Earth

Earth (from Old English: Eorðe; Greek: Γαῖα Gaia; Latin: Terra), otherwise known as the World (especially in geopolitics and geography), or the Globe, 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.

3D-Clouds.jpg

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.

67º Período de Sesiones de la Asamblea General de Naciones Unidas (8020913157).jpg Headquarters of the United Nations in New York City

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.

AYool topography 15min.png Present-day Earth altimetry and bathymetry. Data from the National Geophysical Data Center.

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 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures; politically, the world has about 200 sovereign states.

AxialTiltObliquity.png Earth's axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit
Continents vide couleurs.png The seven continents of Earth
Earth-Moon.svg Details of the Earth–Moon system, showing the radius of each object and the Earth–Moon barycenter. The Moon's axis is located by Cassini's third law.
Earth-cutaway-schematic-english.svg
Earth2014shape SouthAmerica small.jpg Shape of planet Earth. Shown are distances between surface relief and the geocentre. The South American Andes summits are visible as elevated areas. Data from the Earth2014 global relief model.
Earth elevation histogram 2.svg Elevation histogram of Earth's surface
Earth symbol.svg
EpicEarth-Globespin(2016May29).gif Earth's rotation imaged by DSCOVR EPIC on 29 May 2016, a few weeks before the solstice
Felix from ISS 03 sept 2007 1138Z.jpg Hurricane Felix seen from low Earth orbit, September 2007 Lenticular cloud with a pressure ridge near Mount Discovery, Antarctica, November 2013 Massive clouds above the Mojave Desert, February 2016
FullMoon2010.jpg Full moon as seen from Earth's Northern Hemisphere
Full moon partially obscured by atmosphere.jpg This view from orbit shows the full Moon partially obscured by Earth's atmosphere.
Geoids sm.jpg Earth's gravity measured by NASA's GRACE mission, showing deviations from the theoretical gravity. Red shows where gravity is stronger than the smooth, standard value, and blue shows where it is weaker.
MODIS Map.jpg Satellite image of Earth cloud cover using NASA's Moderate-Resolution Imaging Spectroradiometer
Moraine Lake 17092005.jpg The Rocky Mountains in Canada overlook Moraine Lake.
NASA-Apollo8-Dec24-Earthrise.jpg Earthrise, taken by astronauts on board Apollo 8
Pale Blue Dot.png The Pale Blue Dot photo taken in 1990 by the Voyager 1 spacecraft showing Earth (center right) from nearly 6.4 billion km (4 billion mi) away
Pavlof2014iss.jpg A volcano injecting hot ash into the atmosphere
PhylogeneticTree, Woese 1990.PNG Speculative phylogenetic tree of life on Earth based on rRNA analysis
Pressure ridges Scott Base lrg.jpg
Protoplanetary-disk.jpg Artist's impression of the early Solar System's planetary disk
Structure of the magnetosphere-en.svg Schematic of Earth's magnetosphere. The solar wind flows from left to right
Tectonic plates (empty).svg
The Earth seen from Apollo 17.jpg
Thunderstorm Arch (5740783227).jpg A natural stone arch, showing rock layers

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