First go to https://www.angelfire.com/nj/PflommScience/earthlayers.htm (which is the earth layers lesson) and read that if you haven't already.

As you go deeper into the earth the materials that the earth is made of change.
As you go deeper the density increases.
As you go deeper temperature and pressure increase, but at different rates.
 

The above factors interact, causing the earth to form layers:

Chemical makeup of the layers (what the earth is made of):
    Crust - outermost layer - its rocky silicate material contains much
                aluminum.  Thickness varies from 5 to 40 km.

    Mantle - is about 2,900 km thick.  Its dense rocky silicates contain much
                    iron and magnesium.  It makes up 82 % of the earth's volume and
                    68 % of its mass.

    Core - is about 3,500 km thick.  The metals iron and nickel make up most
                    of the core.  It is very dense.  It makes up 32 % of the earth's mass,
                    but only 16 % of its volume.

Physical Properties of the layers (how the layers behave because of temperature
and pressure differences):
    Lithosphere - outer zone.  It is cool and rigid.  It "floats" on top of the
                    asthenosphere.  The lithosphere includes the crust and the
                    uppermost part of the mantle (from the chemical layers above.)

    Asthenosphere - is soft and flowing, but not completely liquid.
                     This condition is known as plasticity.  It is in the mantle of the
                     chemical layers above. (Temperature - 1,300° C - 1,600° C)
                     Convection (a circular flow of matter from a warmer to a cooler
                     place) is happening in the asthenosphere.

    Mantle - is solid and rigid compared to the asthenosphere.  The temperature
                    is not high enough to overcome the high pressure.
                    Temperature (1,600° C - 3,200° C)

    Outer Core - The temperature is very high and the outer core is liquid.
                    Circulation of molten iron here is thought to be the source of
                    earth's magnetic field.  Temperature (3,200 ° C - 4,000° C)

    Inner Core - Even though the temperature is extremely high, the very high
                    pressure keeps the inner core solid.  Temperature  (4000° C -  4,500° C)

The Lithosphere
The lithosphere includes the crust and the upper mantle is layered.
The two layers are continental crust and oceanic crust.

Continental crust lies under continents.  It varies in thickness.
            Is less dense than oceanic crust.  Has a high percentage of silicon
            and oxygen, and is contains more aluminum. Rocks of this crust
            are granite and rhyolite.
Oceanic crust lies underneath oceans. Is more dense than continental
            crust.  Has denser, darker rocks called basalt and gabbro.
            Some islands are made of oceanic crust (Hawaiian Islands, parts
            of Alaska, Iceland.)

Soils formed from the different rocks of oceanic and continental crust can
be very different. Oceanic crust soil is less fertile.
 

Granite	Rhyolite
Basalt	Gabbro

This is a link to some interesting maps of earth layers.
http://hum.amu.edu.pl/~zbzw/glob/glob34e.htm