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Chapter 17 Plate Tectonics

Chapter 17 Plate Tectonics. Powerpoint -a-long!. Earth’s Structure (layers of the Earth). The inner core - the solid layer located at the very center of the Earth The outer core - the liquid layer located between the Inner Core and Mantle

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Chapter 17 Plate Tectonics

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  1. Chapter 17 Plate Tectonics Powerpoint-a-long!

  2. Earth’s Structure (layers of the Earth) • The inner core- the solid layer located at the very center of the Earth • The outer core- the liquid layer located between the Inner Core and Mantle • Mantle- The largest layer of the Earth located above the Outer Core • Crust- The outermost layer of the Earth, thickest on land, thinnest on oceans

  3. Crust • Made up of “Tectonic plates”– huge rock slabs that float on the semi fluid mantle • Lithosphere– outer layer of the mantle and crust

  4. Continental Drift Theory • Theory developed Alfred Wegener(1912) • States that: • Earth’s continents were once all joing into a single landmass called “Pangea” • Existed about 200 million years ago (mya) • Name means “all the earth” in Greek • Continents have moved horizontally to their current locations over a long period of time. • Got the idea from “puzzle like” appearance • pieces look like they should fit together.

  5. Evidence of Continental Drift • 1.Fossil Clues • Mesosaurus: prehistoric freshwater reptile found in S. America and Africa • Glossopteris: prehistoric fern found in completely different climates (Africa, Antartica, S. America)

  6. Evidence of Continental Drift • Rock Clues- Appalachian Mountains similar to mountains in Greenland, S. America mountains similar to ones in Africa

  7. Evidence of Continental Drift • Sea-floor Spreading – Molten material in the mantle is forced upward • Material surfaces at mid-ocean ridges (undersea mountain ranges with steep valleys) in the form of magma. This pushes the continents further apart from each other • In some areas, pieces of the crust slip back below the surface and are re-melted.

  8. Evidence of Continental Drift • 4. Age Evidence– no rocks found on sea floor older than 160 mya • Some rocks of continents over 4 Billion years old

  9. Evidence of Continental Drift • 5. Magnetic Clues– Rocks take on current magnetic properties as they form • Iron molecules in the magma “line up” with Earth’s magnetic north and south pole as they cool and crystallize • Magnetic Orientation reverses periodically on Earth, and when it does, any rock being laid down show the opposite magnetic orientation • Rocks being formed now have “reversed” orientation

  10. Evidence of Continental Drift • 6. Climatic Evidence – • Coal deposits form in swamps when dead plants are buried under mud • Antarctica has coal deposits and we’ve found fossils indicating it used to be a temperate swamp • Glacial deposits in India, Africa, and Australia indicate that these areas used to be much colder (probably nearer to the poles!)

  11. The Plate Tectonic Theory • The theory of plate tectonics says that: • Earth’s crust and rigid upper mantle are broken into enormous slabs called “plates” • Tectonic plates move in different directions at different rates over Earth’s surface • The plates interact at places called plate boundaries

  12. The Plate Tectonic Theory • Divergent boundaries: two tectonic plates are moving apart • Mostly found on the ocean floor where they form Mid-ocean ridges • Lots of Volcanoes, hydrothermal vents, and earthquakes in these areas as magma surge up towards the surface • When continental plates separate, it forms a rift valley like that found in Africa

  13. The Tectonic Plate Theory • Convergent boundaries: where two plates are moving towards each other • Can be continental-continental, continental-oceanic, or oceanic-oceanic • Two possible results: • Subduction: one plate slides under the other • Creates a deep-sea trench ( Mariana’s Trench – over 6.8 miles deep) • Recycles and melts down the crust as it enters the mantle • Mountain building: plates push each other upwards to form mountains! • Ex. - Himalayas

  14. The Plate Tectonic Theory • Transform Boundary: plates slide horizontally past each other • Crust is deformed or fractured (cracked) – lots of earthquakes! • Ex. San Andreas Fault

  15. Causes of Plate Motions • Mantle convection: • Convection: transfer of heat energy through the movement of heated matter • Heated air or water rises because it is less dense, colder parts sink because they are more dense • Heat from the Earth’s core causes magma to rise up towards the crust • Cooler parts of the crust sin at convergent boundaries • We don’t know if these are permanent or not, how big they are, or how they form

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