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التعليقات (7)
http://en.wikipedia.org/wiki/Earth
اختي السلام عليكم
هذا رابط فيه الكثير من المعلومات
لا تنسي الدعاء لي وللمسلمين
اختي السلام عليكم
هذا رابط فيه الكثير من المعلومات
لا تنسي الدعاء لي وللمسلمين
السلام عليكم فراشات
ابي طلب وان شاء الله تقدرن عليه
اني ابي درس عن Earth and its Neighbours
لاني عجزت وهو مطلوب علي
الرجاء المساعده
تحياتي
ابي طلب وان شاء الله تقدرن عليه
اني ابي درس عن Earth and its Neighbours
لاني عجزت وهو مطلوب علي
الرجاء المساعده
تحياتي
Earth
From Wikipedia, the free encyclopedia
Jump to: navigation , search
This article is about the planet. For other uses, see Earth (disambiguation) .
Earth Famous " Blue Marble " photograph of Earth, taken from Apollo 17
Designations
AdjectiveTerrestrial, Terran, Telluric , Tellurian, Earthly Orbital characteristics
Epoch J2000.0
Aphelion 152,097,701 km
1.0167103335 AU Perihelion 147,098,074 km
0.9832898912 AU Semi-major axis 149,597,887.5 km
1.0000001124 AU Eccentricity 0.016710219 Orbital period 365.256366 days
1.0000175 yr Average orbital speed 29.783 km/s
107,218 km/h Inclination 1آ°34'43.3"
to Invariable plane Longitude of ascending node 348.73936آ° Argument of perihelion 114.20783آ° Satellites 1 (the Moon )Physical characteristics
Mean radius6,371.0 km
Equatorial radius6,378.1 km
Polar radius6,356.8 km
Flattening 0.0033528
Circumference40,075.02 km ( equatorial )
40,007.86 km ( meridional )
40,041.47 km (mean) Surface area 510,072,000 kmآ²
148,940,000 kmآ² land (29.2 %)
361,132,000 kmآ² water (70.8 %) Volume 1.0832073أ—1012 kmآ³ Mass 5.9736أ—1024 kg
Mean density 5.5153 g/cmآ³ Equatorial surface gravity 9.780327 m/sآ²
0.99732 g Escape velocity 11.186 km/s
Sidereal rotation
period 0.99726968 d
23 h 56 m 4.100 s Equatorial rotation velocity465.11 m/s Axial tilt 23.439281آ° Albedo 0.367
Surface temp.
Kelvin
Celsius minmeanmax184 K287 K331 K−89 آ°C14 آ°C57.7 آ°CAtmosphere
Surface pressure 101.3 kPa ( MSL )Composition78.08% Nitrogen (N2)
20.95% Oxygen (O2)
0.93% Argon
0.038% Carbon dioxide
About 1% water vapor (varies with climate )
Earth (pronounced /ةثگخ¸/ ( help آ· info ) )
is the third planet from the Sun . Earth is the largest of the terrestrial planets in the Solar System in diameter , mass and density . It is also referred to as the World and Terra .
Home to millions of species ,
including humans , Earth is the only place in the universe where life is known to exist. The planet formed 4.54 billion years ago,
and life appeared on its surface within a billion years. Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field , blocks harmful radiation, permitting life on land.
The physical properties of the Earth, as well as its geological history and orbit, allowed life to persist during this period. The world is expected to continue supporting life for another 1.5 billion years, after which the rising luminosity of the Sun will eliminate the biosphere .
Earth's outer surface is divided into several rigid segments, or tectonic plates , that gradually migrate across the surface over periods of many millions of years . About 71% of the surface is covered with salt-water oceans , the remainder consisting of continents and islands ; liquid water , necessary for all known life, is not known to exist on any other planet's surface.
Earth's interior remains active, with a thick layer of relatively solid mantle , a liquid outer core that generates a magnetic field, and a solid iron inner core .
Earth interacts with other objects in outer space , including the Sun and the Moon . At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year , which is equal to 365.26 solar days .
The Earth's axis of rotation is tilted 23.4آ° away from the perpendicular to its orbital plane ,
producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite , the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides , stabilizes the axial tilt and gradually slows the planet's rotation. A cometary bombardment during the early history of the planet played a role in the formation of the oceans.
Later, asteroid impacts caused significant changes to the surface environment.
Both the mineral resources of the planet, as well as the products of the biosphere , contribute resources that are used to support a global human population. The inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth, and a modern perspective of the world as an integrated environment that requires stewardship. Humans first left the planet in 1961, when Yuri Gagarin reached outer space .
Chronology
Main article: History of the Earth
See also: Geological history of Earth Scientists have been able to reconstruct detailed information about the planet's past. About 4.54 billion years ago (within an uncertainty of 1%),
the Earth and the other planets in the Solar System formed out of the solar nebula —a disk-shaped mass of dust and gas left over from the formation of the Sun. This assembly of the Earth through accretion was largely completed within 10–20 million years.
Initially molten , the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterward, possibly as the result of a Mars-sized object (sometimes called Theia ) with about 10% of the Earth's mass
impacting the Earth in a glancing blow.
Some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.
Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor , augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans .
Beginning with almost no dry land, the total amount of surface lying above the oceans has steadily increased. During the past two billion years, for example, the total size of the continents has doubled.
On time scales lasting hundreds of millions of years, the surface continually reshaped itself as continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent . Roughly 750 million years ago ( mya ), one the earliest known supercontinents, Rodinia , began to break apart. The continents later recombined to form Pannotia , 600–540 mya, then finally Pangaea , which broke apart 180 mya.
Evolution of life
Main article: Evolutionary history of life
Highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed.
The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed in a layer of ozone (a form of molecular oxygen
) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes .
True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer , life colonized the surface of Earth.
Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 mya, during the Neoproterozoic , covered much of the planet in a sheet of ice. This hypothesis has been termed " Snowball Earth ", and is of particular interest because it preceded the Cambrian explosion , when multicellular life forms began to proliferate.
Following the Cambrian explosion, about 535 mya, there have been five mass extinctions .
The last extinction event was 65 mya, 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 has diversified, and several mya, an African ape-like animal gained the ability to stand upright.
This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,
affecting both the nature and quantity of other life forms.
The present pattern of ice ages began about 40 mya and then intensified during the Pleistocene about 3 mya. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago.
Future
See also: Risks to civilization, humans and planet Earth
The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium ash at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10 percent over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.
Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans.
The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle , reducing its concentration to the lethal levels for plants (10 ppm for C4 photosynthesis ) in 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.
But even if the Sun were eternal and stable, the continued internal cooling of the Earth would have resulted in a loss of much of its atmosphere and oceans due to reduced volcanism .
After another billion years all surface water will have disappeared
and the mean global temperature will reach 70آ°C.
The Earth is expected to be effectively habitable for about another 500 million years.
The Sun, as part of its evolution , will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present size, roughly 1 AU (150,000,000 km ).
Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. Therefore, the planet is expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life will be destroyed because of the Sun's increased luminosity.
However, a more recent simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be destroyed.
Composition and structure
Main article: Earth science
Further information: Earth physical characteristics tables Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter . It is the largest of the four solar terrestrial planets, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity , the strongest magnetic field, and fastest rotation.
It also is the only terrestrial planet with active plate tectonics .
Shape
Main article: Figure of the Earth
Size comparison of inner planets (left to right): Mercury , Venus , Earth, and Mars
The Earth's shape is very close to an oblate spheroid —a rounded shape with a bulge around the equator —although the precise shape (the geoid ) varies from this by up to 100 meters.
The average diameter of the reference spheroid is about 12,742 km. More approximately, this distance is 40,000 km/ د€ because the meter was originally defined as 1/10,000,000 of the distance from the equator to the north pole through Paris , France.
The rotation of the Earth creates the equatorial bulge so that the diameter at the equator is 43 km larger than the pole to pole diameter.
The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level ) and the Mariana Trench (10,911 m below local sea level). Hence compared to a perfect ellipsoid , the Earth has a tolerance of about one part in about 584, or 0.17%, which is less than the 0.22% tolerance allowed in billiard balls .
Because of the bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador .
F. W. Clarke's Table of Crust OxidesCompoundFormulaComposition silica SiO259.71% alumina Al2O315.41% lime CaO4.90% Magnesia MgO4.36% sodium oxide Na2O3.55% iron(II) oxide FeO3.52% potassium oxide K2O2.80% iron(III) oxide Fe2O32.63% water H2O1.52% titanium dioxide TiO20.60% phosphorus pentoxide P2O50.22%Total99.22%
Chemical composition
See also: Abundance of elements on Earth The mass of the Earth is approximately 5.98أ—1024 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation , the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.
The geochemist F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99.22% were composed of 11 oxides (see the table at right.) All the other constituents occur only in very small quantities.
Internal structure
Main article: Structure of the Earth
The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle , a liquid outer core that is much less viscous than the mantle, and a solid inner core . The crust is separated from the mantle by the Mohoroviؤچiؤ‡ discontinuity , and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents.
The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5آ° per year.
Geologic layers of the Earth
Earth cutaway from core to exosphere. Not to scale.Depth
km Component LayerDensity
g/cmآ³ 0–60 Lithosphere
—0–35... Crust
2.2–2.935–60... Upper mantle3.4–4.435–2890 Mantle 3.4–5.6100–700... Asthenosphere —2890–5100 Outer core 9.9–12.25100–6378 Inner core 12.8–13.1
The internal heat of the planet is probably produced by the radioactive decay of potassium-40 , uranium-238 and thorium-232 isotopes . All three have half-life decay periods of more than a billion years.
At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa .
A portion of the core's thermal energy is transported toward the crust by Mantle plumes ; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts .
Tectonic plates
Main article: Plate tectonics
According to plate tectonics theory, the outermost part of the Earth's interior is made up of two layers: the lithosphere , comprising the crust , and the solidified uppermost part of the mantle . Below the lithosphere lies the asthenosphere , which forms the inner part of the upper mantle. The asthenosphere behaves like a superheated material that is in a semi-fluidic, plastic-like state.
The lithosphere essentially floats on the asthenosphere and is broken up into what are called tectonic plates . These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent , divergent and transform . The last occurs where two plates move laterally relative to each other, creating a strike-slip fault . Earthquakes , volcanic activity, mountain-building , and oceanic trench formation can occur along these plate boundaries.
Earth's main plates
A map illustrating the Earth's major plates.Plate nameArea
106 kmآ² African Plate 61.3 Antarctic Plate 60.9 Australian Plate 47.2 Eurasian Plate 67.8 North American Plate 75.9 South American Plate 43.6 Pacific Plate 103.3
Notable minor plates include the Indian Plate , the Arabian Plate , the Caribbean Plate , the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean . The Australian Plate actually fused with Indian Plate between 50 and 55 million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/yr
and the Pacific Plate moving 52–69 mm/yr. At the other extreme, the slowest-moving plate is the Eurasian Plate , progressing at a typical rate of about 21 mm/yr.
Surface
Main articles: Landform and Extreme points of Earth
The Earth's terrain varies greatly from place to place. About 70.8%
of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes ,
oceanic trenches , submarine canyons , oceanic plateaus and abyssal plains . The remaining 29.2% not covered by water consists of mountains , deserts , plains , plateaus , and other geomorphologies .
The planetary surface undergoes reshaping over geological time periods due to the effects of tectonics and erosion . The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation , thermal cycles, and chemical effects. Glaciation , coastal erosion , the build-up of coral reefs , and large meteorite impacts
also act to reshape the landscape.
Present day Earth altimetry and bathymetry . Data from the National Geophysical Data Center 's TerrainBase Digital Terrain Model .
As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges. At the same time, upwellings of mantle material create a divergent boundary along mid-ocean ridges . The combination of these processes continually recycles the oceanic crustal material. Most of the ocean floor is less than 100 million years in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about 200 million years. By comparison, the oldest fossils found on land
From Wikipedia, the free encyclopedia
Jump to: navigation , search
This article is about the planet. For other uses, see Earth (disambiguation) .
Earth Famous " Blue Marble " photograph of Earth, taken from Apollo 17
Designations
AdjectiveTerrestrial, Terran, Telluric , Tellurian, Earthly Orbital characteristics
Epoch J2000.0
Aphelion 152,097,701 km
1.0167103335 AU Perihelion 147,098,074 km
0.9832898912 AU Semi-major axis 149,597,887.5 km
1.0000001124 AU Eccentricity 0.016710219 Orbital period 365.256366 days
1.0000175 yr Average orbital speed 29.783 km/s
107,218 km/h Inclination 1آ°34'43.3"
to Invariable plane Longitude of ascending node 348.73936آ° Argument of perihelion 114.20783آ° Satellites 1 (the Moon )Physical characteristics
Mean radius6,371.0 km
Equatorial radius6,378.1 km
Polar radius6,356.8 km
Flattening 0.0033528
Circumference40,075.02 km ( equatorial )
40,007.86 km ( meridional )
40,041.47 km (mean) Surface area 510,072,000 kmآ²
148,940,000 kmآ² land (29.2 %)
361,132,000 kmآ² water (70.8 %) Volume 1.0832073أ—1012 kmآ³ Mass 5.9736أ—1024 kg
Mean density 5.5153 g/cmآ³ Equatorial surface gravity 9.780327 m/sآ²
0.99732 g Escape velocity 11.186 km/s
Sidereal rotation
period 0.99726968 d
23 h 56 m 4.100 s Equatorial rotation velocity465.11 m/s Axial tilt 23.439281آ° Albedo 0.367
Surface temp.
Kelvin
Celsius minmeanmax184 K287 K331 K−89 آ°C14 آ°C57.7 آ°CAtmosphere
Surface pressure 101.3 kPa ( MSL )Composition78.08% Nitrogen (N2)
20.95% Oxygen (O2)
0.93% Argon
0.038% Carbon dioxide
About 1% water vapor (varies with climate )
Earth (pronounced /ةثگخ¸/ ( help آ· info ) )
is the third planet from the Sun . Earth is the largest of the terrestrial planets in the Solar System in diameter , mass and density . It is also referred to as the World and Terra .
Home to millions of species ,
including humans , Earth is the only place in the universe where life is known to exist. The planet formed 4.54 billion years ago,
and life appeared on its surface within a billion years. Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field , blocks harmful radiation, permitting life on land.
The physical properties of the Earth, as well as its geological history and orbit, allowed life to persist during this period. The world is expected to continue supporting life for another 1.5 billion years, after which the rising luminosity of the Sun will eliminate the biosphere .
Earth's outer surface is divided into several rigid segments, or tectonic plates , that gradually migrate across the surface over periods of many millions of years . About 71% of the surface is covered with salt-water oceans , the remainder consisting of continents and islands ; liquid water , necessary for all known life, is not known to exist on any other planet's surface.
Earth's interior remains active, with a thick layer of relatively solid mantle , a liquid outer core that generates a magnetic field, and a solid iron inner core .
Earth interacts with other objects in outer space , including the Sun and the Moon . At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year , which is equal to 365.26 solar days .
The Earth's axis of rotation is tilted 23.4آ° away from the perpendicular to its orbital plane ,
producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite , the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides , stabilizes the axial tilt and gradually slows the planet's rotation. A cometary bombardment during the early history of the planet played a role in the formation of the oceans.
Later, asteroid impacts caused significant changes to the surface environment.
Both the mineral resources of the planet, as well as the products of the biosphere , contribute resources that are used to support a global human population. The inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth, and a modern perspective of the world as an integrated environment that requires stewardship. Humans first left the planet in 1961, when Yuri Gagarin reached outer space .
Chronology
Main article: History of the Earth
See also: Geological history of Earth Scientists have been able to reconstruct detailed information about the planet's past. About 4.54 billion years ago (within an uncertainty of 1%),
the Earth and the other planets in the Solar System formed out of the solar nebula —a disk-shaped mass of dust and gas left over from the formation of the Sun. This assembly of the Earth through accretion was largely completed within 10–20 million years.
Initially molten , the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterward, possibly as the result of a Mars-sized object (sometimes called Theia ) with about 10% of the Earth's mass
impacting the Earth in a glancing blow.
Some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.
Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor , augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans .
Beginning with almost no dry land, the total amount of surface lying above the oceans has steadily increased. During the past two billion years, for example, the total size of the continents has doubled.
On time scales lasting hundreds of millions of years, the surface continually reshaped itself as continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent . Roughly 750 million years ago ( mya ), one the earliest known supercontinents, Rodinia , began to break apart. The continents later recombined to form Pannotia , 600–540 mya, then finally Pangaea , which broke apart 180 mya.
Evolution of life
Main article: Evolutionary history of life
Highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed.
The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed in a layer of ozone (a form of molecular oxygen
) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes .
True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer , life colonized the surface of Earth.
Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 mya, during the Neoproterozoic , covered much of the planet in a sheet of ice. This hypothesis has been termed " Snowball Earth ", and is of particular interest because it preceded the Cambrian explosion , when multicellular life forms began to proliferate.
Following the Cambrian explosion, about 535 mya, there have been five mass extinctions .
The last extinction event was 65 mya, 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 has diversified, and several mya, an African ape-like animal gained the ability to stand upright.
This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,
affecting both the nature and quantity of other life forms.
The present pattern of ice ages began about 40 mya and then intensified during the Pleistocene about 3 mya. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago.
Future
See also: Risks to civilization, humans and planet Earth
The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium ash at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10 percent over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.
Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans.
The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle , reducing its concentration to the lethal levels for plants (10 ppm for C4 photosynthesis ) in 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.
But even if the Sun were eternal and stable, the continued internal cooling of the Earth would have resulted in a loss of much of its atmosphere and oceans due to reduced volcanism .
After another billion years all surface water will have disappeared
and the mean global temperature will reach 70آ°C.
The Earth is expected to be effectively habitable for about another 500 million years.
The Sun, as part of its evolution , will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present size, roughly 1 AU (150,000,000 km ).
Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. Therefore, the planet is expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life will be destroyed because of the Sun's increased luminosity.
However, a more recent simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be destroyed.
Composition and structure
Main article: Earth science
Further information: Earth physical characteristics tables Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter . It is the largest of the four solar terrestrial planets, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity , the strongest magnetic field, and fastest rotation.
It also is the only terrestrial planet with active plate tectonics .
Shape
Main article: Figure of the Earth
Size comparison of inner planets (left to right): Mercury , Venus , Earth, and Mars
The Earth's shape is very close to an oblate spheroid —a rounded shape with a bulge around the equator —although the precise shape (the geoid ) varies from this by up to 100 meters.
The average diameter of the reference spheroid is about 12,742 km. More approximately, this distance is 40,000 km/ د€ because the meter was originally defined as 1/10,000,000 of the distance from the equator to the north pole through Paris , France.
The rotation of the Earth creates the equatorial bulge so that the diameter at the equator is 43 km larger than the pole to pole diameter.
The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level ) and the Mariana Trench (10,911 m below local sea level). Hence compared to a perfect ellipsoid , the Earth has a tolerance of about one part in about 584, or 0.17%, which is less than the 0.22% tolerance allowed in billiard balls .
Because of the bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador .
F. W. Clarke's Table of Crust OxidesCompoundFormulaComposition silica SiO259.71% alumina Al2O315.41% lime CaO4.90% Magnesia MgO4.36% sodium oxide Na2O3.55% iron(II) oxide FeO3.52% potassium oxide K2O2.80% iron(III) oxide Fe2O32.63% water H2O1.52% titanium dioxide TiO20.60% phosphorus pentoxide P2O50.22%Total99.22%
Chemical composition
See also: Abundance of elements on Earth The mass of the Earth is approximately 5.98أ—1024 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation , the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.
The geochemist F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99.22% were composed of 11 oxides (see the table at right.) All the other constituents occur only in very small quantities.
Internal structure
Main article: Structure of the Earth
The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle , a liquid outer core that is much less viscous than the mantle, and a solid inner core . The crust is separated from the mantle by the Mohoroviؤچiؤ‡ discontinuity , and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents.
The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5آ° per year.
Geologic layers of the Earth
Earth cutaway from core to exosphere. Not to scale.Depth
km Component LayerDensity
g/cmآ³ 0–60 Lithosphere
—0–35... Crust
2.2–2.935–60... Upper mantle3.4–4.435–2890 Mantle 3.4–5.6100–700... Asthenosphere —2890–5100 Outer core 9.9–12.25100–6378 Inner core 12.8–13.1
The internal heat of the planet is probably produced by the radioactive decay of potassium-40 , uranium-238 and thorium-232 isotopes . All three have half-life decay periods of more than a billion years.
At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa .
A portion of the core's thermal energy is transported toward the crust by Mantle plumes ; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts .
Tectonic plates
Main article: Plate tectonics
According to plate tectonics theory, the outermost part of the Earth's interior is made up of two layers: the lithosphere , comprising the crust , and the solidified uppermost part of the mantle . Below the lithosphere lies the asthenosphere , which forms the inner part of the upper mantle. The asthenosphere behaves like a superheated material that is in a semi-fluidic, plastic-like state.
The lithosphere essentially floats on the asthenosphere and is broken up into what are called tectonic plates . These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent , divergent and transform . The last occurs where two plates move laterally relative to each other, creating a strike-slip fault . Earthquakes , volcanic activity, mountain-building , and oceanic trench formation can occur along these plate boundaries.
Earth's main plates
A map illustrating the Earth's major plates.Plate nameArea
106 kmآ² African Plate 61.3 Antarctic Plate 60.9 Australian Plate 47.2 Eurasian Plate 67.8 North American Plate 75.9 South American Plate 43.6 Pacific Plate 103.3
Notable minor plates include the Indian Plate , the Arabian Plate , the Caribbean Plate , the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean . The Australian Plate actually fused with Indian Plate between 50 and 55 million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/yr
and the Pacific Plate moving 52–69 mm/yr. At the other extreme, the slowest-moving plate is the Eurasian Plate , progressing at a typical rate of about 21 mm/yr.
Surface
Main articles: Landform and Extreme points of Earth
The Earth's terrain varies greatly from place to place. About 70.8%
of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes ,
oceanic trenches , submarine canyons , oceanic plateaus and abyssal plains . The remaining 29.2% not covered by water consists of mountains , deserts , plains , plateaus , and other geomorphologies .
The planetary surface undergoes reshaping over geological time periods due to the effects of tectonics and erosion . The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation , thermal cycles, and chemical effects. Glaciation , coastal erosion , the build-up of coral reefs , and large meteorite impacts
also act to reshape the landscape.
Present day Earth altimetry and bathymetry . Data from the National Geophysical Data Center 's TerrainBase Digital Terrain Model .
As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges. At the same time, upwellings of mantle material create a divergent boundary along mid-ocean ridges . The combination of these processes continually recycles the oceanic crustal material. Most of the ocean floor is less than 100 million years in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about 200 million years. By comparison, the oldest fossils found on land
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