1. 21/09/2018
Plate Tectonics The idea of continental drift is now referred to as plate tectonics. How can the continents move?

2. Remember the Earth’s structure
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A thin crust km thick
A mantle – has the properties of a solid but it can also flow
A core – made of molten nickel and iron. Outer part is liquid and inner part is solid
The average density of the Earth is much higher than the crust, so the inner core must be very dense

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

4. Words – radioactive, crust, convection, tectonic, year
Movement of the Crust
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The Earth’s LITHOSPHERE (i.e. the _______) is split up into different sections called ________ plates:
These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core.
Words – radioactive, crust, convection, tectonic, year

5. The Earth’s Plates

6. Names of Plates
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7. Tectonic theory
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People once thought that the oceans and the continents were formed by shrinkage from when the Earth cooled down after being formed.
Alfred Wegener proposed something different. Consider Africa and South America:
These continents look like they “fit” together. They also have similar rock patterns and fossil records. These two pieces of evidence led me to believe that there was once a single land mass. This is my TECTONIC THEORY.

8. Fit of Continents Across the Atlantic

9. Gondwana – 200 million year ago
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10. Forming mountains
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The formation of mountain ranges can be explained by tectonic theory. Consider the Himalayas at the top of India:
This is where India is now
This is where India was millions of years ago
The intense heat and pressure from this process causes the rocks to change structure into metamorphic rocks.

12. Tectonic theory
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The Evidence:
Some continents look like they used to “fit” together
Similar rock patterns and fossil records
The Problems:
Wegener couldn't explain how continental drift happened so nobody believed him
The Answer:
Scientists discovered 50 years later that the Earth generates massive amounts of heat through radioactive decay in the core. This heat generated convection currents in the mantle causing the crust to move
We also now know that the sea floor is spreading outwards from plate boundaries
Conclusion – scientists now believe Wegener’s Tectonic Theory

13. What it looked like in the past
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14. How Plates Move

15. What Drives It? Convection Currents in the Mantle

16. The Plate Tectonics Model

17. Movements of the plates
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When the plates moves three things can happen:
1) Plates move past each other, causing earthquakes
2) Plates can be pushed apart to form a rift. In the rift, volcanoes erupt forming new rock as the magma solidifies. Undersea rifts have undersea volcanoes. Eg. African Rift Valley and the Mid-Atlantic Ridge system -this is called sea floor spreading.
3) Plates can also push together either buckling and joining both plates (for example the Southern Alps) or with one plate "diving" beneath the other (called subduction). Subduction is occurring east of the North Island and south of the South Island. This causes volcanoes and earthquakes.

18. Tasks to complete Describe what is meant by the term Plate Tectonics
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Describe what is meant by the term Plate Tectonics
Copy and complete the sentences on Slide 4 – Movement of the Crust
Describe the three things that can happen when plates move
Print off a map of the world showing the tectonic plates and label the two plates related to New Zealand