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The Earth’s Tectonic Plates and Continental Drift

The Earth’s Tectonic Plates and Continental Drift. Continental Drift. In the early 1900’s, German scientist Alfred Wegener proposed a theory that the continents once formed a single landmass he called Pangaea . He suggested they later broke apart and drifted to their current positions.

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The Earth’s Tectonic Plates and Continental Drift

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  1. The Earth’s Tectonic PlatesandContinental Drift

  2. Continental Drift • In the early 1900’s, German scientist Alfred Wegener proposed a theory that the continents once formed a single landmass he called Pangaea. • He suggested they later broke apart and drifted to their current positions. • Wegener’s theory became known as continental drift.

  3. The Breakup of Pangaea

  4. Wegener’s Theory Based on Three Facts • He found fossils of several plants and animals on different continents that could not have crossed the oceans. • He noticed that South America and Africa look like they fit together like puzzle pieces. • He found rock formations in Africa and South America that matched.

  5. Plate Tectonics • The theory that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere. • Origins in Wegener’s work on continental drift.

  6. Three Possible Driving Forcesof Plate Movement • Convection Currents • Ridge Push • Slab Pull

  7. Convection Currents • Hot, rising currents push the tectonic plates apart. • Cooler, sinking currents pull tectonic plates together.

  8. Ridge Push and Slab Pull Ridge Push – At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks into the asthenosphere. Because of ridge push, the oceanic lithosphere slides downhill under the force of gravity. Slab Pull – Because oceanic lithosphere is denser than the asthenosphere, the edge of the tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate with it in a process called slab pull.

  9. Plate Boundary • The area where two different tectonic plates meet.

  10. Three Types of Plate Boundaries • Convergent Boundaries – when two tectonics plates collide. • Continent-Continent • Continent-Oceanic • Oceanic-Oceanic • Divergent Boundaries – when two tectonic plates move away from each other. • A crack, called a rift, forms between them. • New crust is formed as magma rises up through the rift. • Transform Boundaries – when two tectonic plates slide past each other.

  11. Sea-Floor Spreading • The process by which the oceanic crust separates and magma rises from the mantle to form new crust. • Causes underwater mountain chains called mid-ocean ridges. • The magma cools, builds up, and forms an underwater mountain chain.

  12. How Do We Know the Sea-Floor is Spreading? • Magnetic reversals show sea-floor spreading. • Also the best evidence for the theory of continental drift.

  13. Mid Ocean Ridges

  14. Questions????? • What were the three things that made Alfred Wegener come up with the theory of continental drift? • 1. Fossils 2. Continents fit together 3. Rock Formations • What type of plate boundary is a mid-ocean ridge? • Divergent boundary • What are the other two types of plate boundaries? • 1. Convergent boundary 2. Transform Boundary • What was the name of Wegener’s supercontinent? • Pangaea

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