Earth

Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth’s surface is land consisting of continents and islands. The remaining 70.8% is covered with water, mostly by oceans, seas, gulfs, and other salt-water bodies, but also by lakes, rivers, and other freshwater, which together constitute the hydrosphere. Much of Earth’s polar regions are covered in ice. Earth’s outer layer is divided into several rigid tectonic plates[list] that migrate across the surface over many millions of years, while its interior remains active with a solid iron inner core, a liquid outer core that generates Earth’s magnetic field, and a convective mantle that drives plate tectonics.

Third planet from the Sun in the Solar System
This article is about the planet. For its human aspects, see World. For other uses, see Earth (disambiguation) and Planet Earth (disambiguation).

Earth

The Blue Marble, the most widely used photograph of Earth,[1][2] taken by the Apollo 17 mission in 1972
Designations
Gaia, Terra, Tellus, the world, the globe
Adjectives Earthly, terrestrial, terran, tellurian
Orbital characteristics
EpochJ2000[n 1]
Aphelion 152100000 km (94500000 mi)[n 2]
Perihelion 147095000 km (91401000 mi)[n 2]
149598023 km (92955902 mi)[3]
Eccentricity 0.0167086[3]
365.256363004 d[4]
(31558.1497635 ks)
29.78 km/s[5]
(107200 km/h; 66600 mph)
358.617°
Inclination
−11.26064°[5] to J2000 ecliptic
2022-Jan-04[7]
114.20783°[5]
Satellites
Physical characteristics
Mean radius
6371.0 km (3958.8 mi)[9]
Equatorial radius
6378.137 km (3963.191 mi)[10][11]
Polar radius
6356.752 km (3949.903 mi)[12]
Flattening 1/298.257222101 (ETRS89)[13]
Circumference
  • 510065623 km2(196937438 sq mi)[15][n 5]
  • 148940000 km2 land (57510000 sq mi)
  • 361132000 km2 water (139434000 sq mi)
Volume 1.08321×1012 km3(2.59876×1011 cu mi)[5]
Mass 5.97237×1024 kg(1.31668×1025 lb)[16]
(3.0×10−6 M)
Mean density
5.514 g/cm3(0.1992 lb/cu in)[5]
9.80665 m/s2(1 g; 32.1740 ft/s2)[17]
0.3307[18]
11.186 km/s[5](40270 km/h; 25020 mph)
1.0 d
(24h 00m 00s) average synodic rotation period (solar day)
0.99726968 d[19]
(23h 56m 4.100s)
Equatorial rotation velocity
0.4651 km/s[20]
(1674.4 km/h; 1040.4 mph)
23.4392811°[4]
Albedo
Surface temp. min mean max
Celsius −89.2 °C[21] 14 °C (1961–90)[22] 56.7 °C[23]
Fahrenheit −128.5 °F 57.2 °F (1961–90) 134.0 °F
Surface equivalent doserate 0.274 μSv/h[24]
Atmosphere
Surface pressure
101.325 kPa (at MSL)
Composition by volume
  • 78.08% nitrogen (

    N2; dry air)[5]

  • 20.95% oxygen (O2)
  • ~1% water vapor(climate variable)
  • 0.9340% argon
  • 0.0413% carbon dioxide[25]
  • 0.00182% neon[5]
  • 0.00052% helium
  • 0.00019% methane
  • 0.00011% krypton
  • 0.00006% hydrogen

Earth’s atmosphere consists mostly of nitrogen and oxygen. More solar energy is received by tropical regions than polar regions and is redistributed by atmospheric and ocean circulation. Greenhouse gases also play an important role in regulating the surface temperature. A region’s climate is not only determined by latitude, but also by elevation and proximity to moderating oceans, among other factors. Severe weather, such as tropical cyclones, thunderstorms, and heatwaves, occurs in most areas and greatly impacts life.

Earth’s gravity interacts with other objects in space, especially the Moon, which is Earth’s only natural satellite. Earth orbits around the Sun in about 365.25 days. Earth’s axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth’s orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets.

According to radiometric dating estimation and other evidence, Earth formed over 4.5 billion years ago. Within the first billion years of Earth’s history, life appeared in the oceans and began to affect Earth’s atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early 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 life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinctions. More than 99% of all species that ever lived on Earth are extinct. Almost 8 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Humans increasingly impact Earth’s surface, hydrology, atmospheric processes, and other life.

. . . Earth . . .

The modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe.[26] It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was already being used to translate the many senses of Latinterra and Greekγῆ: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð (‘Earth’), a giantess often given as the mother of Thor.[27]

Historically, earth has been written in lowercase. From early Middle English, its definite sense as “the globe” was expressed as the earth. By Early Modern English, many nouns were capitalized, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though earth and forms with the remain common.[26]House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes “Earth” when appearing as a name (for example, “Earth’s atmosphere”) but writes it in lowercase when preceded by the (for example, “the atmosphere of the earth”). It almost always appears in lowercase in colloquial expressions such as “what on earth are you doing?”[28]

Occasionally, the name Terra/ˈtɛrə/ is used in scientific writing and especially in science fiction to distinguish humanity’s inhabited planet from others,[29] while in poetry Tellus/ˈtɛləs/ has been used to denote personification of the Earth.[30]Terra is also the name of the planet in some Romance languages (languages that evolved from Latin) like Italian and Portuguese, while in other Romance languages the word gave rise to names with slightly altered spellings (like the SpanishTierra and the FrenchTerre). The Latinate form Gæa or Gaea (English: /ˈə/) of the Greek poetic name Gaia (Γαῖα; Ancient Greek: [ɡâi̯.a] or [ɡâj.ja]) is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is /ˈɡə/ rather than the more classical English /ˈɡə/.[31]

There are a number of adjectives for the planet Earth. From Earth itself comes earthly. From the Latin Terra comes terran/ˈtɛrən/,[32] terrestrial /təˈrɛstriəl/,[33] and (via French) terrene/təˈrn/,[34] and from the Latin Tellus comes tellurian/tɛˈlʊəriən/[35] and telluric.[36]

. . . Earth . . .

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. . . Earth . . .

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