1. 2 Plate Tectonics

2. Main plates of the earth

3. Chapter 2: Plate Tectonics
Theory of plate tectonics
“Plate Tectonics” explains why the plates of the earth are moving.
The main idea (theory) was proposed by Alfred Wegener in 1912.
Earth’s crust consists of plates that move or float on the mantle
Movement is caused by convection currents in the mantle.
Plates diverge, converge or slide past each other.

4. Chapter 2: Plate Tectonics
Magma Convection currents
Causes the movement of plates
Magma heats; rises and moves towards the upper mantle
The magma flows sidewards, then cools and sinks.
Plate moves with sinking magma
Circular movement fuels plate movement

5. Chapter 2: Plate Tectonics
Sea floor spreading
New rock is formed where plates were split apart (Iceland!!)
Ocean floor widens; magma rises from within the mantle and fills the opening
Magma cools; new ocean floor formed
New sea floor youngest at the mid-ocean ridge
The rocks found further from the plate divide are older so older rocks are found closer towards continents.

6. Red represents the newest crust of the earth
Red represents the newest crust of the earth. The further from red the older the crust. Where is Ireland?

7. Chapter 2: Plate Tectonics
Theory of continental drift
Suggests that the continents are moved across the planet by convection currents
Drifting of the continents is still occurring today
Continents were once all joined together in one single landmass known as Pangaea. ……..a supercontinent.
Approximately 200 million years ago Pangaea began to break apart
The continents were fuelled by the convection currents and so they began to drift apart (pangea divided into Laurasia and Gondwanaland…until these broke further apart into todays continents.)

8. Chapter 2: Plate Tectonics
The process of subduction
Continents collide
Oceanic plate is heavier than the continental plate
Ocean floor pulled down into the mantle
Subduction occurs

9. Chapter 2: Plate Tectonics
Plate boundaries
There are three types of plate boundaries:
Divergent (boundaries of construction)
Convergent (boundaries of destruction)
Conservative (passive boundaries)

10. Chapter 2: Plate Tectonics
1. Divergent (constructive boundaries)
New crust is formed
Mid-ocean ridges created (Mid-Atlantic Ridge)
Plates separate and move away from each other
Example: American and Eurasian plates

12. Chapter 2: Plate Tectonics
2. Convergent (boundaries of destruction)
Three types of destructive boundaries:
Oceanic-continent: where an ocean and continental plate collide
Oceanic-oceanic: where two ocean plates collide
Continent-continent: where two continental plates collide
Heavier oceanic plate subducts
Magma rises to create volcanoes at the continental plate
Continental plate is buckled and fold mountains form
Heavier, older plate dips
Subducted beneath lighter, younger plate
Deep sea trench may develop
Neither plates sink on collision
Lithosphere subducts
Continental crusts buckle
Formation of fold mountains

13. Chapter 2: Plate Tectonics
3. Conservative (passive boundaries)
crust is neither created nor destroyed
Plates slide past each other
The line along which the plates slide is known as a fault line
Known as transform faults
e.g. the San Andreas Fault in California

14. The position of Ireland

17. Chapter 2: Main details
Who proposed the Theory of Plate Tectonics?
What is the main idea of this theory?
What causes the plates of the earth to move?
What causes magma to move in the mantle?
What was Pangea?
What proof do we have that the continents of the earth were once all joined together?

18. 7. What are the three types of plate boundary?
8. Name examples of each plate boundary?
9. What feature is generally found at each boundary?
10. Can you name a famous world feature found at each of the main boundary types?