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Geology Review - Geo Study Sheet 1 What are the...

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Geo Study Sheet 1) What are the compositional layers of the earth? What are their compositions? Where (at what depth) are their boundaries? How do we know the answers to these questions? 1. Earths composition. a. Two types of crust. 93% oxygen Continental crust = 35-40 km thick. Felsic to intermediate composition Oceanic crust = approx. 10 km thick. Mafic basalt & gabbro. b. Mantle i. The mantle exists to a depth of 2885 km and can flow in the solid state ii. Separated into lithosphere – contains crust and uppermost mantle. iii. Asthenosphere – part of mantle in which rock can flow c. Core i. The outer core exists to a depth of 5155 km . and is liquid. Due to extreme heat atoms cannot lock into solid framework. Therefore, flows, creates our magnetic field. Liquid iron alloy. ii. The inner core exists from to the center of the earth at 6371 km and is solid. We know these boundaries exists through the study of seismic waves and the velocities at which they travel as well as the paths they take. 2) What are the rheological layers of the earth? What are their rheologies? Where (at what depth) are their boundaries? How do they arise (why does one layer have a different rheology than another?) What are the compositions of the various rheological layers? The crust is brittle. The mantle increases in ductility with depth. 3) What is the Moho? The moho is the crust-mantle boundary.. It occurs between 7-70km below the surface. 4) Why isn’t the mantle completely molten? Because of the enormous amounts of pressure. Also, pressure wins in the heat/pressure battle. 5) What is the geothermal gradient? What is the source/sources of the earth’s heat? The geothermal gradient is the rate at which heat increases with depth. As you move deeper into the earth the geothermal gradient drops. The source of this heat moves through convection, not conduction. Convection is the movement of less dense rock in the lower mantle moving towards the top, as the more dense, cooler rock at the top of the mantle sinks. 6) What does it mean to be a “rock”? What are the three main categories of rocks and what are their key characteristics? Rocks are aggregates of minerals. Igneous: Form from magma. Volcanoes and crystallized lava. Melting, 2. Cooling, 3. Crystallization. Intrusive igneous: coarse grained, slow cooling (forms beneath surface)
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Extrusive igneous: fine grained, fast cooling (volcano or ocean) Names of igneous rock depend on their Si0 2 content o Lower silica = mafic, basalt (high density, low viscosity, ez flowing) / mid range = intermediate / high silica = rhyolite (low density, high viscosity) Silica increases, density decreases. Felsic rock = less dense. Mafic rock = more dense.
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