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Earth

Earth Astronomical symbol of Earth
"The Blue Marble" photograph of Earth, taken by the Apollo 17 mission. The Arabian peninsula, Africa and Madagascar lie in the upper half of the disc, whereas Antarctica is at the bottom.
The Blue Marble photograph of Earth, taken during the Apollo 17 lunar mission in 1972
Orbital characteristics
Epoch J2000
Aphelion
152,100,000 km (94,500,000 mi)
(1.01673 AU) 
Perihelion
147,095,000 km (91,401,000 mi)
(0.9832687 AU) 
149,598,023 km (92,955,902 mi)
(1.000001018 AU) 
Eccentricity 0.0167086
365.256363004 d
(1.00001742096 yr)
Average orbital speed
29.78 km/s (18.50 mi/s)
(107,200 km/h (66,600 mph))
358.617°
Inclination
−11.26064° to J2000 ecliptic
114.20783°
Satellites
Physical characteristics
Mean radius
6,371.0 km (3,958.8 mi)
Equatorial radius
6,378.1 km (3,963.2 mi)
Polar radius
6,356.8 km (3,949.9 mi)
Flattening 0.0033528
1/298.257222101 (ETRS89)
Circumference
  • 510,072,000 km2 (196,940,000 sq mi)
  •  148,940,000 km2 (57,510,000 sq mi) (29.2%) land
  •  361,132,000 km2 (139,434,000 sq mi) (70.8%) water
Volume 1.08321×1012 km3 (2.59876×1011 cu mi)
Mass 5.97237×1024 kg (1.31668×1025 lb)
(3.0×10−6 M)
Mean density
5.514 g/cm3 (0.1992 lb/cu in)
9.807 m/s2 (32.18 ft/s2)
(g)
0.3307
11.186 km/s (6.951 mi/s)
Sidereal rotation period
0.99726968 d
(23h 56m 4.100s)
Equatorial rotation velocity
1,674.4 km/h (1,040.4 mph)
23.4392811°
Albedo
Surface temp. min mean max
Kelvin 184 K 288 K 330 K
Celsius −89.2 °C 15 °C 56.7 °C
Fahrenheit −128.5 °F 59 °F 134 °F
Atmosphere
Surface pressure
101.325 kPa (at MSL)
Composition by volume

Earth, otherwise known as the world, (Greek: Γαῖα Gaia; Latin: Terra) is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets.

According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus an Earth year is about 365.26 days long. Earth's axis of rotation is tilted, producing seasonal variations on the planet's surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earth's orientation on its axis, and gradually slows its rotation.

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water, mostly by its oceans. The remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, and a convecting mantle that drives plate tectonics.


Chemical composition of the crust
Compound Formula Composition
Continental Oceanic
silica SiO2 60.2% 48.6%
alumina Al2O3 15.2% 16.5%
lime CaO 5.5% 12.3%
magnesia MgO 3.1% 6.8%
iron(II) oxide FeO 3.8% 6.2%
sodium oxide Na2O 3.0% 2.6%
potassium oxide K2O 2.8% 0.4%
iron(III) oxide Fe2O3 2.5% 2.3%
water H2O 1.4% 1.1%
carbon dioxide CO2 1.2% 1.4%
titanium dioxide TiO2 0.7% 1.4%
phosphorus pentoxide P2O5 0.2% 0.3%
Total 99.6% 99.9%
Geologic layers of Earth
Earth-cutaway-schematic-english.svg

Earth cutaway from core to exosphere. Not to scale.
Depth
km
Component layer Density
g/cm3
0–60 Lithosphere
0–35 Crust 2.2–2.9
35–60 Upper mantle 3.4–4.4
  35–2890 Mantle 3.4–5.6
100–700 Asthenosphere
2890–5100 Outer core 9.9–12.2
5100–6378 Inner core 12.8–13.1
Present-day major heat-producing isotopes
Isotope Heat release
W/kg isotope
Half-life
years
Mean mantle concentration
kg isotope/kg mantle
Heat release
W/kg mantle
238U 94.6 × 10−6 4.47 × 109 30.8 × 10−9 2.91 × 10−12
235U 569 × 10−6 0.704 × 109 0.22 × 10−9 0.125 × 10−12
232Th 26.4 × 10−6 14.0 × 109 124 × 10−9 3.27 × 10−12
40K 29.2 × 10−6 1.25 × 109 36.9 × 10−9 1.08 × 10−12
Earth's major plates
Shows the extent and boundaries of tectonic plates, with superimposed outlines of the continents they support
Plate name Area
106 km2
103.3
78.0
75.9
67.8
60.9
47.2
43.6
Estimated human land use, 2000
Land use Mha
Cropland 1,510–1,611
Pastures 2,500–3,410
Natural forests 3,143–3,871
Planted forests 126–215
Urban areas 66–351
Unused, productive land 356–445
Characteristics
Full moon as seen from Earth's Northern Hemisphere
Diameter 3,474.8 km
Mass 7.349×1022 kg
Semi-major axis 384,400 km
Orbital period 27 d 7 h 43.7 m

  • 510,072,000 km2 (196,940,000 sq mi)
  •  148,940,000 km2 (57,510,000 sq mi) (29.2%) land
  •  361,132,000 km2 (139,434,000 sq mi) (70.8%) water
  • Proximity to oceans moderates the climate. For example, the Scandinavian peninsula has more moderate climate than similarly northern latitudes of northern Canada.
  • The wind enables this moderating effect. The windward side of a land mass experiences more moderation than the leeward side. In the Northern Hemisphere, the prevailing wind is west-to-east, and western coasts tend to be milder than eastern coasts. This is seen in Eastern North America and Western Europe, where rough continental climates appear on the east coast on parallels with mild climates on the other side of the ocean. In the Southern Hemisphere, the prevailing wind is east-to-west, and the eastern coasts are milder.
  • The distance from the Earth to the Sun varies. The Earth is closest to the Sun (at perihelion) in January, which is summer in the Southern Hemisphere. It is furthest away (at aphelion) in July, which is summer in the Northern Hemisphere, and only 93.55% of the solar radiation from the Sun falls on a given square area of land than at perihelion. Despite this, there are larger land masses in the Northern Hemisphere, which are easier to heat than the seas. Consequently, summers are 2.3 °C (4 °F) warmer in the Northern Hemisphere than in the Southern Hemisphere under similar conditions.
  • The climate is colder at high altitudes than at sea level because of the decreased air density.
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Wikipedia

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