GEOL 106 - LEC 8

What causes the stress in the earth? • That’s what we need to answer now. So lets look at the dynamic earth system more closely Structure of the earth • Seismic waves have been critical in giving us a “picture”of the inside of the earth ( an “xray” of the Earth ). The waves are reflected and refracted at boundaries between different materials. • Waves reveal a layered earth • P and S wave .. P waves can go through liquid .. s waves cant.. determines 3 layers. Mantle, Outer core and Inner core. We live on crust. 2900 km from crust to get to outer core ( depth of mantle) .. 5100 km from crust to get to core… 6371 km to get to centre of earth. Mantle (solid) outer core (liquid) inner (solid) . • Continental crust in about 30 km thick and oceanic crust in 5 km thick. • Moho is the boundary between the crust and mantle. • Moho stands for Mohorivicic Discontinuity .. What about the composition of the layers. • The core of the earth . outer/inner is mostly out of iron (Fe). And the mantle is made out of minerals called silicates (O, Si, Mg, Fe,Al,etc ) .. Iron, oxygen, silicon , aluminum , magnesium (Silicates :minerals that have O and Si as their basic building blocks) • Chemical Composition of Mantle .. order of decreasing abundance (by weight) … O. Si