1. Unit 4: Earth Science
How can Plates Move?

2. Layers of the Earth
Crust
Mantle
Outer core
Inner core
Not to scale

3. Crust Two types: Continental crust Oceanic crust
Outermost layer, relatively solid, brittle rock 
Two types:
Continental crust
approx. 50 km thick
made from less dense type of rock called granite
Oceanic crust
approx. 10 km thick
made from denser rock called basalt
Not to scale

4. Mantle Thickest Layer: 2900 km thick
dense rock, rich in iron, magnesium and silicon.
Uppermost part (Upper Mantle) is solid, more cool and brittle, 
Lower Mantle is molten rock, still solid, dense, flows like toothpaste

5. Outer Core
2150 km thick
Made up of liquid iron and nickel
Inner Core
1300 km thick
solid iron and nickel (due to tremendous pressure)
Extremely hot 5,500°C

6. Tectonic Plate Layers
In the Plate Tectonic Theory, rocks near the surface of the earth can be divided based on their characteristics.
Like a hard boiled egg with moving broken shell pieces, Earth’s outer layer is composed of several large rigid but mobile chunks of rock (Tectonic Plates).
TECTONIC PLATES are made up of crust and uppermost mantel (Lithosphere)
Like a hard boiled egg with moving broken shell pieces, Earth’s outer layer is composed of several large rigid but mobile chunks of rock (Tectonic Plates). Made up of crust and uppermost mantel = lithosphere km thick. 12 major plates and many smaller ones.
Heat that keeps asthenosphere molten comes from radioactive elements

7. Tectonic Plates are made of the Lithosphere
LITHOSPHERE is an outer layer of rock composed of crust and top part of upper mantle
Makes up the
tectonic plates
km thick
Plates float and move on the asthenosphere
Like a hard boiled egg with moving broken shell pieces, Earth’s outer layer is composed of several large rigid but mobile chunks of rock (Tectonic Plates). Made up of crust and uppermost mantel = lithosphere km thick. 12 major plates and many smaller ones.
Heat that keeps asthenosphere molten comes from radioactive elements

8. ASTHENOSPHERE:
molten layer in upper mantle beneath plates
So hot it behaves like plastic, less rigid, flows like toothpaste

10. Questions
Tectonic plates are composed of which parts of Earth’s layer?
What are two types of crust?
Describe two features of each.
1. Lithosphere – crust and upper part of mantle
2. two types of crust: oceanic (thinner, more dense), continental (thicker, less dense)

11. How are plates able to move?

12. Plate Movement
Tectonic plates make up the lithosphere (crust and upper portion of mantle), which floats on the asthenosphere (molten, mantle).
Tectonic plates are all moving at the same time

13. Plate Movement Variable temperature causes convection currents
Convection demo
See pages
(c) McGraw Hill Ryerson 2007

14. The Earth’s Temperature
Temperature increases the deeper you go (about 1oC for every 40 m of depth)
Beneath the crust, this temperature rise gradually slows, until a core temperature of about 7000oC is reached.

15. Where does the heat come from?
radioactive decay
friction between rock masses in the crust and mantle;
heat left over from planetary formation.

16. Mantle Convection
Molten rock called magma heats up near Earth’s core, causing it to becomes less dense and therefore rises.
As it gets farther from the core, it cools, becoming more dense, and sinks. 
This cycling is called a convection current. 
Tectonic plates move because of convection currents in the semi-fluid layer of rocks beneath the plates (the ‘mantle’);

17. Mantle Convection:
As magma moves, it drags the tectonic plates above with it.
Rising magma pushes plates apart at spreading centers in oceans
This rotation causes movement of the plates.

18. How can we know how hot it is?

19. How deep can we go?

20. Mantle Convection Demo

21. Homework
Page 3-4 of package

22. Ridge Push
Rising material spread out as it reaches the upper mantle. This cause the lithosphere to lift and push tectonic plates apart at divergent plate boundaries (spreading center). Spreading ridge (in ocean), Rift Valley (land)

23. Slab Pull
Slab Pull – as the leading edge of a subducting plate sinks, it pulls the rest of the plate with it at convergent plate boundaries.
Gravity and convection assist this movement.

24. How deep can we dig?