Earth's Dynamic Forces: A Journey Through Plate Tectonics

1. Chapter 1 Section 2 Changes Within the Earth

2. Plate Tectonics • The earth’s outer shell is not one solid sheet of rock • The lithosphere and mantle are broken into a number of moving plates • These plates are not anchored in place, but slide over a hot and flexible layer of the mantle

3. Continental Drift Theory • Alfred Wegener proposed that there was once a single continent “Pangaea” • 180 million years ago, Pangaea began to break into separate continents • He used fossils from around the world to prove his theory • Many scientists stillremain unconvinced of this theory

4. Pangaea

5. Seafloor spreading • The ocean floor is not flat • Scientists found many different landforms on the ocean’s floor • The rocks from the ocean floor were much younger than the rocks on the continents • Theory: Molten rock from the mantle rises beneath the underwater ridge and breaks through a split (rift valley) • The rock then spreads in both directions

6. Opposition • “How dothe continents move?” • “What force is powerful enough to send gigantic plates sliding around the earth?” • Today, scientists believe it is convection

7. Spreading • When plates pull away from each other, they form a verging plate boundary, or spreading zone. • Examples: rift valley, earthquakes, volcanic action

8. Subduction • When an oceanic plate meets a continental plate, it slides beneath the lighter plate down toward the mantle • Oceanic plates are denser than continental plates • Examples: volcanoes which will form mountains

9. Convergence • When two continental plates collide, neither will sink • Buckling, folding, and faulting of rocks pressed against each other will produce mountain ranges • Example: Himalayas

10. Faulting • When two plates slip or grind past each other • Example: San Andreas Fault, CA