Plate tectonics

1. Plate tectonics

2. The Earth is divided into layers by density. As the Earth solidified during the formation of the solar system elements with higher density were drawn toward the center of the Earth by gravity.

3. Oceanic crust is comprised mainly of the rock basalt Earth’s Crust

4. Continental crust makes up the land masses. This thicker, less dense material allows the continents to rise above sea level and remain dry for very long periods Continental crust is made primarily of the rock granite Earth’s Crust

5. As the very hot core heats the material in the Mantle it causes the material to move in a circular pattern. The mantle material heats up and rises and then cools and sinks. This circular pattern of movement within the mantle (called a convection current) pushes the lithospheric plates as they float. The movement and interaction of these plates causes most of the large scale changes on Earth's surface.

7. Alfred Wegener a German scientist was the first to propose this theory to the scientific community in the early 1900’s Continental Drift

8. Pangea was the name for this supercontinent that began to break up about 200 million years ago Continental Drift

9. Wegener’s theories were not accepted at the time because his explanations were not supported by physicists Continental Drift

10. His explanation for movement was that the continents plowed through the seafloor crust like moving islands Continental Drift

11. His explanation for the reason why the continents moved was the spinning of the earth Continental Drift

12. Although his explanations for the reason the continents drifted were incorrect there was still convincing evidence that they were indeed once together. Evidence of Continental Drift

13. Rock formations in the Appalachian Mountains matched up with ones in Greenland. Evidence of Continental Drift

14. Fossil evidence found in South America and Africa were especially strong Evidence of Continental Drift

15. Bones from the Mesosaurus and Kannemeyerid were found in the same rock formations in Brazil and Chad Evidence of Continental Drift

16. Even glacial striations from ancient Ice ages were found to match perfectly Evidence of Continental Drift

17. Climatic evidence found that there were coal deposits in Antarctica suggesting that continent was at one time much closer to the equator Evidence of Continental Drift

18. In the early 1960’s new evidence revealed the process on how the continents could indeed move Sea Floor Spreading

19. Advances in sonar technology in the 1940’s and 50’s allowed us to begin to accurately map the seafloor Sea Floor Spreading

20. This evidence proved that the seafloor was not flat and featureless as once thought. Vast underwater mountain chains and deep trenches were discovered. Sea Floor Spreading

21. Earthquakes and volcanic activity was prevalent in certain parts and missing in others Sea Floor Spreading

22. The ocean floor was found to be much younger than the continental crust Sea Floor Spreading

23. The thickness of the layers of sediments increased with the distance on either side of the ocean ridges Sea Floor Spreading

24. Once scientists were able to bring sea floor samples to the surface they were able to determine that a record of the seafloor was being kept by Earth’s magnetic field Paleomagnetism

25. Paleomagnetism is the study of this magnetic record using data gathered from iron-bearing minerals Paleomagnetism

26. The magnetic records for the seafloor on either side of the mid-ocean ridges matched perfectly showing that the seafloor was growing outward from the ridges in both directions Paleomagnetism

27. Theory of Plate Tectonics states that the Earth’s crust and rigid upper mantle are broken into enormous slabs called plates. The Theory of Plate Tectonics

28. There are 17 known plates The Theory of Plate Tectonics

29. The plates do not remain still. They slide across the partially molten mantle material of the asthenosphereas a result of convection currents deep in the Earth’s interior. The Theory of Plate Tectonics

30. Tectonic plates interact at places called plate boundaries. Plate Boundaries

31. Typically, since the Earth is spherical the plate boundaries would appear as the threads of a baseball weaving through the mid-ocean rifts and around the smaller plates. Plate Boundaries

32. Notice that ALL of the major plates include both continental and oceanic crust Plate Boundaries

33. Some plates move towards each other, some move away, and some slide horizontally past each other. Each interaction results in geologic process and characteristics that we can now associate with it. Plate Motions

34. Divergent boundaries are places where tectonic plates are moving apart Plate Motions

35. Most divergent boundaries are found on the seafloor where they form mid-ocean ridges Plate Motions

36. Iceland is a continuation of the Atlantic mid-ocean ridge Plate Motions

37. The Arabian Peninsula is an example of a newly formed divergent boundary as it separates from the rest of Africa Plate Motions

38. Convergent boundaries are where plates move toward each other. These boundaries give us the most interesting geologic features. There are three types of convergent boundaries Plate Motions

39. Oceanic crust to oceanic crust results in the subduction of one of the two plates and an island arc Plate Motions

40. Subduction is the process of one plate descending beneath the other Plate Motions

41. The Phillippines are a noticeable example Plate Motions

42. Oceanic to continental convergence also results in the subduction of the oceanic crust Plate Motions

43. A volcanic mountain range such as the western portions of North and South America is the result Plate Motions

44. The oceanic crust always subducts because it is denser than continental crust Plate Motions

45. Continental to continental convergence results in folded mountains Plate Motions

46. The Himilayas are an active folded mountain chain Plate Motions

47. Transform boundaries occur where plates slide horizontally past each other. They rarely are seen on the continents however the San Andreas Fault in California is an exception Plate Motions

48. Most earthquakes occur when rocks fracture deep within the Earth Earthquakes

49. Compression decreases the volume of a material Earthquakes

50. Tension pulls the material apart Earthquakes