1. Plate Tectonics
KWL
then
Birth of a theory

2. The Earth’s surface is made up of moving, solid pieces called plates (Reference Tables). Some of these plates are moving together and some are moving apart. Plate tectonics is the study of the formation and movement of these plates.

4. Oceanic crust is denser than continental crust.
The Earth’s plates are part of the lithosphere. The lithosphere considered to be the crust and the upper part of the mantle.
The oceanic crust is mainly made of the igneous rock basalt, while the continental crust is made of the igneous rock granite.
Oceanic crust is denser than continental crust.

5. The lower part of the mantle is called the asthenosphere
The lower part of the mantle is called the asthenosphere. This layer has similar composition to the upper mantle, but it is partially melted. This makes the asthenosphere like a very thick “liquid”

6. The “liquid” property of the asthenosphere allows it to flow very slowly.
You can think of the lithospheric plates as “floating” on the asthenosphere.

7. The heat from inside the Earth causes convection currents to form in the asthenosphere.
Where the convection currents rise, new material (molten rock) forces the plates apart.
Where the convection currents are sinking, the plates are moving together.

8. Convection Cells

9. So, what causes plates to move?
Convection currents: drag and move the lithospheric plates above the asthenosphere
(three sources of heat produce the convection currents):
Leftover heat from earth’s formation
Decay of Radioactive elements
Plate friction

10. Convection Currents in the mantle drag and pull the lithospheric plates above them

11. ARROWS IN THE ASTHENOSPHERE SHOW PLATE MOVEMENT DUE TO CONVECTION

12. The arrows shown in the asthenosphere represent the
inferred slow circulation of the plastic mantle by a process
called
(1) insolation (3) conduction
(2) convection (4) radiation

13. II. Evidence of Plate Movement: Continental Drift

14.
The shape of the west coast of Africa and the east coast of South America seem to fit together like a puzzle. It is believed that they were once together, but moved apart over time (Continental Drift).

15. Evidence for plate tectonics and continental drift
Pieces fit together like a jig-saw puzzle.
Particularly South America and Africa

16. Wegener used documented cases of fossil organisms (land animals) that had been found on different continents that could not have crossed the current oceans.

17. 2. Similar fossil remains in Africa and South America of a reptile that is found nowhere else in the world.

18. Matching Mountain Ranges
3. Distinctive rocks were also found in Africa and South America in regions where the two continents were most likely joined together.

19. 4. The majority of earthquakes and volcanoes are found in belts that occur along plate boundaries (where the plates are moving). Ex. the Pacific Ring of Fire.

20. A new hope: Sea-Floor Spreading
MID-ATLANTIC RIDGE
50,000 km. Long mountain range on the ocean floor

21. BrainPop- Plate Tectonics

23. Evidence for Plate Tectonics
During WWII, the U.S. in an effort to find any advantage that would help out submarines in the war effort, scientists found that the iron in the rock at the mid-ocean ridge sometimes pointed North and sometimes pointed South
Lava is a mixture of melted minerals of which Iron is a very common one. Iron is attracted to the Earth’s magnetic North Pole and prefers to line up with Earth’s magnetic field. While lava is liquid, the bits of iron will tend to line up with a magnetic orientation pointing at the North Pole. When the lava solidifies, the magnetic orientation is frozen into the rock- essentially; it will have a “north end” and a “south end.”
Back in World War II, the United States, in an effort to find any advantage that would help out submarines in the war effort, collected any type of data possible about the ocean and ocean floor. When they dragged a magnetic detector along the ocean floor, they discovered that the rocks making up the ocean bottom either had a magnetic orientation pointing to the North Pole or to the South Pole. As the magnetic detectors were dragged along the ocean floor, the orientation of the rock flipped from North to South- but never any other direction. They discovered a very quirky behavior of our planet: for some still-unexplained reason, at random times in Earth’s past, the magnetic orientation of the planet reversed- several times. In other words, if you traveled back in time with a compass, sometimes it will point north and other times it will point South.
The significance of these two points becomes clear when we have a map of the magnetic orientation of the entire Atlantic Ocean floor. Imagine that the North-oriented rocks (usually referred to as “normal polarity”) are colored white while the South-oriented (“reversed polarity”) rocks are colored black. What we will see is a striped pattern which runs parallel to the coasts of the Atlantic shores. In addition, the magnetic stripe pattern that emerges as we cross the Atlantic floor from the USA to the Mid-Atlantic Ridge is an exact mirror-image of the pattern from the Mid-Atlantic Ridge to Europe. This implies that the ocean floor is splitting at the Mid-Atlantic Ridge, new rock is being made at the ridge, and the new rock (along with its magnetic orientation) is split and each half is carried away from the ridge as the ocean floor spreads.

24. How could this be?
Basalt is iron rich and contains magnetite. Magnetite acts like a little magnet and aligns itself with the orientation of earth’s magnetic field.
When magma solidifies, the alignment is “locked in” recording Earth’s magnetic orientation at the time of cooling.

25. MAGNETIC STRIPE EVIDENCE
North Oriented Rocks are said to have NORMAL POLARITY
South Oriented Rocks are said to have REVERSED POLARITY

26. The earth’s magnetic field has reversed hundreds of times

29. POLARITY FLIPPING
AGE INCREASES AWAY FROM OPENING - RIDGE

30. Older
Older
Youngest

31. 5. Magnetic polarity reversals are recorded in rocks on the ocean floor as the sea floor spreads apart. During certain periods in Earth’s history, the magnetic fields have reversed (a compass would point south during a reversal). Minerals containing iron found in the igneous rocks on the ocean floor would shift before the magma cooled and hardened.

32. If the polarity changed, the new magma would cool with the minerals shifted in the opposite direction. This change is recorded in the rocks.

34. Which graph best represents the geologic age of the surface bedrock on the ocean bottom?

35. 6. Heat flowing out of the rocks is greatest where the rocks are spreading apart (rising convection current), and decrease as you move away from the center (sinking convection currents).
HOT! HOT! HOT!

36. Glacier Evidence Not in notes Woohoo Animations!!!!!

37. Plate Tectonics
An Introduction WS

38. “Uh-Oh!”: Problems with Continental Drift….

39. …an alternate explanation?
1928: Arthur Holmes suggested magma rises toward the crust, spread, and sinks again. (Convection current)
1930: Wegner dies, unable to adapt Holmes’ idea to his theory.

40. Mantle/Crust Structure

41. Evidence for Plate Tectonics
 Ocean Drilling
The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted.
The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.

42. Standard Deviants – Plate Tectonics

43. Sea-Floor Spreading is a Divergent Plate Boundary
Creates New Crust

44. III. Kinds of Plate Boundaries
Diverging Boundaries- this is where the plates are moving apart at spreading centers (on the ocean floor). These boundaries form mid-ocean ridges or rises (like underwater mountain ranges). Between the peaks of the ridge are valleys called rift valleys. Ex. mid-Atlantic Ridge

45. SPLITS APART CONTINENTS TO CREATE NEW OCEANS

46. Spreading Center

47. New Ocean forming – linear Red Sea
When it grows up, it will be like the Atlantic Ocean

48. EAST AFRICAN RIFT VALLEY – CONTINENTAL RIFT

49. In Afar, Ethiopia, a 40-mile magmatic rift that opened up 1 year ago

50. B. Sliding Boundaries!!!
As the name implies, this is where two plates are sliding past each other. The sliding movement often causes earthquakes to occur. This happens along faults. A fault is nothing more than a crack in the Earth’s crust where movement has occurred.
Ex. North American Plate and the Pacific Plate are sliding past each other along the San Andreas Fault in California

51. TRANSFORM PLATE BOUNDARIES
Transform Fault Boundaries
TRANSFORM PLATE BOUNDARIES
At a transform fault boundary, plates grind past each other without creating or destroying the lithosphere.
SHALLOW EARTHQUAKES
 Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they roughly parallel the direction of plate movement.

52. Boundaries: Transform

53. SAN ANDREAS TRANSFORM FAULT

54. Transform Fault Boundary AT MID-OCEAN RIDGES

55. CONVERGENT BOUNDARIES – DESTROYS CRUST
If new crust is created at divergent boundaries, is earth getting larger?
CONVERGENT BOUNDARIES – DESTROYS CRUST
Oceanic Crust converging with Continental Crust
Oceanic crust converging with Oceanic Crust
Continental Crust converging with Continental Crust

56. C. Converging Boundaries- this is where two plates are coming together.

57. Collision boundary- this is when the two plates that are moving together are both continental plates. The collision causes the plates to form a single, larger continent and the crust is pushed upward into a mountain range. Ex. Himalayan Mountains (including Mt. Everest). The Indian Plate and the Eurasian Plate are still moving together, so Mt. Everest is still slowly getting taller!!

58. Continental Crust – Continental Crust Convergent Boundary NO SUBDUCTION - COLLISION ZONE
WHY YOU FIND MARINE FOSSILS ON TOPS OF MOUNTAINS

59. b. Subduction boundary - this is when one of the plates plunges under (subducts) the other plate. This occurs between two oceanic plates, or an oceanic and continental plate. The most common characteristic of a subduction boundary is the formation of a deep-sea trench. These trenches are the deepest locations in the ocean

60. OCEAN CRUST - CONTINENTAL CRUST SUBDUCTION – TRENCH FORMS

61. Oceanic-Continental Convergent Boundary - SUBDUCTION
DENSER OCEANIC CRUST GOES DOWN INTO MANTLE

62. OCEAN CRUST –OCEAN CRUST CONVERGENCE - SUBDUCTION

63. *Because oceanic crust is denser than continental crust, the oceanic crust will always subduct underneath the continent.
**Volcanoes always seem to form at subduction boundaries. If two oceanic plates converge, volcanic islands will form. If one of the plates is continental and the other oceanic, the volcanoes will form along the edge of the continent.

64. Oceanic Crust – Oceanic Crust
Older, denser oceanic crust is SUBDUCTED (sinks below)
VOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS
TRENCH FORMS

65. STARTS OUT AS OCEAN-CONTINENT CONVERGENCE AND THEN AS OCEAN CRUST IS SUBDUCTED TURNS INTO CONTINENT TO CONTINENT
WHY YOU FIND MARINE FOSSILS ON TOPS OF MOUNTAINS

66. Collision of India and Asia

67. More Evidence for Plate Tectonics
Boundary Animations

68. Convergent plate (subduction) boundaries have deeper earthquakes Divergent plate boundaries and Convergent Continent-Continent collision zones have shallow earthquakes

69. Convergent
Indian-Australian Plate and the Pacific Plate (oceanic crust to oceanic crust) are converging forming the Tonga Trench.
f07_58_pg196
Deep EQ’s
f07_58_pg196.jpg
f07_58_pg196

70. The greatest number of earthquakes in the cross section occurred at:
Sea level
Between sea level and a depth of l00 kms.
3. at a depth between 100 – 300 kms.
4. At a depth between 300 – 600 kms.

71. Which cross section has arrows that best represent the relative motion of the crustal plates along the Wadati-Benioff zone beneath the Tonga Trench?

72. SUMMARY 3 PLATE BOUNDARIES
DIVERGING
CONVERGING (SUBDUCTION ZONE)
Oceanic Crust – Continental Crust
Oceanic Crust - Oceanic Crust
CONVERGING (COLLISION ZONE)
Continental Crust – Continental Crust
TRANSFORM

75. 3 types of plate boundaries caused by convection currents
CASCADES
MID-ATLANTIC RIDGE
TRENCH

76. Mid-ocean ridges (rifts) normally form where tectonic plates are
(1) converging (3) stationary
(2) diverging (4) sliding past each other
The motion of the convection currents in the mantle beneath the Atlantic Ocean appears to be mainly making this ocean basin
(1) deeper (3) wider
(2) shallower (4) narrower

77. More Evidence for Plate Tectonics
 Hot Spots
A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands.
Hot spot evidence supports that the plates move over the Earth’s surface.

78. HOT SPOTS
Major regions of volcanic activity in the interior of plates away from plate boundaries.
The cause of these hot spots is thought to be plumes of magma rising up from mantle producing sites of active volcanism.
As the plate moves over a hot spot, a chain of volcanic mountains forms, like Hawaiian Islands

79. Hot Spot

81. This diagram provides evidence that the Pacific Tectonic
Plate is moving toward the
(1) south (3) southwest
(2) east (4) northwest