Plate Tectonics - Chapter 5

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  • 1 billion dollar mission to drill into the mantle in the Pacific Ocean at a spreading zone where the crust is the thinnest. Will have to drill 6 km (3.7 miles) beneath the ocean floor. However, in order to reach those samples, the team of international scientists must first find a way to grind their way through ultra-hard rocks with 10 km-long (6.2 miles) drill pip
  • Continental crust formed when the earth was still cooling off and is very very old. Oceanic crust formed from quickly cooling lava and is young because it is constantly being renewed.
  • Pangaea existed 300 million years ago. Pangaea began to break up 225 mya. Rodinia is a supercontinent that existed before Pangaea.
  • The poles are cold because they get less direct sunlight. The equator is warm because it gets direct sunlight.
  • The “Age of Dinosaurs” is the Mesozoic Era, which is divided into three periods: the Triassic (245-208 million years ago), Jurassic (208-145 million years ago), and Cretaceous (145-66 million years ago). Dinosaurs became extinct 65 mya.
  • New supercontinent called Pangaea Ultima.
  • The mid ocean ridge winds around the earth like the seams of a baseball.
  • Pillow lava is evidence of volcanic eruptions
  • The last magnetic field reversal was 780,000 years ago. On average it reverses itself every 200,000 years.
  • Ask students: What plate do we live on?
  • San Francisco is on the North American Plate LA is on the Pacific Plate
  • Rift Valley can eventually become so thin, stretched, and low that ocean water can come in filling new ocean basins.
  • The Appalachians started forming 470 mya and are much older than the Himalayas.
  • Mt. Everest is located between Nepal and China
  • The diagram shows the movement in centimeters. Ask Students: Where is the fastest movement occurring? (18.3 cm/year Pacific and Nazca Plates) Where is the slowest movement occurring? (1.7 cm/year Antarctic and African Plates) Ask students what type of movement is occurring at each.
  • Not in student Notepacket.
  • Plate Tectonics - Chapter 5

    1. 1. Section 5-1 Earth’s Interior
    2. 2. Exploring Inside the EarthGeologists have used twomain types of evidence tolearn about Earth’sinterior:1. Evidence fromexamining rock samples2. Evidence from seismicwaves-earthquakes producedifferent types of seismicwaves. Some waves cantravel through solids andliquids others can onlytravel through solids.-Also, they travel atdifferent speeds as theymove through differentmaterials.
    3. 3. Temperature Inside the Earth The graph shows how temperatures change between Earth’s surface and the bottom of the mantle. Interpreting Data: How does temperature change with depth in Earth’s interior? It increases with depth.
    4. 4. Temperature Inside the Earth•In addition to temperature, pressurealso increases as you go deeper intothe earth, just like a swimming pool!
    5. 5. The Crust•The crust is a layer of solid rock thatincludes both dry land and the ocean floor.•Although continental crust is thicker, it isless dense.•Granite is the most common rock on thecontinental crust and basalt is the mostcommon rock on the ocean floor.
    6. 6. The Mantle• Earth’s mantle is made up of rock that is very hot, but mostly solid. Scientists divide the mantle into layers based on the physical characteristics of those layers.1. Lithosphere-upper mantle and crust. Very rigid and solid!2. Asthenosphere-beneath lithosphere, softest part of the mantle. It is mostly solid rock but is able to bend and move like taffy. It does have some areas though which are melted (molten).3. Lower Mantle- below asthenosphere. Intense pressure makes the rock very solid which extends all the way to the core.
    7. 7. The Core• When the earth was forming, heavy metals like iron and nickel sank towards the center, or core. It consists of two parts:1.Liquid outer core• The motions of the moving metals and electrical charges in the outer core are thought to contribute to the earth’s magnetic field. When you use a compass, the needle aligns with the magnetic field.2. Solid inner core• Intense pressure squeezes the metals into a solid.
    8. 8. Section 5-2Convection and the Mantle
    9. 9. Types of Heat Transfer•You hold an ice cube and your handgets cold. Is your hand losing heat orgaining cold?•Only heat moves-cold is just theabsence of heat!•There are three types of heat transfer:radiation, conduction, and convection.
    10. 10. Types of Heat Transfer1. Radiation is the transfer of energy through space or air outwards in all directions from its source.2. Ex. Sunlight or heat from a fire.
    11. 11. Types of Heat Transfer2. Conduction is the transfer ofenergy through touch or contact – likegetting burned on a hot stove.
    12. 12. Convection Currents•3. Convection-Heating and cooling of a fluidwhich causes changes in the fluid’s densityand sets convection currents in motion.•Ex. When you heat water, the water nearestthe stove warms, expands, and becomes lessdense so it moves upward. It then cools,compacts, and moves downward again.
    13. 13. Convection Currents in Earth•Heat from the core (and the mantle itself)causes convection currents in the mantle.•These convection currents ultimately causelandmasses to move (more on this later)•What other layer of the Earth has convectioncurrents?•The outer core.
    14. 14. b
    15. 15. Section 5-3 DriftingContinents
    16. 16. Continental Drift•In 1910, a German scientist namedAlfred Wegener presented hishypothesis called Continental Drift. Itsaid that all the continents were oncejoined together in a single landmasscalled Pangaea and have since movedthrough the ocean moving to theircurrent locations.
    17. 17. Evidence for Continental Drift1. Land Features- The shapesof the continents matched!
    18. 18. Evidence for Continental Drift2. Climate – As a continent moves toward theequator, it’s climate becomes warmer. As acontinent moves toward the poles, its climatebecomes colder. But the continent carries with itthe fossils and rocks that formed at its previouslocations.•Tropical plant fossils have been found on islandsin the arctic ocean!
    19. 19. Evidence for Continental Drift•Striations left behind by glaciers arefound in rocks in areas such as SouthAfrica and India that now have verywarm climates
    20. 20. Evidence for Continental Drift3. Fossils- Fossils of the Glossopteris plant arefound in Africa, South America, Australia, India andAntarctica. Mesosaurus fossils are found in bothAfrica and South America.•These places are now separated by oceans!
    21. 21. Evidence for Continental Drift
    22. 22. Evidence for Continental Drift• Despite all of the evidence, Wegenercould not provide a satisfactoryexplanation for the pushes/pulls ofcontinents so his theory was rejectedeven up until the 1960’s.
    23. 23. Section 5-4 Sea-Floor Spreading
    24. 24. Mid-Ocean Ridge•The earth’s longest mountain range isunderwater! It is called the mid-ocean ridgesystem that was discovered using sonar (soundnavigation and ranging) in the mid-1900’s.•Sonar bounces sound waves off the ocean floorand records the how long it takes for an echo todetermine distances.
    25. 25. Mid-Ocean Ridge•In the mid-ocean ridge system, is a deepcentral valley with mountain peaks on bothsides.•What happens at these ridges?
    26. 26. What Is Sea-Floor Spreading?•In the 1960’s Harry Hess and others studied themid-ocean ridge and proposed the theory of sea-floor spreading:********At the mid-ocean ridge, magma erupts fromthe mantle, cools, and older rock moves outward onboth sides, adding new oceanic crust to eachside.********
    27. 27. What Is Sea-Floor Spreading?•As a result, the ocean floorsmove like conveyor belts,carrying the continents alongwith them.
    28. 28. Evidence for Sea-Floor SpreadingSeveral types of evidence support the theory of sea-floor spreading:1. Pillow Lava-• When lava that erupts in the ocean hits cold water it cools quickly and forms characteristic pillow shapes. This “Pillow Lava” has been found at mid-ocean ridges.
    29. 29. Evidence for Sea-Floor Spreading2. Magnetic stripes in the rockof the ocean floor•When rock cools, any iron inthe rock becomes magnetizedin direction of earth’smagnetic field. The rock has“magnetic memory”.•For unknown reasons, theearth’s magnetic fieldperiodically reverses itself.
    30. 30. Evidence for Sea-Floor Spreading•According to sea-floor spreading, new rock is being addedin equal amounts to both sides of the mid-ocean ridge.•Therefore, it is expected that rock strips of equal size andmagnetism should be parallel to each other on both sides ofthe ridge.•Scientists have used sensitive instruments that show thatthe “magnetic memory” of the rocks does alternate and is inthe same pattern on both sides of the ridge.•Because is found to be true, this is strong evidence for sea-floor spreading.
    31. 31. http://www.windows.ucar.edu/tour/link=/earth/interior/seafloor_
    32. 32. Evidence for Sea-Floor Spreading3. Drilling core samples-rock isyounger near the mid-ocean ridge andgets progressively older moving awayfrom the ridge. Glomar Challenger
    33. 33. Subduction at Trenches•If ocean floor is constantly beingmade at mid-ocean ridges, is theEarth constantly getting bigger?
    34. 34. Subduction at Trenches•Not only are there mid-ocean ridges inthe ocean, there are deep canyons in theoceans called deep-ocean trenches.•The further the ocean floor moves fromthe ridges, the cooler and denser itbecomes.
    35. 35. Subduction at Trenches•In a process taking tens of millions of years, cold,dense ocean floor far away from mid-ocean ridgessinks back into the mantle through deep-oceantrenches. This process is known as subduction.
    36. 36. The Challenger Deep• The Challenger Deep is the deepest point in the oceans and is located at the Southern End of the Mariana Trench. It is in the Pacific and is 6.78 miles deep!!
    37. 37. Subduction at Trenches•In the Pacific ocean there aremore deep ocean trenchesthan there are mid-oceanridges.•In the Atlantic ocean thereare more mid-ocean ridgesthan there are deep oceantrenches.•What is happening to the sizeof the Pacific? The Atlantic?•The Pacific is shrinking andthe Atlantic ocean is growing!•Because of sea-floorspreading, the distancebetween Europe and NorthAmerica is increasing by a fewcentimeters per year.
    38. 38. Section 5-5 The Theory ofPlate Tectonics
    39. 39. Plates•The lithosphere (crust and upper mantle) is broken intosections called plates.•These plates fit together along cracks in thelithosphere.•Plates can contain continents, the ocean floor, or both.
    40. 40. Plates•The mid-ocean ridge is actually one of thesecracks, a boundary between two plates. It is wheretwo different plates are moving away from eachother.
    41. 41. How Plates Move•The theory of plate tectonics states that plates are in aslow, constant motion driven by convection currents inthe earth’s mantle.•Convection currents in the mantle cause some warmmagma to rise and erupt at the mid-ocean ridge.•Convection currents push and pull the tectonic platesas shown in the diagram.
    42. 42. Plate Boundaries•A plate boundary is where different platesmeet. At a plate boundary, plates can collide,pull apart, or grind past each other.
    43. 43. Transform Boundaries1. A transform boundary is a place wheretwo plates slip past each other, moving inopposite directions. This boundary or breakin the rock is called a fault.•Crust is neither created nor destroyed•Earthquakes occur frequently along theseboundaries.
    44. 44. Transform Boundaries•The San Andreas Fault isa transform boundary inCalifornia where the NorthAmerican Plate and thePacific plate are movingpast each other.•Scientists predict that in10 million years LA andSan Francisco will passeach other!•Right now, scientists aremore concerned aboutearthquakes that aretriggered by themovement.
    45. 45. Divergent Boundaries•The place where two plates move apart, ordiverge, is called a divergent boundary.•The mid-ocean ridge is a divergentboundary-each side of the ridge is actually adifferent plate.
    46. 46. Divergent Boundaries•If Divergent boundaries form on land,they stretch and thin the crust creatingrift valleys.•Ex. Iceland and the Great Rift Valley inAfrica.
    47. 47. Convergent Boundaries•The place where two plates come together, orconverge, is called a convergent boundary.Trenches, or subduction zones are convergentboundaries!•At a convergent boundary, what happensdepends on the density !•Oceanic crust (mainly basalt) is always moredense than continental crust (mainly granite).******Whatever plate is denser, sinksunderneath the other plate!
    48. 48. Convergent BoundariesThere are 3 types of collisions at convergent boundaries:1. Continental / Continental-• Same density• Neither plate really subducted!• Folded mountains form• Ex. India collided with Asia to form the Himalayas 60 mya and is still colliding today!• Ex. North America collided with Europe and Northern Africa during the formation of Pangaea to form the Appalachians.
    49. 49. Convergent Boundaries2. Oceanic / Continental-•Oceanic plate denser•Oceanic plate is subducted and melting createsVolcanoes/Volcanic Mountains on the land•Ex. Mt. Saint Helens
    50. 50. Convergent Boundaries3. Oceanic /Oceanic-•Whichever plate is denser issubducted and melts creatingvolcanoes which may build up intovolcanic islands or “island arcs”•Ex. The Philippines
    51. 51. So how did marine fossils end up embedded in rock at the top of Mount Everest?•As India moved closer to Asia,the ocean between them wassubducted and became smallerand smaller, eventually becomingvery narrow.•In that narrow strip of oceanwere marine organisms that livedand died. Their shells werefossilized in the rock on the oceanfloor.•Then, when India finally collidedwith Asia, some of the fossils gotdriven up with the rest of thecontinental crust and overmillions of years it was pushed up5 miles to the “top of the world.”
    52. 52. Rate of Plate Movement•Using GPS technology to repeatedly measuredistances between specific points, geologistscan very accurately determine the movement.between plates.
    53. 53. Big Picture•It has taken the continents about 225million years since the breakup of Pangaeato move to their present locations.
    54. 54. End ofChapter!

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