1. How do tectonic plates move?
Notes
How do tectonic plates move?

2. Continental Drift
Alfred Wegener (1915)
Continental Drift
Pangaea

3. Evidence for continental drift:
Fossils
Climate
Geology

4. ? Problem: Wegener could not explain HOW the continents moved.
Continental Drift ?
Problem: Wegener could not explain HOW the continents moved.

5. Sonar Technology (World War I)
New Evidence in the 1950’s
Sonar Technology (World War I)
Uses sound to measure distance underwater
Like echolocation in bats!

6. Scientists used sonar to map the ocean floor.
New Evidence in the 1950’s
Scientists used sonar to map the ocean floor.
Led to the discovery of the mid-Atlantic ridge.

7. Other discoveries: Underwater volcanos Geothermal vents Hot springs
New Evidence in the 1950’s
Other discoveries:
Underwater volcanos
Geothermal vents
Hot springs
Deep ocean trenches

8. Plate Tectonics
The theory of plate tectonics builds on Wegener’s ideas but also explains HOW the plates and continents move.

9. Plate Tectonics
Harry Hess ( )
Discovered that rock on the seafloor is younger near a mid- ocean ridge and older further away from the ridge

10. Plate Tectonics

11. Plate Tectonics
New crust is being created in the middle of a mid-ocean ridge, where two tectonic plates are being pushed apart.

12. Cracks in Earth’s crust are the tectonic plate boundaries.
Plate Tectonics
Cracks in Earth’s crust are the tectonic plate boundaries.
Magma rises through the crack, pushes the two plates a little further apart, and cools to form new crust.

13. Driving Forces
Remember-tectonic plates float on the asthenosphere-a layer of hot, soft rock.

14. Convection: transfer of (heat) by movement of a substance.
Driving Forces
Convection: transfer of (heat) by movement of a substance.
Convection is what happens when you boil a pot of water.

15. The water at the bottom heats up, becomes less dense and rises.
Driving Forces
The water at the bottom heats up, becomes less dense and rises.
Near the surface, it cools, becomes more dense, and sinks.

16. Driving Forces
Rock in the asthenosphere acts the same way as a boiling pot of water-it moves by convection.

17. Driving Forces
When this rising and sinking repeats, it creates a circular pattern called a convection current.

18. Driving Forces
The movement of the mantle is much slower than a pot of boiling water-only a few centimeters per year!

19. Driving Forces
The movement of the asthenosphere is like heavy boxes on rollers-but moving very, very slowly.

20. Driving Forces
Slab Pull: when gravity pulls the edge of a cool plate into the asthenosphere.

21. Driving Forces
Ridge Push: when material from a mid-ocean ridge slides downhill from the ridge.

23. Putting it All Together
There are several tectonic plates on Earth.
One plate cannot shift without affecting the others nearby.
Two neighboring tectonic plates can either move apart, move together, or slide past one another.

24. Putting it All Together
Divergent boundary: plates move apart

25. Putting it All Together
Convergent boundary: plates move toward each other

26. Putting it All Together
Transform boundary: plates slide past each other