Earth often referred to as the Earth, Terra, the World or Planet Earth, is the third planet in the solar system in terms of distance from the Sun, and the fifth largest.

It is also the largest of its planetary system's terrestrial planets, making it the largest solid body in the solar system, and it is the only place in the universe known to humans to support life.

The widely accepted scientific theory states that the Earth was formed around 4.57 billion years ago and its natural satellite, the Moon, was orbiting it shortly thereafter, around 4.53 billion years ago.

The outer surface is divided into several tectonic plates that gradually migrate across the surface over geologic time spans.

The interior of the planet remains active, with a thick layer of convecting yet solid Earth mantle and an iron core that generates a magnetic field.

Its atmospheric conditions have been significantly altered by the presence of life forms, which create an ecological balance that modifies the surface conditions.

About 71% of the surface is covered in salt-water oceans, and the remainder consists of continents and islands..

For more information about the topic Earth, read the full article at Wikipedia.org, or see the following related articles:

Shift of equinox — The precession of the equinoxes refers to the precession of Earth's axis of rotation with respect to inertial space. The precession of the equinoxes ...  > read more

Solstice — The summer solstice is an astronomical term regarding the position of the sun in relation to the celestial equator. The summer solstice is the day of ...  > read more

Circle of latitude — On the Earth, a circle of latitude or parallel is an imaginary east-west circle that connects all locations with a given latitude. The position on ...  > read more

Tide — Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the Earth. Tides cause ...  > read more

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Are Earth's Oceans Made Of Extraterrestrial Material? (November 11, 2009) — Contrary to preconceived notions, the atmosphere and the oceans were perhaps not formed from vapors emitted during intense volcanism at the dawning of our planet. Scientists now suggest that water ...  > read more

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Discovering A New Earth 430 Light Years Away

Earth  is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass.

It is also referred to as the Earth, Planet Earth, Gaia, Terra, and "the World." Home to millions of species including humans, Earth is the only place in the universe known to harbor life.

Scientific evidence indicates that 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. 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 23.4° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year.

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.

Long term periodic changes in the Earth's orbit, caused by the gravitational influence of other planets, are believed to have given rise to the ice ages that have intermittently covered significant portions of Earth's surface in glacial sheets. Tectonic Theory 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 mantle.

The asthenosphere behaves like a superheated and extremely viscous liquid. 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 Surface 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..

For more information about the topic Earth, read the full article at Wikipedia.org, or see the following related articles:

Shift of equinox — The precession of the equinoxes refers to the precession of Earth's axis of rotation with respect to inertial space. The precession of the equinoxes ...  > read more

Circle of latitude — On the Earth, a circle of latitude or parallel is an imaginary east-west circle that connects all locations with a given latitude. The position on ...  > read more

Solstice — The summer solstice is an astronomical term regarding the position of the sun in relation to the celestial equator. The summer solstice is the day of ...  > read more

Solar radiation — Solar radiation is radiant energy emitted by the sun, particularly electromagnetic energy. About half of the radiation is in the visible short-wave ...  > read more

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Hot Climate Could Shut Down Plate Tectonics (May 13, 2008) — A new study of possible links between climate and geophysics finds that a much hotter climate could shut down the Earth's plate tectonics. While human-induced climate change couldn't generate the ...  > read more

Earth Structure: Fluid Factory In Solid Earth (March 3, 2009) — Earth is a giant fluid factory, according to new research. Earth scientists propose a new model for the nature and distribution of fluids from the core to Earth’s based on modern concepts of ...  > read more

Are Earth's Oceans Made Of Extraterrestrial Material? (November 11, 2009) — Contrary to preconceived notions, the atmosphere and the oceans were perhaps not formed from vapors emitted during intense volcanism at the dawning of our planet. Scientists now suggest that water ...  > read more

When The Earth Dried Out (February 11, 2002) — About a billion years ago, the continents emerged relatively suddenly from an ocean that covered 95 percent of the Earth's surface, according to a new theory by Eldridge Moores, a geologist at ...  > read more

Texas A&M Oceanographer Challenges Plate Tectonics As Reason For Poles' Shift (January 25, 2000) — Millions of years before Carole King felt the earth move under her feet, the planet rapidly and drastically shifted on its axis, according to research by Texas A&M University oceanographer ...  > read more

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Discovering A New Earth 430 Light Years Away