Earth
From Space Wiki
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Earth (often referred to as "the earth") is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. It is the largest of its planetary system's terrestrial planets and the only place in the universe known by humans to support life. The Earth was formed around 4.57 billion years ago[1] (see Age of the Earth) and its largest natural satellite, the Moon, was orbiting it shortly thereafter, around 4.533 billion years ago.
Since it formed, the earth has changed through geological and biological processes that have hidden traces of the original conditions. 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. The atmospheric conditions have been significantly altered by the presence of life forms, which create an ecological balance that modifies the surface conditions. About 70% of the surface is covered in salt water oceans, and the remainder consists of continents and islands.
There is significant interaction between the earth and its space environment. The relatively large moon provides ocean tides and has gradually modified the length of the planet's rotation period. A cometary bombardment during the early history of the planet is believed to have formed the oceans. Later, asteroid impacts are understood to have caused significant changes to the surface environment. Changes in the orbit of the planet may also be responsible for the ice ages that have covered significant portions of the surface in glacial sheets.
The Earth's only natural orbiting body is the Sun, although the asteroid Cruithne has been erroneously described as such. Cruithne was discovered in 1986 and follows an elliptical orbit around the Sun at about the same average orbital radius as the Earth. However, from the point of view of the moving Earth, Cruithne follows a horseshoe orbit around the Sun that avoids close proximity with the Earth.
It is the second known planet known to have intelligent life. The other being the planet Krypton, home to the alien Superman.
[edit] References
- NASA's Earth fact sheet
- Discovering the Essential Universe (Second Edition) by Neil F. Comins (2001)
- space.about.com - Earth - Pictures and Astronomy Facts
[edit] Notes
- ↑ G.B. Dalrymple, 1991, "The Age of the Earth", Stanford University Press, California, ISBN 0-8047-1569-6.
[edit] External links
- WikiSatellite view of Earth at WikiMapia
- USGS Geomagnetism Program
- Overview of the Seismic Structure of Earth PDF
- NASA Earth Observatory
- Beautiful Views of Planet Earth Pictures of Earth from space
- Java 3D Earth's Globe
- Projectshum.org's Earth fact file (for younger folk
- MySolarSystem.com - Earth Facts about Earth and the moon.
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| The Sun · Mercury · Venus · Earth · Mars · Ceres* · Jupiter · Saturn · Uranus · Neptune · Pluto* · Eris* · Sedna* | |||
| Planets · Dwarf planets · Moons: Terran · Martian · Asteroidal · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian | |||
| Pluto' * Ceres * Eris * Haumea * Makemake | |||
| Small bodies: Meteoroids · Asteroids (Asteroid belt) · Centaurs · TNOs (Kuiper belt/Scattered disc) · Comets (Oort cloud) | |||
| planets with '*' are dwarf's but listed between 'real planets'. | |||
| See also astronomical objects and the solar system's list of objects, sorted by radius or mass. |
