1. Chapter 8 BHS Earth Science
Plate Tectonics
Chapter 8
BHS Earth Science

2. Hollywood’s Version

3. Continental Drift
Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent.
Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.

4. Continental Drift Evidence:
Jig-Saw Fit
Continents fit together like Puzzle pieces
Fossil Evidence
fossils of same age and species were found in connecting bands on different continents
Rock Types and Structure
Similar bands of rocks types and mountain belts connect
Ancient Climates
PANGAEA!

5. Connecting Mountain Ranges

6. Top 100 Greatest Discovery

7. Rejecting the Hypothesis
Most scientists rejected Wegener’s ground breaking hypothesis because he could not provide an explanating of how the plates moved
A NEW THEORY EMERGES!

8. Seafloor Spreading
In Wegener’s theory, continents “plowed” through the sea like bull-dozers.
Not the case. Continents are actually connected to plates, which move
Continents actually move with lithospheric plates that are pushed by Mid-Ocean ridges

9. Harry Hess Discovered “Mid-Ocean Ridges
Spreading centers for tectonic plates
Noticed magnetic stripes on the ocean floor which proved that new crust was being created at these ocean ridges
Provided the mechanism for how the plates moved.

10. Top 100 Greatest Discovery

11. Topographic Map of the World

12. Plate Tectonics
The theory explaining how the movements of earth’s “TECTONIC PLATES” or “moving plates” create the geologic events like earthquakes, volcanoes and tsunamis.
Lithospheric Plates- giant puzzle pieces connecting on the surface of earth.
These sit on top of mantle so they can move around

13. Plate Boundaries Three types: Divergent Boundary Convergent Boundary
Transform Boundary

14. Divergent Boundary Plate moving apart Examples:
Mid Atlantic Ocean Ridge
East Pacific Rise
Plates are being pushed apart… as they are pushed apart, magma rises from the mantle and fills the void.
Mechanism for plate movement

15. Ocean Ridges
Oceanic ridges are continuous elevated zones on the floor of all major ocean basins. The rifts at the crest of ridges represent divergent plate boundaries.

16. Rift Valleys
Tears in the earth
Also caused by Divergent Boundaries

17. Convergent Boundaries
Two plates crashing together
Collliding
Three types:
Continental to Continental
Ocean to Ocean
Ocean to Continental

18. Continent to Continent collision
When two continents collide, you will get mountain ranges
Example: Himalayans (India crashing into Asia)

19. India and Asia

20. Ocean to Ocean Convergance
Two oceanic slab converge together. One is pulled under the other
Often forms volcanoes on seafloor
Volcanic Island Arcs
Aleutian Islands
Alaska

21. Ocean to Ocean Convergent
Aleutian Island, Alaska, US

22. Ocean to Continental Convergance
ALSO KNOWN AS SUBDUCTION ZONE
Oceanic plate is forced down into the mantle beneath a second continental plate
Creates volcanoes and deep ocean trenches
Examples Andes and Marianna Trench
Marianna Trench is deepest place in the WORLD! 35,000 feet deep!!!!!

23. Subduction Zone

24. Subduction Zne

25. Subduction Zone process
Denser ocean slab pulled underneith continent
As it is pulled under, the oceanic crust begins to melt.
When crust begins to melt, magma rises
Magma rises to surface and creates volcanoes

26. Transform Boundaries
Plates grind past each other without destroying or creating new lithosphere
Like cars passing each other on a highway
Creates tremendous earthquakes
Example: San Andreas Fault

27. Transform Boundaries

28. How do Plates Move? The crust lies on top of the mantle.
It is believed that convection currents cause movement in the asthenosphere. Heat rises from interior.
Areas where the asthenosphere is raising causes plates to move apart (diverge) and areas where the asthenosphere is sinking causes plates to move together (converge).

29. Why do plates move? Clear answer is yet unknown
There are theories for “Ridge Push”, “Trench Suction”, and just plain old “Gravity”