1. The Theory of Plate Tectonics
Objectives: (copy me down in your HSN)
What is plate tectonics vs. continental drift?
Where does the FORCE come from to move the tectonic plates?
Describe the three types of plate boundaries.

2. Wegner’s Further Evidence:

3. Let’s review: Tech Terms: (copy these down)
plates – separate sections of the lithosphere.
plate tectonics – a geological theory that states that pieces of the Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle.

5. Sea Floor-Spreading
2. mid-ocean ridge – longest chain of mountains extending into all of Earth’s oceans, that curves like the seam of a baseball along the sea floor.

7. These plates are created by 3
These plates are created by 3. faults – breaks in Earth’s crust where plate boundaries form.
The Theory of Plate Tectonics: What are the boundaries and how do they move?
3 Different ways!

8. What are Three Possible Driving Forces of Plate Tectonics?

9. 4. divergent boundary – the place where two plates move apart, or dive away (most occur at the mid-ocean ridge from seas floor spreading).
5. Example: Sea floor spreading- the process that adds new material to the ocean floor at the mid-ocean ridge..

12. Divergent boundaries…
6. Example: rift valley – develops
on land, where two plates diverge.

14. Tech terms, copy these down!
7) convergent boundary – the place where two plates come together, or collide. (the density of the plates dictates which one comes out on top).
Oceanic crust (basalt rock) is more dense
Continental crust (granite rock) is less dense

15. Subduction zones occur at convergent boundaries and create trenches

16. Examples:
8. subduction – when the ocean floor sinks beneath a deep ocean trench and gets swallowed by the mantle.
Sea Floor Spreading& Subduction:
Plate Tectonics inside the mantle again! (2 min)

17. 9. deep ocean trench – this forms from subduction (the oceanic crust bends downward forming a deep underwater canyon on the ocean floor).

18. deep ocean trench close to home

20. 3 “Big Effects” of Subduction and Seas floor Spreading:
10. Evidence of Plate tectonics: Sea-floor spreading and subduction can change the size and shape of the oceans.
The Atlantic Ocean is expanding.
The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller.

21. Atlantic Ocean is expanding

22. Pacific Ocean is shrinking

23. 3 “Big Effects” of Subduction and Seas floor Spreading:
10. Evidence of Plate tectonics: Sea-floor spreading and subduction can change the size and shape of the oceans.
The Atlantic Ocean is expanding.
The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller.

24. 11. transform boundary –
a place where two
plates slide past
each other in
opposite directions.

25. Transform boundaries do not create landforms
Transform boundaries do not create landforms. They do, however, destroy land!

26. See the offset from the
Transform boundary?

27. So what will happen as these plates in the ocean floor continue to spread?
Earth 100 Million Years from now
Convection Currents in the Earth. One more time, a different way!
Plate tectonics on a cocoa earth - YouTube

28. Further Evidence for Sea-Floor Spreading:
11. Magnetic Reversals-
Molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals. These mineral grains contain iron and are like compasses. They change Earth’s magnetic poles!!

29. Magnetic reversals in oceanic crust are shown as bands
Magnetic reversals in oceanic crust are shown as bands. Light blue is when the poles have normal polarity. Dark blue indicates reverse polarity.

30. Magnetic Reversal videos:

31. The polarity of Earth’s magnetic field changes over time.