1. Plate Tectonics

2. Theory of Plate Tectonics
Theory of Plate Tectonics-Theory that states the earth’s crust is broken into plates that float on lower mantle
Theory combines the theories of continental drift and sea floor spreading
It states how and why continents move
Continents move because they are carried along on moving plates

3. Continental Drift
Continental Drift-Idea that states that continents were once a giant landmass, and broke into pieces that moved to the positions they are in today
A continent is a large landmass
Pangaea-giant landmass that split apart to form today’s continents

4. Crustal Plates
Crustal Plates-large pieces of the solid part of the earth
Most scientist think that the crust of the earth and solid part of the mantle are broken into crustal plates
Most plates are made up of oceanic and continental crust
Largest plate is the Pacific plate

5. Floating Plates Crustal plates float on the lower part of the mantle
Part of the mantle is made up of rock that flows like thick liquid
Continents and oceans are carried on plates

6. Formation of New Sea Floor
Sea-floor spreading-process that forms new sea floor.
Oceanic crust near the mid-ocean ridge is younger than ocean crust farther away
Magma cools forming a new crust on both sides of the ridge and pushes the sea floor out

7. Evidence of Sea Floor Spreading
The earth has a magnetic field
The magnetic field of the earth has changed throughout the earth’s history
Some minerals have magnetic properties
On sea floor there are stripes of rock with magnetic particles pointing north and magnetic particles pointing south

8. Mid-Ocean Ridges Mid-Ocean Ridge-Underwater mountain chain
Some of the largest mountain ranges and tallest mountains are located under the ocean
Peaks of some of these mountains form islands
Mid-Atlantic Ridge runs down the middle of the Atlantic Ocean

9. Subduction Zone
Subduction Zone-Place where old crust is pushed down into a trench
Older oceanic crust is pushed down into the mantle
Mantle-layer of the earth below the crust
There is volcanic activity near subduction zones
Ring of Fire around the Pacific Ocean has many subduction zones

10. Rift Valley
Rift Valley-Deep crack running down the center of the mid-Atlantic ridge
Magma pouring out of the rift hardened and formed a broad valley with steep sides
Scientist discovered that a lot of earthquakes and volcanic activity take place along mid-ocean ridges

11. Trenches Trench-long, V-shaped valley
Trenches are the deepest parts of the ocean
Most trenches are found in the Pacific Ocean
Located along the coasts of continents and near strings of islands
Many trenches are along the Ring of Fire

12. Disappearing Crust
Scientist believe that old oceanic crust is pushed into ocean trenches where it is changed to magma
If the crust were not being destroyed, the earth would be getting bigger
Crust pushed deep enough, the rocks of the crust melt

13. Convection Currents
Convection Currents-Movement of gas or liquid caused by changes in temperature
Warm air rises and cool air sinks to take its place
Hot water rises and cool water at the top ends up sinking

14. Inside the Mantle
Mantle rock close to the core, or center of the earth, is hot
Scientist believe that giant convection currents in the earth’s mantle cause the movement of crustal plates
Hot mantle rock rises and cooler rock sinks deeper in the mantle

15. The Restless Earth Crustal plates move in different ways
Crustal plates move toward each other, move apart, or slide past each other
Oceanic crust is pushed under continental crust
Oceanic crust is pushed into the mantle

16. Earthquakes
Many earthquakes are caused by the movement of plates at a fault
Two crustal plates slide past each other
Movement of crustal plates sliding past each other cause the earthquake
San Andreas Fault-California

17. Mountain Building
Mountains are formed when two plates collide and oceanic crust pushes down under continental crust
Two crustal plates carrying continents may collide without one plate being pushed down under the other
Himalaya Mountains are formed from this method

18. Volcanoes Magma Chamber-Underground pocket of molten rock
At subduction zones, friction between oceanic crust and the continental crust produces great heat
Heat melts the rocks in crust and forms magma
When magma reaches surface volcano forms