon र their axial rotations are all counterclockwise.

The orbital र axial planes are not precisely aligned: Earth's axis is tilted some 23.5 degrees against the Earth-Sun plane (which causes the seasons), र the Earth-Moon plane is tilted about 5 degrees against the Earth-Sun plane (otherwise there would be an eclipse every month).

The Hill sphere (sphere of influence) of the Earth is about 1.5 Gm (930 thousand miles) in radius, within which one natural satellite (the Moon) comfortably orbits.

In an inertial reference frame, the Earth's axis undergoes a slow precessional motion with a period of some 25,800 years, as well as a nutation with a main period of 18.6 years. These motions are caused by the differential attraction of Sun र Moon on the equatorial bulge due to the Earth's oblateness. In a reference frame attached to the solid body of the Earth, its rotation is also slightly irregular due to polar motion. The polar motion is quasi-periodic, containing an annual component र a component with a 14 month period called the Chandler wobble. Also the rotational velocity varies, a phenomenon known as length of day variation.

The Moon

Name Diameter (km) Mass (kg) Semi-major axis (km) Orbital period
Luna 3,474.8 7.349 × 1022 384,400 27 Days, 7 hours, 43.7 minutes

Luna, or simply 'the Moon', is a relatively large terrestrial planet-like satellite, about one quarter of Earth's diameter. The natural satellites orbiting other planets are called "moons", after Earth's Moon.

The gravitational attraction between the Earth र Moon cause the tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the Earth. As a result it always presents the same face to the planet.

As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases: the dark part of the face is separated from the light part by the solar terminator.

The Moon may enable life by moderating the weather. Paleontological evidence र computer simulations show that Earth's axial tilt is stabilised by tidal interactions with the Moon. Without this stabilization against the torques applied by the Sun र planets to the Earth's equatorial bulge, some theorists believe that the rotational axis might be chaotically unstable, as it appears to be with Mars. If Earth's axis of rotation were to approach the plane of the ecliptic, extremely severe weather could result as this would make seaonal differences extreme. One pole would be pointed directly toward the Sun during summer र directly away during winter. Planetary scientists who have studied the effect claim that this might kill all large animal र higher plant life. This remains a controversial subject, however, र further studies of Mars —which shares Earth's rotation periodaxial tilt, but not its large moon or liquid core— may provide additional information.

The Moon is just far enough away to have, when seen from Earth, very nearly the same apparent angular size as the Sun (the Sun is 400 times larger, but the Moon is 400 times closer). This allows total eclipses as well as annular eclipses to occur on Earth. Here is a diagram showing the relative sizes of the Earth र the Moon र the distance between the two (click to enlarge):

Earth र Moon to scale (click to enlarge)

The Moon's origin is unknown, but one popular hypothesis states that it was formed from the collision of a Mars-sized protoplanet with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron र volatile elements. See Giant impact theory.

Earth also has at least one known co-orbital asteroid, 3753 Cruithne.

Geography

Physical map of the Earth (Medium) (Large 2 MB)

Map references:

Time Zones, Coordinates.

Biggest geographic subdivision

Continents, Oceans

Area:

  • total: 510.073 million km2
  • land: 148.94 million km2
  • water: 361.132 million km2
  • note: 70.8 % of the world's surface is covered by water, 29.2 % is exposed land

Land boundaries: the land boundaries in the world total 251,480 km (not counting shared boundaries twice)

Coastline: 356,000 km

Maritime claims: see United Nations Convention on the Law of the Sea

  • contiguous zone: 24 nautical miles (44.4 km) claimed by most, but can vary
  • continental shelf: 200 m depth claimed by most or to depth of exploitation; others claim 200 nautical miles (370.4 km) or to the edge of the continental margin
  • exclusive fishing zone: 200 nautical miles (370.4 km) claimed by most, but can vary
  • exclusive economic zone: 200 nautical miles (370.4 km) claimed by most, but can vary
  • territorial sea: 12 nautical miles (22.2 km) claimed by most, but can vary
  • Note: boundary situations with neighboring states prevent many countries from extending their fishing or economic zones to a full 200 nautical miles (370.4 km)
  • 43 nations र other areas are completely landlocked (see list of landlocked countries)

Climate

Two large areas of polar climates separated by two rather narrow temperate zones from a wide equatorial band of tropical to subtropical climates. Precipitation patterns vary widely, ranging from several metres of water per year to less than a millimetre.

Terrain

Elevation extremes: (measured relative to sea level)

Natural resources

Some of these resources, such as mineral fuels, are difficult to replenish on a short time scale, called non-renewable resources. The exploitation of non-renewable resources by human civilization has become a subject of significant controversy in modern environmentalism movements.

Land use

  • arable land: 10 %
  • permanent crops: 1 %
  • permanent pastures: 26 %
  • forests र woodland: 32 %
  • urban areas: 1.5 %
  • other: 30 % (1993 est.)

Irrigated land: 2,481,250 km2 (1993 est.)

Natural hazards

Large areas are subject to extreme weather such as (tropical cyclones), hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, floods, droughts, र other calamities र disasters.

Environment - current issues

Large areas are subject to overpopulation, industrial disasters such as pollution of the air र water, acid rain र toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, र introduction of invasive species.

Long term climate alteration due to enhancement of the greenhouse effect by human industrial carbon dioxide emissions is an increasing concern, the focus of intense study र debate.

Human population

Earth at night, composite of pictures taken between October 1994 र March 1995.

On February 25, 2005 the United Nations Population Division issued revised estimates र projected that the world's population will reach 7 billion by 2013 र swell to 9.1 billion in 2050. Most of the growth is expected to take place in developing nations.

Nearly all humans currently reside on Earth: 6,411,000,000 inhabitants (January 5 2005 est.)

Two humans are presently in orbit around Earth on board the International Space Station. The station crew is replaced with new personnel every six months. During the exchange there are more, र sometimes others are also traveling briefly above the atmosphere.

In total, about 400 people have been वाहिर Earth (in space) as of 2004. Most of them have reported a heightened understanding of its value र importance, reverence for human life र amazement at its beauty, not usually achieved by those living on the surface.

See also space colonization.


  1. REDIRECT Human#Society_and_culture  

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The northernmost settlement in the world is Alert, Ellesmere Island, Canada. The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole.

Age structure:

  • 0 to 14 years: 1,819,000,000 (29.9 %)
    • male: 932,800,000 (15.4 %)
    • female: 886,000,000 (14.6 %)
  • 15 to 64 years: 3,841,000,000 (63.2 %)
    • male: 1,942,000,000 (32.0 %)
    • female: 1,898,000,000 (31.2 %)
  • 65 years र over: 419,100,000 (6.9 %)
    • male: 184,100,000 (3.0 %)
    • female: 235,000,000 (3.9 %) (2000 est.)

Population growth rate: 1.14% (2004 est.); 73 mln/year (200,000/day); 1 in 32,000 per day

Birth rate: 22 births/1,000 population (2000 est.); 140 mln/year; 1 in 17,000 per day

Death rate: 9 deaths/1,000 population (2000 est.); 60 mln/year; 1 in 41,000 per day

Sex ratio:

  • at birth: 1.05 male(s)/female
  • under 15 years: 1.05 male(s)/female
  • 15 to 64 years: 1.02 male(s)/female
  • 65 years र over: 0.78 male(s)/female
  • total population: 1.01 male(s)/female (2000 est.)

Infant mortality rate: 54 deaths/1,000 live births (2000 est.)

Life expectancy at birth:

  • total population: 64 years
  • male: 62 years
  • female: 65 years (2000 est.)

Total fertility rate: 2.8 children born/woman (2000 est.)

Government

Earth does not presently have a sovereign government with planetwide authority. Independent sovereign nations claim all of the land surface except Antarctica. There is a worldwide general international organization, the United Nations. The United Nations is primarily an international discussion forum with only limited ability to pass र enforce laws.

Administrative divisions: 267 nations, dependent areas, other, र miscellaneous entries

Descriptions पृथ्वीको

Earth has often been personified as a deity, in particular a goddess. See GaiaMother Earth. In Norse mythology, the earth goddess Jord was the mother of Thor र the daughter of Annar.

Earth has also been described as a massive spaceship, with a life support system that requires maintenance. See Spaceship Earth.

Since Earth is rather large, it is not immediately obvious to the naked eye viewing from the surface that it is an oblate spheroid, bulging slightly at the equator र slightly flattened at the poles. In the past there were varying levels of belief in a flat Earth because of this. Prior to the introduction of space flight, this belief was countered with deductions based on observations of the secondary effects of the earth's shape र parallels drawn with the shape of other planets.

A photo taken पृथ्वीको by Voyager 1 inspired Carl Sagan to describe the planet as a "Pale Blue Dot".

In science fiction, Earth is frequently the capital or a major administrative center of a hypothetical galactic government (especially when that galactic सरकार is postulated to be human-dominated), often a representative federal republic, though empiresdictatorships are definitely not unseen. Notable examples include Star TrekBabylon 5. However, in other science fiction, people in the future no longer know what planet they originally came from (for example, Battlestar GalacticaThe Foundation Series).

The Hitchhiker's Guide to the Galaxy, a book series by Douglas Adams, describes Earth as "Harmless" but the statement is revised in the book र later described as "Mostly Harmless". In the same series, Earth is said to be a supercomputer built by highly advanced pan-dimensional beings (Mice) to find out what the question that The Ultimate Answer to Life, the Universe, र Everything answers actually is.

See also

References

External links


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