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What the Earth is made of?

The Earth is divided into several layers.
      (depths in km):
                           0-40  Crust
                         40-400 Upper mantle
                         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:
               (by mass)
                                34.6% Iron
                                29.5% Oxygen
                                15.2% Silicon
                                12.7% Magnesium
                                 2.4% Nickel
                                 1.9% Sulfur
                                0.05% Titanium