Composition of earth

Layers of the earth based on composition

1) Outer Crust

· Outer layer of the Earth, extending from solid surface down to the first major discontinuity in seismic wave velocity in the lithosphere. Thickness of crust varies from about 8 km under the oceans to about 35 km under the continents.

· There are two kinds of earth crust classified according to two different kinds of rock they contained where each with its own general composition, thickness and density.

(a) Continent Crust: 35 - 60 km thick

relatively low density

granitic rock

average density: 2.8 g/cm3

(b) Oceanic Crust : thickness rarely exceed 5 km

denser material

basaltic composition

average density: 2.9 g/cm3

2) Mantle

• The next major compositional layer of the Earth which covers the core and this zone constitute 82% of its volume and 68% of mass of the Earth. The mantle is composed of iron and magnesium silicate rock, and it goes down to about 2900 km from surface of Earth. The earth's mantle is a heavy layer of rock which lies under the earth's crust. In places where the crust is broken, part of the upper mantle can melt and form a substance called magma, or molten rock. Magma can be forced through the earths crust. It flows out of volcanoes as lava.
• Average density: 4.5 g/cm3

3) Outer core

· It is speculated that the thickness is about 2250 km and it is made of molten iron and nickel. The outer core is so hot that the metals in it are all in the liquid state.

· Average density: 10.7 g/cm3

4) Inner core

· The thickness' is about 1300 km and probably consists of mostly iron and nickel. The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place as a solid. The temperatures may reach 9000 degrees F. and the pressures are 45,000,000 pounds per square inch. This is 3,000,000 times the air pressure on you at sea level!!!

· Average density: 17.0 g/cm3