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Earth, otherwise known as the world, 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.

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)
29.78 km/s (18.50 mi/s)
(107,200 km/h (66,600 mph))
358.617°
Inclination
Longitude of ascending node
−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
Surface area
  • 510,072,000 km (196,940,000 sq mi)
  •  (148,940,000 km (57,510,000 sq mi) (29.2%) land
  •   361,132,000 km (139,434,000 sq mi) (70.8%) water)
Volume 1.08321×10 km (2.59876×10 cu mi)
Mass 5.97237×10 kg (1.31668×10 lb)
(3.0×10 M)
Mean density
5.514 g/cm (0.1992 lb/cu in)
9.807 m/s (32.18 ft/s)
(g)
0.3307
11.186 km/s (6.951 mi/s)
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. During one orbit around the Sun (one year), Earth rotates about its axis, creating 365.26 days. Earth's axis of rotation is tilted, producing seasonal variations on the planet's surface. Earth has only one moon. 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. Seventy-one percent of Earth's surface is covered with water. 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.

Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7.3 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humanity has developed diverse societies and cultures; politically, the world is divided into about 200 sovereign states.