PLATE TECTONICS

1. PLATE TECTONICS

2. PLATE TECTONICS • With all our talk of glaciers melting and slowly making the sea swallow our land whole, we have to keep our minds open. • Is it possible for land to grow?

3. PLATE TECTONICS • Of course, it is! • Anyone heard of Hawaii? • Those islands are growing all the time! • The volcanoes release magma which hardens and grows the land.

4. PLATE TECTONICS • It might be easy to think of the earth as a still and dead thing. • It’s not though! The earth is always changing! • Over the years, the earth has been lifted up, pushed down, bent and broken.

5. PLATE TECTONICS • The deepest mine in the world is a gold mine in South Africa and it is 3.8 km deep. • That barely even scratches the earth’s surface. • The core of the earth is over 6000 km deep.

6. PLATE TECTONICS • If we haven’t ever been there how do we know it’s there? • Scientists use two main types of evidence to learn about Earth’s interior. • Direct evidence from rock samples. • Indirect evidence from seismic waves.

7. PLATE TECTONICS • Rock samples are great clues to what’s deep within the earth. • We have drilled up to 12 km below the surface and taken samples. • From these samples, we can make a good guess as to what happens at deeper depths.

8. PLATE TECTONICS • Seismic waves are a bit more interesting. • When an earthquake occurs, it produces what’s called a seismic wave. • By studying the way these travel through the earth, we can discover things about the layers of the earth and the changes in composition among them.

9. PLATE TECTONICS

10. PLATE TECTONICS • The three main layers of the earth are the crust, the mantle, and the core. • These layers vary greatly in size, composition, temperature and pressure.

11. PLATE TECTONICS • Temperature changes as you near the earth’s core. • At first the rock is cool, but about 20 mdown, the rock would begin to get warmer. • The core is the warmest part of the earth. The heat is from the radioactive materials inside the earth and leftovers from the formation of the planet.

12. PLATE TECTONICS • Pressure, as we go deeper into the earth would also increase. • Because there is more rock pushing down on the deeper layers, the pressure increases.

13. PLATE TECTONICS • As far as composition and thickness, let’s discuss that layer by layer. • The Crust is a layer if solid rock that includes both dry land and the ocean floor.

14. PLATE TECTONICS • The crust is the thinnest layer of the earth by far. • You can think of the crust as that paper-thin outer layer of an onion. • In most places, the crust is 5-40 km thick. • It is thickest under mountains and thinnest at the ocean floor.

15. PLATE TECTONICS • The crust beneath the ocean is called oceanic crustand this consists mostly of basalt. • That’s dark rock with a very fine texture. • Continental crust is the part that makes up the continents and consists mostly of granite. • This is rock of light color and coarse texture.

16. PLATE TECTONICS • The layer beneath the crust is called the mantle. • The mantle is a layer of rock that is very hot but still solid. • The mantle is divided into three layers. • All tolled, the mantle is nearly 3000 km thick.

17. PLATE TECTONICS • The outermost layer of the mantle is called the lithosphere. • This is 100 m thick in most places and quite hard. • The middle layer is called the asthenosphere. • This layer is slightly softened by the heat. • The lower layer is called the lower mantle. • This layer is solid again.

18. PLATE TECTONICS • The center of the earth is called the core. • The core is mostly iron and nickel. • The core is made of two layers…the outer core and inner core. • The outer layer is molten metal • The inner layer is solid metal.

19. PLATE TECTONICS • It is the movement of the liquid outer layer of the core that create the earth’s magnetic fields.

20. PLATE TECTONICS • Let’s return to the crust for the next section of our lesson which will be over continental drift. • When North and South America were discovered, it was noticed how neatly the continents could fit together, predominantly South America and Africa.

21. PLATE TECTONICS • It was 1910 before Alfred Wegener, a young German Scientist hypothesized that the continents had indeed once been joined, but just has moved.

22. PLATE TECTONICS • Wegener’s idea became known as continental drift. • He called the supercontinent made up of all our lands Pangaea which literally means “all lands.”

23. PLATE TECTONICS • Over the years, Wegener gathered evidence for his theory. • The evidence he collected included… • Land Features • Fossils • Evidence of Climate Change

24. PLATE TECTONICS • The land features Wegener found were exemplified by mountain ranges. • When he pieced together the maps of Africa and South America, he saw that the mountain ranges line up!

25. PLATE TECTONICS • The fossils Wegener studied were equally eye-opening. • Nearly identical fossils of plants and animals can be found on areas now separated by oceans!

26. PLATE TECTONICS

27. PLATE TECTONICS • The climate change evidence was poignant too. • The fossils and rocks would be different were they in a warmer or colder climate. • Wegener noticed that there were tropical plant fossils on Spitsbergen, an island in the Arctic Ocean.

28. PLATE TECTONICS • Even with all this Wegener’s hypothesis was rejected. • They said he couldn’t provide enough evidence to prove it to be fact.

29. PLATE TECTONICS • The way mountains form is one reason Wegener was shot down. • Scientists assumed at the time that the reason mountains happen was because the earth is cooling and “shriveling up” so to speak. • Wegener said that if this were so, mountains would be everywhere and not in the thin, narrow bands where the really are.

30. PLATE TECTONICS • This argument brought about discussion of plate tectonics. • J. Tuzo Wilson was a Canadian scientist who began to notice cracks in the earth. • His theory was that the lithosphere was broken up into sections called plates.

31. PLATE TECTONICS • Wilson then combined what scientists knew the sea-floor spreading, continental drift and the Earth’s plates into a single theory. • REMEMBER:A scientific theory is a well-tested concept that explains a wide range of observations.

32. PLATE TECTONICS • The Theory of Plate Tectonics states that pieces of the earth’s lithosphere are in slow, constant motion, driven by convection currents in the mantle. • The theory explains the formation, movement, and subductionof Earth’s Plates.

33. PLATE TECTONICS • The edges of the plates are called faults. • There are three types of these boundaries. • Convergent • Divergent • Transform • Different types of movement occur at each type of boundary.

34. PLATE TECTONICS • A divergent boundary is where two plates come apart. • Most of these are on the ocean floor. • When they occur on land, the gap is called a rift valley.

35. PLATE TECTONICS • A convergent boundary is where two plates come together or converge. • When plates collide, the denserof the two will slide under the less dense one.

36. PLATE TECTONICS • Since oceanic crust is more dense than continental crust, oceanic crust will always sink beneath. • When two continental crust plates meet, no subduction takes place. • Instead both plates smash upwards and a mountain range is formed.

37. PLATE TECTONICS • Transform boundaries are ones where two plates slide past each other. • The grinding created of the two plates is what causes earthquakes. • Crust is neither created or destroyed here.

38. PLATE TECTONICS • Plates are moving all the time. • Now, we have evidence that, before Pangaea, there were other supercontinents. • Perhaps one day, North America and Europe will once again be next-door neighbors!!!