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Drifting Continents

Drifting Continents. Continental Drift Earth was once a super continent called Pangaea (over 200 mya) Proposed by Alfred Wegener. Evidence. 1. Rock Formation Africa & South America 2. Fossils Glossopteris found in cold climates 3. Ancient Climates Coal deposits in Antarctica.

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Drifting Continents

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  1. Drifting Continents Continental Drift • Earth was once a super continent called Pangaea (over 200 mya) • Proposed by Alfred Wegener

  2. Evidence 1. Rock Formation • Africa & South America 2. Fossils • Glossopteris found in cold climates 3. Ancient Climates • Coal deposits in Antarctica

  3. Rejected Hypothesis • Wegener could not explain how continents moved • Rotation of Earth (centrifugal force) disproved • Wegener died in 1930 • 1960’s evidence revealed the process Wegener could not explain

  4. Sea Floor Spreading Technology mapped sea floor • Fathometer (echo sounding device): found mountains, ridges and trenches in sea floor topography • Magnetometer (measures changes in magnetic field): magnetism mirror image on each side of ridge (magnetic symmetry) • Paleomagnetism: study of magnetic records • Magnetic reversal: change in Earth's magnetic field

  5. Harry Hess • Seafloor spreading: crust is formed at ridges and destroyed at deep-sea trenches • Oceanic topography (mountains, valleys, trenches) • Magnetic symmetry (reversal of Earth’s magnetic field) • Isochron: Line on map connects point of same age Missing link to Wagner's theory

  6. Theory of Plate Tectonics • Earth’s crust and ridged upper mantle broken into slabs called plates

  7. Three types of plate boundaries 1. Divergent boundaries • Two plates move away from each other • Form: • oceanic ridges • rift valleys • new crust • Have: • volcanism • earthquakes

  8. 2. Convergent boundaries • Two plates moving toward each other Three types: A. Oceanic-Oceanic convergence • Form: • Trench (subduction) • island arcs • Have: • Volcanism • Earthquakes • Crust is destroyed

  9. B. Oceanic-Continental convergence • Form: • Trench (subduction) • volcanic mountain range • Have: • Volcanism • Earthquakes • Crust is destroyed

  10. C. Continental-Continental convergence • Form: • Folded mountain range • tallest mountains • no subduction • Have: • earthquakes • Crust is deformed

  11. Volcanic Mountains continental oceanic Island Arcs oceanic oceanic Folded Mountains continental continental

  12. 3. Transform Boundaries • Two plates slide horizontally past each other • Crust is only deformed or fractured • Characterized by earthquakes • San Andreas best example

  13. Juan de Fuca Plate Gorda Plate Convergent Divergent

  14. Earths layers: • Lithosphere (crust): Solid, ridge mass; • Oceanic (basaltic, more dense, thinner), • Continental (granitic, less dense thicker) 2. Asthenosphere (mantle): liquid molten area of convection

  15. 3. Core: • Outer: more liquid like than inner core (still very dense due to pressure) made of iron & some nickel, temp 7200 - 9032 ºF (4000-5000ºC). • Inner: solid (due to pressure) made of iron & nickel, temp 9032 - 10832 ºF (5000-6000 ºC). • The outer core and the inner core together cause the earth's magnetism. Because the earth rotates, the outer core spins, the inner core doesn't spin because it's solid. Outer core Inner core

  16. Causes of Plate Motion Mantle Convection • Convection currents in mantle thought to drive plate movement • Creates • Ridge push: weight of uplifted ridge push plate toward trench • Slab pull: weight of subducting plate pulls plate into trench Ridge push Slab pull

  17. Hot spots: areas of volcanic and earthquake activity away from plate boundaries

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