1. Plate Tectonics
Evolution of the Earth

2. Cracks in the Earth’s Crust
The crust, when it is solid, acts as a heat insulator for the hot interior of the Earth.
The molten material in the mantle, magma, below the crust builds up tremendous heat and pressure.
The magma creates convection currents and rises to the surface.
These currents can crack the crust (both oceanic and continental)!

3. Tectonic Plates
These cracks separate the crust into plates (huge sections of the Earth that moves relative to each other).
Lithosphere is responsible for tectonic plates because it adheres the crust to the mantle.

4. Plate Boundaries Convergent Boundaries
Subduction – when one oceanic plate plunges beneath another
Crust enters mantle, pressure cracks crust
Volcanoes
Ocean trenches
Continental Collision - continental plates move toward one another
The crust moves upward, folds and buckles and breaks
mountains
Divergent Boundaries – plates move away from each other
Seafloor spreading
Mid-ocean ridges
Transform fault – plate moves sideways from each other, slide past each other
earthquakes

5. Subduction

7. Convergent Plates

8. Convergent Plates

9. Seafloor Spreading Magma rises to the oceanic crustal surface
forms mid ocean ridges.
As the lava cools, it forms new seafloor and features: rift valleys; seamounts; abyssal hills (volcanic peaks)
As new material reaches the surface, the plates are pushed apart

11. Seafloor Spreading cont.
Earth’s longest mountain chain
47,000 miles long running down the middle of the Atlantic Ocean (surfacing at Iceland), around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean.
Running along the top of this chain of mountains is a deep crack, called a rift valley. It is here that new ocean floor is continuously created.
As the two sides of the mountain move away from each other, magma wells up from the Earth's interior. It then solidifies into rock as it is cooled by the sea, creating new ocean floor.
The mapping of the seafloor also revealed that these huge underwater mountain ranges have a deep trench which bisects the length of the ridges and in places is more than 2000 meters deep.
Seismic studies show that the mid-oceanic ridges experience an elevated number of earthquakes. All these observations indicate intense geological activity at the mid-oceanic ridges.
The speed at which new ocean floor is created varies from one location on the ocean ridge to another.
Between North America and Europe, the rate is about 2.2 inches/year
At the East Pacific rise, which is pushing a plate into the west coast of South America, the rate is 12.6 inches/year

12. Transform Plates

13. Transform Plates
San Andreas
Fault

15. Why do the Plates Move?
No single idea explains everything but we can identify several forces that contribute to the movement of the plates.
Slab pull
The sinking of the cooled dense oceanic plates pulls on the rest of the plate
Ridge rises
The material deposited on the top of the ridge slides downs from the rise pushing on the plate
Convection
Movement within the mantle could be part of the driving force behind the motion of the plates.

16. Tectonic Plates
Earth’s crust is broken into about 19 pieces

17. Earthquakes
Tidal waves or Tsunamis result when a large section of the sea floor
suddenly moves and therefore displaces a massive amount of water.

18. Earthquakes
Location of worldwide earthquakes

19. Tectonic Plates
Earthquakes

20. Tectonic Plates
Volcanoes

21. Pangea What is Pangaea? Pangaea was a super continent at one time.
200 mill years ago, plates shifted enough to cause movement.
Scientists use the similarity of rock types and fossil types that date to the same age to support their theory that the continents were connected to form a super continent.

22. Pangea

23. Pangea
The break up
of Pangea

24. Where are we going? We appear to be headed for another super
continent as North America, South America,
Asia and Australia converge in the
ever shrinking Pacific Ocean