2. Plate Tectonics

3. What is Plate Tectonics
The Earth’s crust and upper mantle are broken into sections called plates
Plates move around on top of the mantle like rafts

5. Layers of the Earth Crust Mantle Inner core Outer Core Solid Liquid
Lithosphere
Athenosphere
Inner core
Solid
Outer Core
Liquid

6. What is the Lithosphere?
The crust and part of the upper mantle = lithosphere
100 km thick
Less dense than the material below it so it “floats”

7. What is the Asthenoshere?
The plastic layer below the lithosphere = asthenosphere
The plates of the lithosphere float on the asthenosphere

9. 2 Types of Plates
Ocean plates - plates below the oceans
Continental plates - plates below the continents

10. Questions... What is the theory of plate tectonics?
What is the lithosphere?
What is the asthenosphere?
What is the connection between the two?
What are the two types of plates?

11. Causes of Plate Tectonics

12. Convection Currents
Plates move by the transfer of heat through heated material.
Hot magma in the Earth moves toward the surface, cools, then sinks again.
Creates convection currents beneath the plates that cause the plates to move.

14. Questions... What causes plates to move?
How is a convection current formed?

15. Plate Boundaries

16. Major Plate Boundaries
Earth has 6 major plate boundaries
Eurasian
N. American
Pacific
S. American
African
Antarctic

17. Plate Boundary Types

18. 1. Divergent Boundaries  
Boundary between two plates that are moving apart or rifting
 
RIFTING causes SEAFLOOR SPREADING
At the mid-ocean ridge moves 6 cm/year

19. Features of Divergent Boundaries
Mid-ocean ridges
rift valleys
fissure volcanoes

23. 2. Transform Fault Boundaries
Boundary between two plates that are sliding past each other
Moving in opposite directions
Moving in same directions at different speeds
EARTHQUAKES along faults
Ex: San Andreas fault in CA

25. San Andreas Fault, CA

26. 3. Convergent Boundaries
Boundaries between two plates that are colliding
 
There are 3 types…

27. Type 1 Ocean plate colliding with a less dense continental plate
Subduction Zone: where the more dense plate slides under the less dense plate
VOLCANOES occur at subduction zones
Earthquakes are common

29. Andes Mountains, South America

30. Type 2 Ocean plate colliding with another ocean plate
The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH
May form volcanoes a.k.a. volcanic island arc

32. Aleutian Islands, Alaska

33. Type 3
Two continental plates collide: the Continental rocks buckle & rise
Have Collision Zones:
a place where folded & thrust faulted mountains form
Earthquakes are common
Little volcanic activity
Continental motion occurs 1-5 cm/year

36. Questions... What are the three types of boundaries?
What direction do plates go for each?
Which boundary has a subduction zone…what occurs at a subduction zone?

37. Alfred Wegener
In 1915, German geologist Dr. Alfred Wegener proposed an idea called the Theory of Continental Drift.
Said all continents were joined together about 250 million years ago as a supercontinent Pangea (“all land”).
Eventually Pangea split and moved into current positions

38. Wegner’s Clues or Evidence…..
Shape of the continents –
They seem to fit together as one big puzzle….

39. Clues or Evidence continued…
Fossil evidence

40. Clues or Evidence continued…
Climate (Glacial Deposits)..

41. Clues or Evidence continued…
Rocks - similar mountain ranges found on different continents separated by oceans…

42. Evidence
A system of underwater mountain chains or mid-ocean ridges, rise thousands of meters above ocean floor
Caused by plate movement called sea-floor spreading at a divergent boundary
Youngest ocean floor rocks – near mid ocean ridges
Oldest near the edge of the continents
When the sea floor reaches a continental boundary, it is forced downward beneath the continental, called a sea floor trench