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Chapter 12 Earth’s Interior Mount Etna, Italy Earth’s Internal Structure Earth’s interior is divided into 3 major layers based on chemical composition Crust, Mantle & Core These layers are further divided based on physical properties Layers of the Earth Gravity and Layering The most dense material (iron) sinks to the center of the planet The least dense material makes up the outer layers Seismic Waves & the Earth’s Interior We learn about the earth’s interior by studying seismic waves Velocities of P & S waves vary as they travel through the earth Travel faster through stiff (rigid) rocks Possible Paths of Seismic Waves The Earth’s Crust Oceanic Forms Crust at mid-ocean ridges Averages 7 kilometers thick Comprised of basalt and gabbro Average density of 3.0 g/cm3 The Earth’s Crust Continental Crust Lots of granite Averages 40 km thick • Thickest ~70 km at mountains • Thinnest ~20 km Basin & Range regions Average density of 2.7 g/cm3 The Mohorovicic Discontinuity The “Moho” is the boundary between the crust & mantle P wave velocities abruptly increase at the “Moho” The Mantle ~80% of earth’s volume Solid rocky layer? Convection Cells Peridotite The “D” layer The Core-Mantle Boundary (Guttenberg Discontinuity) The Outer Core Is a liquid (absence of S waves) Density of 9.9 g/cm3 Mostly iron with some nickel The Inner Core Is a solid Density of 13 g/cm3 Growing as the Earth cools Rotates faster than other layers The Earth’s Temperature Heat flows from hotter to colder areas Earth’s core is 5500° C (10,000° F) Earth’s surface is 0° C (32° F) Heat flows from the core to the surface How Did our Earth Get Hot? Accretion Radioactive Decay Asteroid collision Forming our moon Types of Heat Transfer Conduction Molecular Activity Convection Movement/Circulation Radiation Subatomic Movement Mantle Convection & Plate Tectonics Temperature Profile Geothermal Crust Gradient is 30° C/km Mantle is 0.3°C/km Except the “D” layer Earth’s Magnetic Field Convection of iron in outer core Random reversals throughout history During reversals earth is unprotected End of Chapter 12