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Structure of the Earth

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Structure of the Earth And the ROCK CYCLE Structure of the Earth Compositional (Chemical) Layers Crust: Low density High in silicon (Si) and oxygen (O) Moho: Density boundary between crust and mantle Mantle: Higher density High in Magnesium (Mg) and Iron (Fe) Core: High in Nickel (Ni) and Iron (Fe) Heat Flow in the Earth Heat sources: latent heat from the formation of the Earth Radioactive decay in the core and mantle Temperature in the core: 3000- 5000° C Cooling processes: Convection currents: in outer core and asthenosphere transport heat to the surface Plate tectonics releases heat through the crust (volcanoes) Convection cells in the mantle and core transport heat from the interior of earth to the surface and also return cooler material back into the earth. Mechanical (Physical) Layers of the Earth Lithosphere: Crust and upper, solid part of the mantle; “plates” in plate tectonics Asthenosphere: Partially molten part of mantle; location of convection current that drive plates Outer core: Liquid Inner core: Solid Greatest temperatures, solid due to intense pressure Comparing Compositional Layers to Mechanical Layers Moho What is a Rock? A group of minerals bound together Three major groups: 1) Igneous: Solidified Molten Magma 2) Sedimentary: formed by cementing of sediments. Sediments come from the erosion of other rocks. 3) Metamorphic: Heat and pressure change a rock into something new, without melting. Rock Types Igneous: Solidified molten magma 2 types of Igneous: 1) Extrusive (volcanic) = erupted lava Cools more quickly, so only small crystals form. 2) Intrusive (plutonic) = never erupted magma Cools more slowly within the earth, so larger crystals can form. Silica content (SiO2 = quartz in pure form) determines many things about volcanoes 1) Silica is viscous: a) High silica volcanoes are explosive, due to build-up of pressure within volcano. Viscous lava won’t flow far, so volcanoes are tall and pointy (stratovolcanoes). b) Low silica volcanoes are non- explosive. Lava is runny, so volcanoes are broad and non-pointy (shield shape) Silica content (SiO2 = quartz in pure form) determines many things about igneous rocks 2) Silica is light in color. a) High silica rocks are light in color (pale grey to pink) b) Low silica rocks are dark (due to more dark minerals containing Mg and Fe) Low Silica Medium Silica High Silica Basalt Andesite Rhyolite Extrusive Granite Gabbro Dacite Intrusive Igneous Rock Summary Low in silica High in Silica Rock color = Black Rock color = pale grey, pink Extrusive rock = basalt Extrusive rock = rhyolite Intrusive rock = gabbro Intrusive rock = granite non-viscous (runny) Viscous lava lava Non-explosive Explosive eruptions eruptions Shield volcanoes (low, Stratovolcanoes wide) (tall, pointy) How to identify an igneous rock Large interlocking crystals Floating crystals in a uniform matrix (porphyritic) Glass or no visible crystals Gas bubbles Obsidian Basalt Scoria Geode Sedimentary Rock Sedimentum = “Settling” in Latin, in reference to solid material settling out of a fluid. Two major types: 1) Detrital: formed by compaction and cementation of sediments. 2) Chemical: formed from precipitation of dissolved substances from fluids. Sedimentary Rock Sedimentary rock: formed by compaction and cementation of sediments. Classified Shale by particle size. Sandstone Sedimentary Rock Almost all fossils found in sedimentary rock Almost all fossil fuels (coal, oil, gas) found in sedimentary rock. Arches, Utah Sedimentary Rocks Cont’d Often, sedimentary rocks are layered because they form underwater Layered sediments up close Mt. Everest How to identify a sedimentary rock Layered Contains Fossils Made up of grains Soft and/or crumbly (not interlocking crystals) Metamorphic Rock Metamorphic rock is rock that has been changed by heat and/or pressure (without melting). Two types: 1) Contact or Thermal: caused by proximity to volcanic areas. 2) Regional: caused by deep burial (often during mountain building) , which results in high pressures and temperatures How to identify a Metamorphic Rock Layers are wavy/streaky/folded Rock is often dense and hard Rock is unusually colorful (often green, blue or red with black and white) Rock Cycle: any rock can become any other rock melting weathering melting Rock Cycle in Action .
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