As a mining engineer, the knowledge of applied geology as it effects design, is required. Also, during the past year I have encountered two geologists that told me they do not believe that plate tectonics is a valid concept of geology. So I would like to say to them, you are wrong. Plate tectonics is a fundamental concept within the scope of geology, and this section will shed a little light on the subject. To begin with, the cross section above, is a cross section of the earth. The earth is comprised of layers of material. The outer layer, the one that we are most familiar with, is the continental crust (also called the Lithosphere). It is 21 miles thick, is relatively a rigid, solid body comprised of felsic material (feldspar and silica composites). The next layer is the oceanic crust, which is about 4.4 miles thick. The oceanic crust is comprised of mafic material (minerals with a high content of magnesium and iron). Further down is the Mantle, which itself has two divisions. First is the asthenosphere (outer mantle), which is in a plastic state, comprised of ultra mafic material (very high in iron and magnesium). Then the lower mantle, which is made up of the same material as the outer mantle, but the lower mantle is solid, not in a state of platsicity. The mantle (both inner and outer) is about 1,790 miles thick. And the final layer is the core. Again, the core has two layers, with the outer core being comprised of base elements, such as iron, cobolt, nickel, reduced silicon. The outer core is in a liquid state, and its revolutions produce the magnetic fields that are present on the earth. The inner core is comprised of the same elements as the outer core, but it is solid. The core (both outer and inner) is about 1,562 miles thick.

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