CONTINENTAL DRIFT AND PLATE TECTONICS

1. CONTINENTAL DRIFT AND PLATE TECTONICS THE SHAPING PROCESSES OF OUR EARTH

2. CONTINENTAL DRIFT • “Father” of this theory is Alfred Wegener.

3. Untold Tragedies of Continental Drift!!

4. CONTINENTAL DRIFT • Wegener published his belief that the Earth’s continents were once all joined together in a super continent called Pangaea which means “all land”, in 1915. He then theorized that Pangaea broke apart and the continental pieces “drifted” over time into their present location.

5. PANGAEA

6. CONTINENTAL DRIFT

7. ANOTHER VIEW OF DRIFT

8. WHAT EVIDENCE DID WEGENER HAVE? • Wegener provided four main pieces of evidence to support his theory that the continents had been drifting over time.

9. 4!!

10. 1. JIGSAW PUZZLEadd to handout • Wegener noticed that if we could move present day continents around, several continents look like they would fit together like pieces of a jigsaw puzzle.

11. 1. JIGSAW PUZZLE

12. 2. FOSSILS add to handout • Wegener also found fossils of the same plants and animals on different continents now separated by vast oceans. They could only be found this way if the continents had once been joined together.

13. 2. FOSSILS

14. 3. ROCK SEQUENCEadd to handout • Wegener also found that mountain ranges have a similar sequence of type of rock and age on both sides of the Atlantic Ocean, suggesting they were once part of the same mountain range.

15. 3. ROCK SEQUENCE

16. 4. GLACIAL SCARSadd to handout • Wegener found evidence of glacial scars left behind by giant ice sheets from the same time period in Southern Africa, India, Australia, Antarctica and South America.

17. 4. Glacial Scars Now... Then…

18. WHAT COULD MOVE THE CONTINENTS?

19. WEGENER’S WEAKNESS • Unfortunately for Wegener, he could not explain what force was powerful enough to move entire continents around the planet to his scientific peers, so he did not get much support for his theory on continental drift.

20. WEGENER’S EXPEDITION

21. WEGENER’S WEAKNESS • Alfred Wegener died on expedition in Greenland in 1930still searching for answers to the question of what force could be responsible for the movement of the continents.

22. ALFRED WEGENER 1880 - 1930

23. GET READY TO BOOGY!http://www.youtube.com/watch?v=T1-cES1EktoReview:http://www.youtube.com/watch?v=_5q8hzF9VVE (11 minutes)

24. Though several scientists contributed to this theory, the “father” of the Plate Tectonic theory was J. Tuzo Wilson, a Canadian geophysicist… THEORY OF PLATE TECTONICS

25. J. Tuzo Wilson 1908-1993(“Father” of Plate Tectonics)

26. THEORY OF PLATE TECTONICS • Advances in sonar and echo sounding technology in the 1960’s led to the development of the theory of plate tectonics which validated but improved upon Wegener’s earlier theory of continental drift.

27. PLATE TECTONICS • This theory states that the Earth’s crust is broken up into several pieces called plates that move over a layer of hot magma (molten rock) in the mantle layer of the Earth, below the crustal plates.

28. Earth’s Plates

29. PLATES • This theory states that the earth’s crustal plates are made up of two things: • 1) Continental Crust which is much older and less dense and • 2) Oceanic Crust which is younger and more dense

30. Evidence to Support the Plate Tectonics Theory • 1.) Magnetic Anomalies– magnetic particles in rocks of the ocean floor align themselves with the magnetic poles. When the magnetic poles reverse themselves every 100 000 years, so do the magnetic characteristics in the rocks on the ocean floor. Ocean floor rocks show these magnetic anomalies in a matching pattern on either side of the Mid-Atlantic Ridge, supporting the idea that the sea floor is spreading in opposite directions from the Ridge.

31. Magnetic Anomalies Reverse Pattern Normal Pattern When the magnetic pole is in the Southern Hemisphere the rocks show a record of a reverse magnetic pattern. Mid-Atlantic Ridge

32. Evidence to Support the Plate Tectonics Theory • 2.) Plate Boundaries – scientists found that the global distribution of earthquakes and volcanic activity helped to locate the edges of tectonic plates. The Boundaries are found along the path of most volcanic and earthquake activity sites.

33. WHICH PLATE DO WE LIVE ON? • The North-American Plate!

34. CONVECTION CURRENTS • The Earth’s crustal plates move due to convection currents in the Asthenosphere layer of the upper mantle.

35. The Crust and Upper Mantle Heat from the core, causes magma in the upper mantle to move.

36. HOW CONVECTION WORKS As magma gets heated by the core it becomes less dense and begins to rise. As it rises away from its heat source, it then begins to cool down. The cooler magma becomes more dense than surrounding material and then sinks towards the core, where it gets re-heated. Hot magma rises again creating a continuous movement called a convection current or cycle of moving magma in the mantle.

37. CONVECTION CURRENTS

38. CONVEYOR BELT • The continental and oceanic crust act like a conveyor belt on top of this moving magma. Convection currents in the mantle move the crustal plates i) towards each other (converging and subducting), ii) away from each other (diverging) and iii) side by side (transforming) past each other.

39. PLATE MOVEMENT Mid-Atlantic Ridge ↓

40. CREATIVE FORCEWrite examples on handout of the diagrams of plate boundary movement • Tectonic plate movement can be creative in that it can create mountain ranges when plates collide such as the Himalayas that border India, Nepal and Pakistan and the Rocky Mountains in North America.

41. 1.a) PLATE CONVERGENCE (colliding plates create mountain ranges)

42. DESTRUCTIVE FORCE • Plate movement can also be considered destructive as plates that subduct (one plate dives below another) can consume crustal rock and turn it back into magma with heat and pressure.

43. 1.b) PLATE SUBDUCTION

44. What happens next? • When plates collide or subduct, they create erupting volcanic mountains, and deep ocean trenches (a very deep ditch on the ocean floor). Examples include the Andes Mountains on the West coast of South America and the Mariana Trench, east of The Philippines on the Pacific Ocean Floor.

45. OCEAN TRENCH

46. 2.) PLATE DIVERGENCE(plates separating) • When plates diverge or separate, they move away from each other causing the crust in between to stretch and become thin and brittle. This make it easy for magma to rise up and create mid-ocean ridges or rift valleys.

47. OCEAN RIDGES(The Mid-Atlantic Ridge)

48. 3.) TRANSFORM PLATES • Where plates slide past one another there are transform plate boundaries. As the plates are jagged they get stuck and pressure builds up, eventually breaking apart in an earthquake.

49. TRANSFORM (SLIDING) PLATES

50. TRANSFORM BOUNDARY • There is a major transform plate boundary in California where the San Andreas Fault is located, along which Earthquakes are common.