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Earth’s Structure

Earth’s Structure. Origin of the Earth. Meteors and Asteroids bombarded the Earth. Gravitational compression. Density Stratified planet. Earth’s Interior. Core. dense. Iron and Nickel. Inner Core - solid. Outer Core - liquid. Mantle. Less dense than core.

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Earth’s Structure

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  1. Earth’s Structure

  2. Origin of the Earth • Meteors and Asteroids bombarded the Earth • Gravitational compression • Density Stratified planet

  3. Earth’s Interior • Core • dense • Iron and Nickel • Inner Core - solid • Outer Core - liquid • Mantle • Less dense than core • Iron and Magnesium silicates • Mostly solid • Upper mantle is partially molten • Crust • Outermost layer • Very thin and rigid • Continental – granite • Density = 2.8 g/cm3 • Oceanic – basalt • Density = 3.0 g/cm3

  4. Granite Basalt Evidence of Internal Structure • Density • calculate density of Earth • Speculate on probable compositions • Meteorites • Use composition and age to determine composition and age of Earth • Seismic waves • Travel times and direction give indication of internal structure of Earth

  5. Types of Seismic Waves • P waves • Primary waves • Push and pull movement • Travel fastest (~ 6 km/sec) • Travel thru solids and liquids • S waves • Secondary waves • Move side-to-side • Slower (~ 4 km/sec) • Travel thru solids only

  6. Seismic Waves Through Earth

  7. 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

  8. Continental Drift Evidence • Researchers noted geographic fit of continents • e.g. Africa and S. America • Atlantic formed by separation of Africa from S. America • Geographic fit of continents • Fossils • Mountains • Glaciation • 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.

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

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

  11. Continental DriftMountains • Mountain ranges match across oceans

  12. Continental DriftGlaciation • Glacial ages and climate evidence

  13. Continental Drift ModelProblems • Alfred Wegener • Presented research to professionals • Did not provide a plausible mechanism to explain how continents drifted

  14. 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”

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

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

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

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

  19. 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)

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

  21. Seafloor SpreadingHeat Flow

  22. Seafloor SpreadingConvection Currents • In 1960, proposed as driving force to move continents

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

  24. 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 high degree of tectonic activity • mountain building • earthquakes • volcanoes

  25. Plate BoundariesThree types • Divergent • Convergent • Transform

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

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

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

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

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

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

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