Layers of the Earth

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  • Topic: Lithosphere, Earth, Mantle
  • Pages : 3 (962 words )
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  • Published : February 17, 2013
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1.Crust: The Earth's surface is composed mostly of water, basalt and granite. Oceans cover about 70% of Earth's surface. The Earth's thin, rocky crust is composed of silicon, aluminum, calcium, sodium and potassium. The crust is divided into continental plates which drift slowly (only a few centimeters each year) atop the less rigid mantle. The crust is thinner under the oceans; this is where new crust is formed. Continental crust is about 25-90 km thick.

2.Mantle: Under the crust is the rocky mantle, which is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. The upper mantle is rigid and is part of the lithosphere (together with the crust). The lower mantle runs slowly, at a rate of a few centimeters per year.

3.Core: The Earth has an iron-nickel core that is about 2,100 miles in radius. At the core-mantle boundary, composition changes. Seismic waves suggest this material is of a very high density (10-13 g/cm3), which can only correspond to a configuration of metals rather than rock. The presence of a magnetic field around the earth also indicates a molten metallic core. Unlike the crust and the mantle, we don’t have any samples of the core to look at, and therefore there is some disagreement about its exact composition.

4.Inner Core: The inner core may have a temperature up to about 13,000°F (7,500 K), which is hotter than the surface of the Sun. It has a radius of about 750 miles and is solid. The inner core is considered to be solid because of the behavior of P and S waves passing through it.

5.Outer Core: The outer core is in a liquid state and is about 1,400 miles (2,260 km) thick. The outer core is presumed to be liquid because it does not transmit shear (S) waves and because the velocity of compressional (P) waves that pass through it is sharply reduced.

6.Lithosphere: The lithosphere can be defined as part of the solid outermost surface of a planet. It is the approximate 100 first sturdy and stony kilometers of...
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