Earth
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Earth is the third planet from the Sun, and the largest of the four 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. more from Wikipedia
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[edit] Spheres
The Earth, like that of the other terrestrial planets, is chemically divided into layers or spheres. Two sets of spheres have been defined: one set above the surface and one set below. Besides the layers above and below the surface other spheres have been identified such as the hydrosphere, the biosphere and the magnetosphere.
[edit] Above the surface
The Earth's atmosphere is a layer of gases surrounding the planet that is retained by the Earth's gravity. The fuzzy boundary between the atmosphere and outer space is called the exosphere. As we descend toward the surface, we pass through the ionosphere, which includes the exosphere and the thermosphere. Then we go through increasingly dense layers, the mesosphere, the stratosphere and finally the troposphere which contains the gaseous elements and water vapour that sustain life on the planetary surface. The average atmosperic pressure at sea level is 101.325 kPa (1013.25 mbar, or hPa) or 29.921 inches of mercury (inHg) or 760 millimeters (mmHg) of mercury. See International Standard Atmosphere for much more information about how atmospheric pressure is calculated and standardized.
[edit] Below the surfce
Geology of the interior of Earth:
3. upper mantle
4. lower mantle
5. outer core
6. inner core
A: Mohorovičić discontinuity (Moho boundary)
C: Lehmann discontinuity (inner core-outer core boundary)
The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The Inner Core of the earth is believed to be composed primarily of a nickel-iron alloy, with very small amounts of some other elements.[1] The Outer Core of the earth is a liquid layer made of iron and nickel. [Citation needed]
[edit] On and near the surface
[edit] Earth and the Cosmos
[edit] References
- ↑ Lars Stixrude; Evgeny Waserman and Ronald Cohen (November 1997). "Composition and temperature of Earth's inner core". Journal of Geophysical Research 102 (B11): 24729–24740. w:American Geophysical Union. doi:10.1029/97JB02125.
