1. Plate Tectonics

2. Continental Drift
Wegener’s Hypothesis The continents once formed part of a single landmass called a supercontinent. The supercontinent began breaking up into smaller continents about 250 million years ago. Over millions of years, these continents drifted to their present locations.

3. Wegener’s Evidence
Fossil Evidence: identical fossils found in both South America and western Africa Coastline Evidence: similarities in the coastlines of the continents Geologic Evidence: ages and types of rocks in the coastal regions of separate continents matched. Coal found in cold regions. Climatic Evidence: layers of debris from ancient glaciers on separate continents

5. Mid-Ocean Ridge
Undersea mountain chain that forms as magma rises and creates new sea floor as tectonic plates move apart

6. Sea-Floor Spreading
New sea floor forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge

7. Magnetic reversals
 Geologic evidence suggest that Earth’s magnetic field has not always pointed north.

8. Magnetic Symmetry
The stripes in the sea floor illustrate Earth’s alternating magnetic field

9. Plate Boundaries

10. Divergent Boundaries Plates move away from each other.
Magma from the asthenosphere rises to the surface, cools and forms new oceanic lithosphere.

11. Convergent Boundaries Plates collide with each other
Convergent Boundaries Plates collide with each other. Three types of collisions can happen at convergent boundaries.
First Type: Dense oceanic lithosphere collides and sinks or subducts under the less dense continental lithosphere.

12. Convergent Boundaries
Second Type: Two continental lithosphere plates collide. Neither subducts instead the colliding edges crumple and thicken, which causes uplift that forms large mountains ranges.

13. Convergent Boundaries
Third Type: Two oceanic lithosphere plates collide. One plate subducts under the other plate, and a deep-ocean trench forms. Magma rises to the surface to form an island arc, which is a chain of volcanic islands.

14. Transform Boundaries
Two plates slide past each other horizontally. They scrape against each other in a series of sudden spurts of motion that are felt as earthquakes.
Short segments of mid-ocean ridge are connected by transform boundaries called fracture zones.

15. Causes of Plate motion
Mantle Convection: Earth’s core and radioactivity within the mantle heat mantle material. The hot material rises, the cooler material sinks. As the mantle moves it drags the plates along with it.

16. Plate Motion
Ridge Push: Warm and less dense than older rock the newly formed rock rises and pushes the older denser rock away from the ridge.

17. Plate Motion
Slab Pull: As the lithosphere moves away from the mid-ocean it cools and becomes denser. It begins to subduct, as the leading edge begins to sink it pulls the rest of the plate along behind it.