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Earth’s Structure

Earth’s Structure. Origin of the Earth. Meteors and Asteroids bombarded the Earth. Earth is 4.6 billion years old. 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.

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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 Earth is 4.6 billion years old

  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. Earth’s Structure

  6. Earth’s Layers

  7. 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

  8. Seismic Waves Through Earth

  9. Continents Today

  10. Continental Drift Theory • In 1912 a German meteorologist and explorer named Alfred Wegener presented a theory that the continents were once joined together in one land mass and have over millions of years slowly drifted apart into their present positions as we see them today. He named the supercontinent “Pangaea” after the Greek word meaning “all land”.

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

  12. Continental Drift Theory • Through Wegener’s research he found evidence to support his theory: • Fossils of Glossopteris, a seed fern, was found in India, Australia, South America, Africa and Antarctica • Fossils of Mesosaurus, a small reptile were found in freshwater deposits in Africa & South America.

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

  14. Glossopteris • Fern

  15. Continental Drift • Layers of the mountains found in S.E. Brazil, South America and S.W. Africa line up layer for layer in exact format. • Continents look like puzzle pieces that could fit together.

  16. Continental DriftMountains • Mountain ranges match across oceans

  17. Continental DriftGlaciation • Glacial ages and climate evidence

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

  19. 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”

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

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

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

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

  24. 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)

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

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

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

  28. 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

  29. Plate BoundariesThree types • Divergent • Convergent • Transform

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

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

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

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

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

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

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