GEO 155 1st Edition Lecture 24 Last Lecture Erosion on Slopes Outline of Current Lecture I Earth s Internal Structure II Continental vs Oceanic Crust III Plate Tectonics a Major Plate i Boundaries b Interaction of Plate Boundaries i Divergence ii Convergence iii Transform Current Lecture Earth s Internal Structure Less know than atmosphere Most pressure concentrated in inner core of earth solid Liquid outer core Mantle Less dense than outer core These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 1 Lower mantle solid thick little movement 2 Upper mantle highly viscous strong interaction with crust a Low part below asthenosphere is mostly solid and plastic like b Upper part is rigid like crust asthenosphere c Lithosphere is above asthenosphere below the crust Asthenosphere Rock is plastic like and flows readily with pressure Tectonic plates float on top Crust Less dense than upper mantle Separated from mantle by Mohorovicic Moho discontinuity o Thickness not consistent Moho closer under ocean floor Moho deeper for continental land masses Continental and Oceanic Crusts Bottom ocean rocks are darker and denser Mafic rock Continental rocks have lowest density Felsic rock Continental Drift Francis Bacon noticed coasts of South America and Africa fit together like a puzzle Alfred Wegener noted that all landmasses were united in a giant supercontinent during Paleozoic and Mesozoic eras Pangaea Continental drift is the slow movement of continents away from Pangaea Evidence of Pangaea Fossil records are similar on different continents suggesting they were all once connected Mid Oceanic Ridges Mostly submarine mountain ranges o Example Mid Atlantic Ridge Sea floor spreading along ridges creation of a new lithospheric material and its continuous movement away from it source o Deep ocean basalt rocks much younger than continental o Proves continental drift by movement of plate tectonic Theory of Plate Tectonics Explain continental drift by movement of large lithospheric plates floating on asthenosphere Explains formation movement and destruction of plates Movement of Plates Plates move at velocities o 1 12 cm per year Movement of plates directly responsible for many of Earth s major topographic or bathymetric features Landforms created depend on interaction of two plates by 1 Divergence two plates move away from each other by tensional forces crust thinned and broken by faults a Oceanic example ridges b Continental rift valleys form starts in continents but create oceans i Example East Africa Rift Valley and Red Sea formed when Arabian and African plates separated 2 Convergence two plates move toward each other a Depends on type of lithosphere i If oceanic crust involved subduction occurs and one of the crustal plates pushed below the other denser 1 Subduction Zone water carried by ocean plate forced down into overlying plate triggering melting of rock a Some molten rock forced up through vents and fissures to surface VOLCANISM b Intense tectonic activity EARTHQUAKES 2 Oceanic continental subduction continental rocks crumpled into mountain range often with volcanoes e g Andes 3 Oceanic oceanic subduction deep ocean trenches and volcanic island arcs e g Philippines 4 Continental continental no subduction produces massive mountain range 3 Transform two plates slide past each other a Earthquakes and crustal deformation regularly occur i E g San Andreas Fault Pacific and North American Plate interact
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