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11/5/2015 Earth’s Internal Structure Earth’s Layers and Zones xkcd.com GEOL 110: GEOLOGY Ch. 12: Earth’s Interior 3 major layers based on chemical composition: • Crust: granitic/basaltic • Mantle: peridotite • Core: iron 4 zones based on physical properties: • Lithosphere (crust and upper mantle): rigid • Asthenosphere: weak, viscous deforming region, convection occurs • Outer core: liquid • Inner core: solid Not for Distribution. For study purposes only for related class. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Earth’s Internal Structure How do we study Earth’s layers? Earth’s Internal Structure How do we study Earth’s layers? • Meteorites: similar to earth composition • Seismic waves • Look at rocks brought up from interior (xenoliths, volcanic eruptions) Stony: olivine & pyroxene, silicates (lithosphere) Iron: nickel & iron (core) © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Earth’s Internal Structure What Caused Layers to Form? Density: Number of molecules per cm3 1 cm What Caused Layers to Form? Gravity and Density • Gravity: force that attracts a body towards the center of the earth Earth’s Internal Structure 1 cm © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 1 11/5/2015 Earth’s Internal Structure What caused layers to form? Earth’s Internal Structure Earth’s Interior Gravity and Density • Gravity: force that attracts a body towards the center of the earth • The densest material (iron) sinks to the center of the planet (eg: bottle filled with air, water, clay, iron) • Gases rise to atmosphere Water: 1.0 Andesite: 2.5 - 2.8 Basalt: 2.8 – 3.0 Peridotite: 3.1 – 3.4 Iron: ~8.0 Nickel: ~9.0 © 2014 Pearson Education, Inc. Probing Earth’s Interior How do we detect the different layers? © 2014 Pearson Education, Inc. Probing Earth’s Interior Seismic waves in Homogenous Material Seismic velocities Seismic Waves • Most knowledge comes from the study of earthquake waves • Seismic rays “fan” out from earthquake source • Generally, travel faster through denser materials. Eg: billiards • Faster through cold (denser) vs. warm • Travel faster through rigid materials • Travel times of P and S waves vary depending on the properties of the materials • Higher velocity in Ocean Crust than Continental Crust http://serc.carleton.edu/eet/seismicwave/going_further.html © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Probing Earth’s Interior Probing Earth’s Interior Seismic Waves in Heterogeneous Material • Reflected wave and refract waves as they pass through the different layers of Earth • Generally, velocities increase with depth • Do not travel in a direct path • Reflect and refract as they pass through the different layers of Earth • Reflect: mirror • Refract: light through prism • Gives a layer-by-layer understanding of Earth’s composition Faster velocity = denser material © 2014 Pearson Education, Inc. Slower velocity= less dense material © 2014 Pearson Education, Inc. 2 11/5/2015 P and S wave Shadow Zones Shadow Zones Seismic Waves: How we detect layers • P-wave shadow zone: P-waves interact with the lowvelocity liquid iron and the outer core, causing rays to be refracted downward, creating a shadow zone. • S-wave shadow zone: S-waves cannot pass through liquids. Inge Lehmann 1888-1993 • Discovered solid inner core and liquid outer core based on seismic waves • 1929 New Zealand earthquake; p waves reflected off a boundary and recorded at other stations. • Lehmann boundary: between inner and outer core • Confirmed in 1970 http://serc.carleton.edu/eet/seismicwave/going_further.html © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Earth’s Layers The Variable and Unusual D Layer Lies at the Base of the Mantle 2 additional Earth Layers •Crust: Ocean and Continental •Moho: boundary between crust and mantle; quick change in velocity •Upper Mantle •Lower Mantle •D”: boundary between mantle and outer core; source of deep mantle plumes and remnants of subducted plates •Outer Core •Inner Core © 2014 Pearson Education, Inc. Press and Seiver, 2002 cseligman.com © 2014 Pearson Education, Inc. End © 2014 Pearson Education, Inc. 3