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Plate Tectonics

Plate Tectonics. Continental Drift. Proposed by German Scientist Alfred Wegener in 1912. Hypothesized that the continents once formed part of a single landmass called a supercontinent. This supercontinent began to break up into smaller continents about 250 million years ago. Continental Drift.

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Plate Tectonics

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  1. Plate Tectonics

  2. Continental Drift • Proposed by German Scientist Alfred Wegener in 1912. • Hypothesized that the continents once formed part of a single landmass called a supercontinent. • This supercontinent began to break up into smaller continents about 250 million years ago.

  3. Continental Drift • Evidence from fossils proved that the continents had once been joined.

  4. Continental Drift • Rock units found in different continents match even though the continents are separated.

  5. Continental Drift • Wegener suggested that if the continents were once joined and positioned differently, evidence of climatic differences would be present.

  6. Mid-Ocean Ridges • Mid-Ocean Ridges are long, undersea mountain chains that have a steep, narrow valley at the center • They form as magma rises, and create new ocean floor as tectonic plates move apart.

  7. Sea-Floor Spreading • New ocean floor is formed as magma rises to Earth’s surface and solidifies at mid-ocean ridges. • Paleomagnetism provides evidence of sea-floor spreading by showing the magnetic symmetry of the ocean floor rocks.

  8. Continental Drift • Explains why and how continents move. • Earth’s crust is classified into two types: • Oceanic crust is dense and made of rock that is rich in Fe and Mg which make it dense. • Continental crust is made of rocks that are rich in silica and is low in density.

  9. Continental Drift • Most scientists agree that there are 15 major tectonic plates. • The edges of these plates are called boundaries. • Boundaries are areas that have frequent earthquakes and volcanoes.

  10. Continental Drift Video ..\..\United Streaming\Continental_Drift.mov

  11. Plate Boundaries • The way that plates move relative to each other determines hw the plate boundary affects Earth’s surface. • There are three types of boundaries: convergent, divergent and transform.

  12. Divergent Boundaries • At divergent boundaries, two plates move away from each other. • Magma from the asthenosphere rises to the surface as the plates move apart. • The magma cools to form new ocean floor. • Creates a mid-ocean ridge with a rift valley. • Example: Atlantic Ocean, Red Sea

  13. Divergent Boundaries

  14. Convergent Boundaries • As plates pull apart at one boundary, the push into neighboring plates at other boundaries. • Convergent boundaries are boundaries that form where two plates collide.

  15. Convergent Boundaries • Because oceanic crust is more dense than continental crust, three types of collisions can happen at convergent boundaries.

  16. Convergent Boundaries • Oceanic-Continental Convergence – the more dense oceanic crust will subduct under the continental crust. This process results in mountain building and volcanic activity. The Pacific Northwest coastline is an example of this type of boundary.

  17. Convergent Boundaries • Oceanic-Oceanic convergence results in the development of a deep ocean trench and island arcs. The islands of Japan is an example of this type of boundary.

  18. Convergent Boundaries • Continental-Continental convergence results in mountain building such as the Himalayan Mountains.

  19. Transform Boundaries • The boundary at which two plates slide past each other horizontally. • Results in earthquakes. • San Andreas Fault

  20. Causes of Plate Motion • The mantle moves in circular currents called convection cells where warm magma rises and cooler magma sinks down toward the core. • This is caused by uneven heating from the core. • The moving magma currents cause the plates to move.

  21. Spreading Zones Video • ..\..\United Streaming\Spreading_Zones.mov

  22. The Changing Continents • Continents break apart by the process of rifting. • Continents grow larger by developing terranes.

  23. Subduction Zones Video • ..\..\United Streaming\Subduction_Zones.mov

  24. Effects of Continental Change • There are changes in climate due to the continents position related to the equator and other continents. • There are changes in living species when geologic changes result in dividing and separating species.

  25. The Supercontinent Cycle • The process by which supercontinents form and break apart over time. • Pangaea formed about 300 mya and started to break up 250 mya. • Slowly the continents moved to their present postition

  26. Current Plate Movements

  27. Geography of the Future • Africa will collide with Europe and the Mediterranean Sea will close up. • East and West Africa will split and a new ocean will form between them. • The Atlantic Ocean will close as North and South America collide with Africa. • The section of Mexico and California that are west of the San Andreas Fault will move towards Alaska. • In 250 million years, a new supercontinent will form.

  28. http://mycontent.discoveryeducation.com/?productCode=US • http://www.learner.org/interactives/dynamicearth/swfs/continents.swf

  29. The End

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