1. Earth Science
Plate Tectonics
Chapter 12

2. The Structure of the Earth
Earth was molten ball (liquefied rock) that cooled – denser/heavier materials sank towards interior and lighter/less dense ones floated to surface
Lighter materials – silicon, oxygen – SILICATES  CRUST (upper mantle – lithosphere)

3. The Structure of the Earth
Crust – made of solid rock
Crust & Uppermost mantle – lithosphere
Upper mantle but below lithosphere - asthenosphere
2 types of tectonic plates – continental plates (granite) and ocean plates (dense rock)

4. The Structure of the Earth
Crust:
solid rock plates which float on the liquid mantle.
Mantle:
thickest layer, fluid, flows like “thick toothpaste”
Outer Core:
liquid, very hot, under fairly high pressure, mostly Fe & Ni.
Inner and outer core rotate at different speeds which may be responsible for Earth’s magnetic field
Inner Core:
solid, under high pressure, mostly Fe.

5. The Structure of the Earth
The rock plates are called “tectonic plates” and they are always in motion.
The reason for this is the mantle’s
CONVECTION CURRENTS
Crust
Molten rock near the core heats up and rises. As it reaches the crust it cools and moves back down to the core, creating a circular current.
Hotter less dense material rises
Mantle convection – driving force behind plate movement
Radioactive decay of elements like uranium heats up the mantle
Liquid
Mantle

6. Tectonic plates Convergent boundary – tectonic plates collide
Divergent boundary – tectonic plates are spreading apart
Transform fault – a break in the rock layers due to movement of plates
Transform boundary – regions where rocks slide past rock but no mountains or volcanoes form

7. The Structure of the Earth
Mantle convection – ridge as magma reaches earths surface at spreading centers
If this happens on land – RIFT VALLEY
Magma cools and pushes older material aside – RIDGE PUSH
Subduction at TRENCH, pulls plate w/ it (Slab PULL)

8. The Structure of the Earth
Magma pushed through spreading centers – cools and creates new rock which pushes older material away from ride – RIDGE PUSH

9. The Theory of Plate Tectonics
Describes the idea that the Earth’s outer rigid shell is made up of moving plates
the movement is responsible for volcanoes and earthquakes, mountain building, and ocean ridges.
the plate boundaries have “fault zones” around them where many volcanoes & earthquakes occur.
Transform Fault zone – zones where rock slides past rock but no mountains or volcanoes form at a plate boundary
Can create breaks in rock layers

10. The Theory of Plate Tectonics
there are 3 kinds of faults (plate boundaries)
colliding (moving together) (convergent)
rifting (tearing apart) (divergent)
sliding sideways (transform)
The way in which tectonic plates interact depends on two main factors:
The type of plate
The direction of plates moving in relation to one another

11. Examples: Convergent Boundary Oceanic - Continental
Deep underwater valley – trench (Marianas trench is 10.9 km deep)
As subducting plates moves down – parts melt off and turn into rock – magma can come to surface and create volcano
Juan de Fuca plate & North American Plate (continental) – created chain of volcanoes in North America
Creates coastal mountains, often with a volcanic belt as oceanic plate is subducted.

12. Examples: Convergent Boundary Oceanic - Oceanic
Subduction occurs then cooling will make one plate denser – denser one slides down – can produce chain of volcanoes
The denser plate moves down and a chain of volcanoes are produced.

13. Examples: Convergent Boundary Continental - Continental
Plates similar densities so no subduction – edges fold and crumple – collision of Indian & Asian continent
The two plates fold and crumple, creating mountain ranges.

14. Examples: Divergent Boundary
Creates mountain ranges
Creates new seafloor or land called rifts or ridges that are basically new mountains.

15. Examples: Transform Boundary
Transform boundary – plates slide past each other
If breaks in rock occur at boundary – transform faults
Rocks slide past each other and faults are created. No volcanoes or mountains are formed.

16. Assignment
Homework:
Workbook Pages 210, 212, 218, 219