Mantle
The size of the earth's mantle is about 2,890 km, therefore making it the thickest layer of the earth. Even in the mantle there are 2 parts, the upper mantle and the lower mantle. The upper mantle is about 500 km thick. The lower mantle is about 2300 km thick. The upper mantle contains silicate that is rich in iron and magnesium. The lower mantle is more dense than the upper mantle due to pressure. Movements of the upper mantle is expressed at the crust through the motions of tectonic plates.
http://en.wikipedia.org/wiki/Structure_of_the_Earth and http://www.youtube.com/watch?v=ukqe_6L9V54
http://en.wikipedia.org/wiki/Structure_of_the_Earth and http://www.youtube.com/watch?v=ukqe_6L9V54
http://www.thetech.org/exhibits_events/online/quakes/inside/mantle.html
Check video from 0:30 to 0:50 to find information about the mantle.
http://www.youtube.com/watch?v=ukqe_6L9V54