1. Plate Tectonics

2. Continental Drift 101

3. Chapter 10-1 Continental Drift
Objectives:
Describe the hypothesis of continental drift.
Identify evidence supporting continental drift.

4. The Theory of Continental Drift
The theory of continental drift, stated by Wegner, a German meteorologist, says that Earth once had a single landmass that broke up into pieces, which have since drifted apart.
Scientists call this giant landmass, Pangaea, which means all Earth.

5. Wegener’s Evidence
Wegener’s evidence for continental drift came form four areas:
Fit of the coastlines
Fossil
Rocks
Climate

6. Fit of the Coastlines
Many of the landmasses, such as South America and Africa, appear to fit together as if they are pieces of a puzzle.

7. Evidence from Fossils
Evidence from identical fossils found in both South America and Africa supports Wegner’s theory.
Fossils of Glossopteris, an extinct plant, found in rocks from South Africa, Australia, India and Antarctica provide support. The seeds of this plant were too large to have been carried by the wind and too fragile to have survived the ocean waves.

8. Antarctica
The presence of Glossopteris fossils in the frozen wasteland of Antarctica also indicate that the climate must have changed greatly. Antarctica must have changed position.

9. Evidence from Rock
An ancient folded mountain chain formed in Africa lines up with matching folded mountains in South America.
Coal field layers found in Brazil line up with coal field layers in Africa.

10. Evidence from Climate
Glacial deposits found in areas of warm climate also provide evidence.
Salt deposits normally formed between 35 and 10 degrees North and South of the equator are found as far north as Michigan.

11. Break Up of Panagaea

12. How did the continents move?
Wegener could not explain how the continents moved. He though they plowed through the ocean floor. It did not seem possible that the continents could plow through the harder basaltic rock of the ocean floor.
Most scientists did not believe his theory until later it was explained how the continents moved.

13. Chapter 10-2 Sea floor Spreading
Objectives:
Explain seafloor spreading.
Recognize how age and magnetic clues support seafloor spreading.

14. Mapping the Ocean Floor
During World War I German scientists introduced the idea of using sound waves to detect submarines. In the 1940s scientists began to use sound waves to map the ocean floor. This is sometimes called echo sounding.

15. Seafloor Spreading
Scientists notice ridges and trenches forming on the seafloor in patterns.
Magnetic strips show where large amounts of iron deposits exist on the seafloor.
Seafloor is constantly growing and reshaping itself.
Sublimation Zones areas where seafloor is pushed under the larger continental crust and destroyed.

16. Chapter 10-3 The Theory of Plate Tectonics
Objectives:
Compare and contrast different types of plate boundaries.
Explain how the heat inside the Earth causes plate tectonics.
Recognize features caused by plate tectonics.

17. Plate Tectonics
In the 1960s scientists developed a new theory that combined continental drift and seafloor spreading.
This new theory was called plate tectonics.
According to this theory the earth is broken into irregularly shaped sections that move on a plastic like layer called the mantle.

18. Composition of Lithospheric Plates
Plates are made of crust and a part of the upper mantle. These two parts combined are the lithosphere. It is rigid and about 100 km thick.
The plastic like layer below the lithosphere is known as the asthenosphere.

19. Seven Lithospheric Plates
The Pacific plate covers 1/5 of the Earth’s surface.
The other major plates are the North American, South American, Eurasian, African, Indo-Australian and Antarctic plates.
There are also smaller plates such as the Caribbean and Arabian plates.

20. Plate Boundaries
Plates move at different speeds and in different directions. Smaller landmasses move more quickly.
In a few cases, the edges of the continents are the boundaries of plates.
Most plate boundaries are on the ocean floor.

21. Types of Plate Boundaries
There are three types of plate boundaries.
Divergent Boundaries
Convergent Boundaries
Transform Boundaries

22. Divergent Boundaries
The first type occurs at mid-ocean ridges. Because the plates move apart, the ridges are called divergent. These boundaries are also called constructive boundaries. The average rate of seafloor spreading is 5 cm/yr.

23. Convergent Plate Boundaries
There are three types of convergent plate boundaries:
Ocean - Ocean
Ocean - Continent
This type of plate boundary has trenches. Because the plates come together at the trenches, these boundaries are called convergent. They are also called destructive.
Continent – Continent
This does not produce a trench but some land is destroyed.

24. Convergent Plate Boundaries
Continental and oceanic plates collide – the oceanic plate is overridden
oceanic plate is forced down into the mantle in a process known as "subduction”
Melting produces magma chambers that break through crust forming a volcano

25. OMG VOLCANOES

26. Transform Boundaries
The third type of plate boundary is formed when plates move side by side. No new plate material is destroyed or made. Earthquakes often occur along strike-slip boundaries, such as the San Andreas Fault.

27. Earthquakes

28. Pacific-North American Plate Boundary
The Pacific Plate is moving in a northwest direction. The North American plate is moving to the southwest.
Eventually the part of California on the Pacific Plate will move up toward Alaska and collide with the Aleutian Islands.

29. Causes of Plate Tectonics
Today most scientist think plates move as convection currents in the mantle circulate.
A convection current is the movement of material caused by differences in temperature. Mantle material close to the core is very hot. Mantle material farther from the core is cooler and more dense. Rising and sinking of magma occurs in a circular motion.

30. Faults When rocks break and move along surfaces, a fault occurs.
Faults interrupt rock layers by moving them out of place.
Entire mountains can form this way and are called fault-block mountains.

31. Evidence of Plate Movement
Magnetic stripes on ocean floor
Volcanoes and earthquakes
Lasers and satellites

32. Hawaiian Islands
The Hawaiian Islands show direction of plate movement as well as the rate of movement in the past.
The Hawaiian Islands formed over a hot spot in the Pacific Plate.
As the plate moves over the hot spot new islands are created with the youngest island being over the hot spot.

33. Possible Changes in Plates
Any change in one plate or boundary affects all the other plates and boundaries. There are many changes that can occur in plates and their boundaries. Continental plates may fuse together. A trench may switch direction and begin to subduct a formerly overriding plate. New divergent boundaries may form in the center of continents. Plates may also be completely subducted and disappear.

34. Prediction of our Future World