3. Continental Drift Theory Flaws 1 st What force could push large mass over great distances 2 nd How the continents could move were through something solid like earth’s crust They questions were the reasons why Wegener’s theory was rejected until the 1950s

4. WWII Sub Warfare Sonar tech was improved in order to create detailed maps and way to navigate Magnetometers: device that detect small changes in magnetic fields, towed behind boats to locate enemy subs Data from these sources revealed vast underwater mountain chains called ocean ridges and deep sea trenches

5. Ocean Rocks & Sediment Rock Analysis The age of the rocks varies and the variations were predictable Samples near the ocean ridges were younger than the samples taken near the trenches..

6. Seafloor Spreading Theory Explains how ocean crust is formed at ocean ridges and destroyed at deep- sea trenches Supports Wagener’s continental drift theory Unlike Wagner’s theory: continents are not push through ocean crust, in fact riding along while ocean crust moves from ocean ridges Think of a Conveyor Belt

7. Seafloor Spreading Theory The evidence for Seafloor Spreading suggest continental and ocean crust move as enormous slabs labeled Tectonic Plates

8. Tectonic Plates Tectonic Plates: huge piece of crust & upper mantle that fit together at their edges to cover Earth's surface There are about 12 major plates and several smaller ones Move a few centimeters a year similar to the rate at which fingernails grow

9. Theory of Plate Tectonics Theory that describes how tectonic plates move and shape Earth's surface Move in different directions @ different rates Edges of the plates are called boundaries

11. Plate Boundaries Plate Interaction - The plates interact with each other along three types of plate boundaries: Divergent Boundaries Convergent Plate Boundaries Transform Boundaries Because of the motion of the plates they can collide, pull apart, or scrap against each other

13. ANY QUESTIONS?