Geog 101 Geog 101
Minnesota State University, Mankato
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This 3 page Class Notes was uploaded by Hallie Notetaker on Friday September 16, 2016. The Class Notes belongs to Geog 101 at Minnesota State University - Mankato taught by Phillip Larson in Fall 2016. Since its upload, it has received 38 views. For similar materials see Introductory Physical Geography in Geography at Minnesota State University - Mankato.
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Date Created: 09/16/16
Making Earth’s Basic Configuration The Interior of the Earth Layers in order from inside out o Inner core (solid) 6370 km – 5150 km o Outer core (liquid) 5150 km – 2900 km o Mantle (solid, but plastic) Lower 2900 km – 670 km, Upper 670 km – 250 km o Crust (solid, rigid) ~70km – 0 km The upper most mantle and crust Lithosphere 250 km – 0 km Directly below that Asthenosphere 250 km – 70 km Rest of mantle Mesosphere Composed of either oceanic or continental crust Density is different Oceanic = 3.0 g/cm^3 Continental = 2.7 g/cm^3 Inner Core Transition between inner and outer core may be several hundreds of km’s wide Radius of 1220 km o 70% of the Moon’s radius Approximately 5430 degrees Celsius o Roughly equivalent to the temperature at the surface of the sun Likely made of solid iron and nickel o Iron can be solid because the intense pressure results in higher melting temperatures Solidus o Extremely dense 12.8-13.1 g/cm^3 Outer Core Boundary between outer core and mantle varies several hundred km Gutenberg Discontinuity – contact between outer core and mantle Approximately 4030 degrees Celsius Likely made of liquid iron and nickel o Low viscosity fluid – less pressure, still high temperature o Convects turbulently o Convective currents are believed to generate Earth’s magnetic field o As convection continues over time, it is thought that the basal boundary of the outer core freezes, thus the inner core grows at about one mm per year o Density of 10.7 g/cm^3 Lower Mantle The lower and upper mantle make up 60% of Earth’s total volume o Contains about 50% of mass Broad transition zone between 410 km and 660 km separates the upper and lower mantles Temperatures range from 500 to 4000 degrees Celsius, with depth, throughout the entire mantle Mantle is mostly solid, but can behave viscous-like (plastic) Mantle is made of oxygen, magnesium, silica, iron, calcium, aluminum (in descending order of abundance) o Minerals include quartz, magnesium oxide, ferrus oxide, aluminum oxide, silicates, olivine, pyroxenes, garnet, high density minerals like perovskite, etc. o Rocks – peridotite, dunite, eclogite o Denser materials at greater depths Upper Mantle Contains ~10% of mass Includes lowest portion of the Lithosphere and all of the asthenosphere o Reaches further to the contact with the Lower Mantle o Between the asthenosphere and lower mantle is much more solid Partially solid, partially molten o Less pressure allows for more melting Boundary with crust is variable in depth o Continental crust is thick o Oceanic crust is thin Moho, or Mohorovicic Discontinuity – contact between crust and mantle Asthenosphere and Lithosphere Asthenosphere – behaves like a plastic, meaning highly viscous and ductile deformation o 250 km – 70 km in depth o Lithosphere/Asthenosphere boundary is typically at the 1300 degrees Celsius isotherm Boundary between brittle and ductile behavior in these rocks o Slowly deforms and moves; capable of flow Under oceanic plates Asthenosphere is much closer to the surface Lithosphere – upper most mantle and crust o Behaves rigidly, brittle o Fractures, faults, breaks o What we live on Solidus Mantle is not molten o Although temperature increases with depth, so does the pressure and thus the melting point increases Crust Crustal thickness varies depending on the types of crust present o Oceanic crust – 6-10 km thick o Continental crust – 10-70 km thick Continental crust o SiA, along with K, Ca, Na o Average composition – andesite, granite Oceanic crust o SiMa, along with Fe o Average composition – basalt How do we know the interior structure? Study seismic waves o When an earthquake occurs we can record the details of how the waves travel through the Earth’s interior Based on how they move, we can theorize about what they are traveling through Seismic wave velocity depends on the composition, mineral phase, structure, temperature and pressure of the material through which the waves pass o Seismic waves travel quicker through denser materials o Hotter areas slow down seismic waves o Liquid areas slow down seismic waves o Thus, molten areas slow down P-waves and stop S-waves Partially molten areas may slow down P-waves and partially attenuate S- waves P-waves – compressional, primary waves S-waves – transverse, secondary waves Moho – Mohorovicic Seismic Discontinuity (1909) – travel times change from 6 km/sec to 8 km/sec o This marks the crust-mantle boundary Low velocity zone – at depths between 100 km and 250 km P-waves slow and S-waves are weakened or attenuated o This is thought to be the asthenosphere (or weak sphere) where it is partially molten (>1%) 670 Discontinuity – below the low velocity zone seismic velocities increase o This indicates wave propagation through more dense materials of the lower mantle Gutenberg – P-waves are severely refracted (bent) and S-waves stop completely at 2900 km o This signifies the molten outer core Lehman – sudden increase in P-wave velocity at depth of 5150 km o Denser inner core
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