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Earth is the third planet from the Sun, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density. It is also referred to as the World, the Blue Planet, and Terra.

Home to millions of species, including humans, Earth is the only place in the universe where life is known to exist. 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. The physical properties of the Earth, as well as its geological history and orbit, allowed life to persist during this period. The world is expected to continue supporting life for another 1.5 billion years, after which the rising luminosity of the Sun will eliminate the biosphere.

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 (365.24 solar days). 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. Between approximately 4.1 and 3.8 billion years ago, asteroid impacts during the Late Heavy Bombardment caused significant changes to the surface environment.

Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. The inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in Earth being the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.

For more information about Earth, read the full article at Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.

News tagged with earth

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As the World Churns

Space & Earth / Earth Sciences

Dec 28, 2009 | 4.4 / 5 (14) | 25

(PhysOrg.com) -- "Terra firma." It's Latin for "solid Earth." Most of the time, at least from our perspective here on the ground, Earth seems to be just that: solid. Yet the Earth beneath our feet is actually ...

Titan's lakes could be explored by boat

Space & Earth / Space Exploration

Dec 22, 2009 | 4.6 / 5 (10) | 1

(PhysOrg.com) -- If a suggestion to be made to NASA comes to fruition, vast lakes thought to be filled with liquid hydrocarbons near the north pole of Saturn's moon Titan, may one day be explored by boat.

Forests take center stage at Copenhagen

Space & Earth / Environment

Dec 17, 2009 | 3 / 5 (2) | 0

As the UN Climate Conference in Copenhagen approaches its conclusion, negotiations are focusing on the role of forests in mitigating climate change. The new 'Reducing Emissions from Deforestation and Forest ...

From greenhouse to icehouse -- reconstructing the environment of the Voring Plateau

Space & Earth / Earth Sciences

Dec 15, 2009 | 4.3 / 5 (8) | 1

The analysis of microfossils found in ocean sediment cores is illuminating the environmental conditions that prevailed at high latitudes during a critical period of Earth history.

Valuable, rare, raw earth materials extracted from industrial waste stream

Space & Earth / Environment

Dec 15, 2009 | 4.6 / 5 (9) | 5

Fierce competition over raw materials for new green technologies could become a thing of the past, thanks to a discovery by scientists from the University of Leeds.

Scientist uncovers relics of ancient cosmos

Space & Earth / Space Exploration

Dec 14, 2009 | 4.5 / 5 (19) | 3

(PhysOrg.com) -- A University of Manchester scientist, working as part of an international team, has uncovered an unexpectedly rich trove of relicts from the ancient cosmos.

California's troubled waters: Satellite-based findings reveal major groundwater loss in Central Valley (w/ Video)

Space & Earth / Earth Sciences

Dec 14, 2009 | 5 / 5 (1) | 0

New space observations reveal that since October 2003, the aquifers for California's primary agricultural region - the Central Valley - and its major mountain water source - the Sierra Nevada - have lost nearly ...

Earth's atmosphere came from outer space, find scientists

Space & Earth / Earth Sciences

Dec 10, 2009 | 4.2 / 5 (29) | 12

(PhysOrg.com) -- The gases which formed the Earth's atmosphere - and probably its oceans - did not come from inside the Earth but from outer space, according to a study by University of Manchester and University ...

Life on Mars theory boosted by new methane study

Space & Earth / Space Exploration

Dec 08, 2009 | 4.9 / 5 (31) | 11

Scientists have ruled out the possibility that methane is delivered to Mars by meteorites, raising fresh hopes that the gas might be generated by life on the red planet, in research published tomorrow in Earth an ...

Study: Earth more sensitive to carbon dioxide than previously thought

Space & Earth / Earth Sciences

Dec 06, 2009 | 3 / 5 (52) | 91

In the long term, the Earth's temperature may be 30-50% more sensitive to atmospheric carbon dioxide than has previously been estimated, reports a new study published in Nature Geoscience this week.

Partial lunar eclipse will take place on 31st December

Space & Earth / Space Exploration

Dec 03, 2009 | not rated yet | 0

(PhysOrg.com) -- In a lunar eclipse, the Earth, Sun and Moon are almost exactly in line and the Moon is on the opposite side of the Earth from the Sun.

Forest deal at Copenhagen must avoid creating 'carbon refugees'

Space & Earth / Environment

Dec 03, 2009 | not rated yet | 1

Forest dwellers must be included in the design of the upcoming forest deal at Copenhagen in order to avoid a humanitarian crisis, according to a scientist at the University of Leeds.

Professor foresees rising Antarctic snowmelt

Space & Earth / Earth Sciences

Dec 03, 2009 | 3.5 / 5 (2) | 0

The 30-year record low in Antarctic snowmelt that occurred during the 2008-09 austral summer was likely due to concurrent strong positive phases for two main climate drivers, ENSO (El Niño - Southern Oscillation) and SAM ...