The Earth is divided into several layers.
(depths in km):
400-650 Transition region
650-2700 Lower mantle
2700-2890 D'' layer
2890-5150 Outer core
5150-6378 Inner core
The crust varies in thickness. It is thinner
under the oceans and it is thicker under the continents. The inner core and crust are solid; the outer core and mantle layers
are plastic or semi-fluid. The layers are seperated by discontinuities (which are evident in seismic data). There is a Mohorovicic
discontinuity between the crust and upper mantle.
The Earth's atmosphere is 77% nitrogen,
21% oxygen, and some traces of argon, carbon dioxide and water. The tiny amount of carbon dioxide in the atmoshere is extremely
important to the Earths surface temperature, the greenhouse effect. The greenhouse effect raises the average surface temperature
about 35 degrees C; without it the ocean would freeze and life would be impossible.
The Earth's chemical composition is: