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Earth Structure

Earth Structure. Mexico quake-- magnitude at 7.0, and epicenter was in the western Pacific state of Michoacan . Its depth was about 40 miles Indonesia-- earthquake off coast of Indonesia Wednesday, April 11 with magnitude of 8.6, sparking tsunami warnings. Lithosphere.

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Earth Structure

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  1. Earth Structure

  2. Mexico quake-- magnitude at 7.0, and epicenter was in the western Pacific state of Michoacan. Its depth was about 40 miles • Indonesia-- earthquake off coast of Indonesia Wednesday, April 11 with magnitude of 8.6, sparking tsunami warnings

  3. Lithosphere • Consists of continental, oceanic and upper part of mantle • Continents composed of granite-type rock, quartz and feldspar minerals, density+2.8g/cm3 • Oceanic crust formed of basalt; basalt rich in iron/magnesium minerals, density+3.0 g/cm3 • Lithosphere is rigid layer of crust and mantle overlying partially-molten asthenosphere

  4. Why Continents Higher and Ocean Floor Lower • Isostacy—Principle that less dense continental crust sits higher on the mantle while denser oceanic crust sits lower • http://www.youtube.com/watch?v=G9rN7qhUQZg&feature=player_detailpage

  5. Continental Drift Evidence • Geographic fit of continents • Fossils • Mountains • Glaciation • Researchers noted geographic fit of continents • e.g. Africa and S. America • Atlantic formed by separation of Africa from S. America • Seuss, 1885, proposed super continent by studying fossils, rocks, mountains • Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea • Evidence supporting the idea that the continents had drifted.

  6. Continental Drift Geographic Fit • Continents seem to fit together like pieces of a puzzle

  7. Continental DriftFossils • Similar distribution of fossils such as the Mesosaurus

  8. Continental DriftMountains • Mountain ranges match across oceans

  9. Continental DriftGlaciation • Glacial ages and climate evidence

  10. Objectionsto theContinental Drift Model • Wegener did not provide a plausible mechanism to explain how the continents could have drifted.

  11. Seafloor Spreading • Continental drift reexamined in 1960’s with new information • New theory developed – Seafloor spreading • Supporting evidence for seafloor spreading • World seismicity • Volcanism • Age of seafloor • Paleomagnetism • Heat flow • Theory combining continental drift and seafloor spreading termed “Plate Tectonics”

  12. Seafloor Spreading • New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches

  13. Evidence for Seafloor SpreadingWorld Seismicity • Earthquake distribution matches plate boundaries

  14. Evidence for Seafloor SpreadingVolcanism • Volcanoes match some plate boundaries; some are hot spots

  15. Evidence for Seafloor SpreadingAge of Seafloor • Youngest sea floor is at mid-ocean ridge • Oldest sea floor away from mid-ocean ridge

  16. Evidence for Seafloor SpreadingPaleomagnetism • When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity) • Earth has a magnetic field - Probably caused by rotation of solid inner core in liquid outer core (both mostly Fe)

  17. Evidence for Seafloor SpreadingPaleomagnetism • Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge.

  18. Seafloor SpreadingHeat Flow • In 1960, convection currents were proposed as driving force to move continents

  19. Theory of Plate Tectonics • John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”

  20. Principles of Plate Tectonics • Earth’s outermost layer composed of thin rigid plates moving horizontally • Plates interact with each other along their edges (plate boundaries) • Plate boundaries have a high degree of tectonic activity • mountain building • earthquakes • volcanoes

  21. Plate BoundariesThree types

  22. Plate BoundariesDivergent • Plates move away from each other • New crust is being formed

  23. Divergent Plate BoundariesExamples Mid-Atlantic Ocean Ridge East African Rift

  24. Plate BoundariesConvergent Three Types: • Ocean-continent • Ocean-ocean • Plates are moving toward each other • Crust is being destroyed • Continent-continent

  25. Convergent Plate BoundariesExamples Mount Fuji, Japan Mount Lassen, California Andes, South America

  26. Plate BoundariesTransform xxxxxxxxxxxxxxxxxxx • Plates slide past one another • Crust is neither created nor destroyed

  27. Transform Plate BoundariesExamples Calexico, California San Andreas Fault Carrizo Plains, Central California

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