1. Theory of Plate Tectonics
Ch.7.3 (New Book)
Theory of Plate Tectonics

2. The Theory of Plate Tectonics
Objectives: (copy me down in your IAN)
What is plate tectonics?
Where does the FORCE come from to move the tectonic plates?
Describe the three types of plate boundaries.
4. Review, what are subduction zones?

3. Let’s Read more about it!
p out loud,THEN:
Answer, how are tectonic plates like ice cubes in a punch bowl?
Let’s compare your tectonic plate maps. (pic on next page)
How many plates are covered in BOTH land and water?

4. Open to p. 194 (New Book) and finish drawing your plate maps in your IAN. Ocean floor blue, land green or brown, and tectonic boundaries in RED!

5. Oceanic and Continental Crusts

6. 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.

7. Now let’s create new maps in our IAN.
Take out the new map from your blue tub. Using p complete the instructions on this new map. An example picture is on the next page!

8. The 10 top Tectonic Plates!

9. 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?
Read aloud p and discuss.

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

11. Subduction zones occur at convergent boundaries and create trenches

12. divergent boundary – the place where two plates move apart, or dive away (most occur at the mid-ocean ridge).
rift valley – develops on land, where two plates diverge.
Read and discuss the picture at the bottom of page

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

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

17. See the offset from the
Transform boundary?

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

19. deep ocean trench close to home

20. 9. subduction – when the ocean floor sinks beneath a deep ocean trench and gets swallowed by the mantle.

21. Sea-floor spreading and subduction can change the size and shape of the oceans.

22. Don’t forget Sea Floor Spreading!
3 “Big Effects”
Sea-floor spreading and subduction can change the size and shape of the oceans.
The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller.
The Atlantic Ocean is expanding.

25. Further Evidence for Sea-Floor Spreading:
Magnetic Reversals!
The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals. These mineral grains contain iron and are like compasses.
They align with the magnetic field of the Earth. When the molten rock cools, the record of these tiny compasses remains in the rock.

26. This record is then carried slowly away from the spreading center of the ridge as sea-floor spreading occurs.
As you can see in Figure 5, when the Earth’s magnetic field reverses, the magnetic mineral grains align in the opposite direction.

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

28. The new rock records the direction of the Earth’s magnetic field
The new rock records the direction of the Earth’s magnetic field. As the sea floor spreads away from a mid-ocean ridge, it carries with it a record of magnetic reversals.
This record of magnetic reversals was the final proof that sea-floor spreading does occur.

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.