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Chapter 4-1

Chapter 4-1. Crustal Movement. The EGG Model of the Earth. Shell = Crust Very thin compared to entire egg Slimy Skin = Moho Keeps the white from leaking out White = Outer Core Soft & mushy, but still a solid Yolk = Inner Core Denser *Needs to be divided into 2 layers.

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Chapter 4-1

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  1. Chapter 4-1 Crustal Movement

  2. The EGG Model of the Earth • Shell = Crust • Very thin compared to entire egg • Slimy Skin = Moho • Keeps the white from leaking out • White = Outer Core • Soft & mushy, but still a solid • Yolk = Inner Core • Denser *Needs to be divided into 2 layers

  3. Layers of the Earth

  4. Layers of the Earth • Think about the ‘Egg” model • Always start at the stick person to find the location in the Earth, before you look for data • Be careful when reading the graphs • All rocks are found in the GREEN layer • Different crusts have different densities

  5. Crust Oceanic Continental Low-density rocks (like granite) Rich in Aluminum (Felsic) Average thickness is 20-40 km Collisions cause sediments at rivers to uplift (creating met. & possibly igneous rocks in the process) • High-density rocks (like basalt) • Rich in Iron & Magnesium (Mafic) • Average thickness is 10 km • NOT thinner or denser because of the ocean on it – because of the rock properties

  6. Crustal Boundaries • Located along the edge of the plates • Interaction depends on plate movement • Land formations are the result of the crustal movement • There are 3 types • Convergent • Divergent • Transform

  7. Convergent Boundaries • Plates are moving towards each other • Resulting landforms depend on plate types due to density differences • Same Type of Plates (Cont & Cont) • Neither plate will give in • Mountains will form

  8. Convergent Boundaries • Different type of plates (Cont & Oceanic) • The denser one (Oceanic) will go under the less dense one (subduction) & melt into magma • Intersection will form a deep trench under water • As this plate moves, earthquakes will occur along the interface between the plates • The less dense one (Cont) will get bent due to the collision & form mountains (possibly volcanoes if magma gets through)

  9. Divergent Boundaries • Plates are moving away from each other causing a rift valley to form • This valley will then fill with magma/lava & form new crust • This new crust is still very warm, so it will be elevated & form a mountain chain • As the crust cools, it will contract • Most of these boundaries are under water

  10. Divergent Boundary ABOVE Water

  11. Transform Boundaries • Plates are rubbing against each other, cause lots of earthquakes • There is little or no lava involved • Having many frequent small earthquakes is better • otherwise there will be less, but they will be stronger & cause more damage • the end result will still be the same amount of movement • San Andreas Fault (California)

  12. San Andreas Fault Pacific Plate North American Plate http://www.youtube.com/watch?v=ZxPTLmg0ZCw

  13. Cause of Plate Movement • Convection of the Magma in the Plastic Mantle • Look at the arrows on page 10 of the ESRT http://www.youtube.com/watch?feature=endscreen&NR=1&v=ryrXAGY1dmE

  14. Pattern of Boundaries • Most Earthquakes & Volcanoes are concentrated in narrow belts • These belts help indicate where plate boundaries occur • See ESRT page 5

  15. Theories of Crustal Movement • 1910 • Professor Al Wegener • Continental Drift Theory • Pieces fit like a puzzle • Rocks match (NJ & Africa) • Fossils match • Fossil Fuel Deposits (PA. Alaska, & Antarctica) • Couldn’t explain HOW

  16. Sea-floor Spreading • 1960 • Harry Hess • Hypothesis that the sea floor forms out of the mid-ocean ridges • Moves away from the ridge like a conveyor belt due to the magma underneath (what Prof Al couldn’t explain) • Age of rocks are older as you move away from the ridge on both sides

  17. Reversed Polarity • If there is magnetic material in molten rock, it will be aligned by the magnetic field of the Earth • When it cools & hardens, a record of the Earth’s polarity at that time is preserved in the rock • Across the Atlantic ocean, there is a pattern

  18. Plate Tectonic Theory • Put together: • Continental Drift • Sea-floor Spreading • Convection of the plastic mantle • Reversed polarity • Some plates are all oceanic crust • Some plates have continental “chunks” on them • The plates are separating, colliding, or sliding past each other (plate boundaries) • The plates rest on the athenosphere (plastic mantle) which is moving in slow, powerful convection cells

  19. Just a Theory • There are still places that cannot be explained by these concepts… • 3 possible driving forces for plate movement are: • Plates are pushed from the rear • Convection of the magma drag the plates • Descending denser plates pull the plate as it sinks into the plastic mantle • Keep an open mind…like Professor Al

  20. Hot Spots • Hole in the Moho that the plate slides over • Creates an active volcano • Once the plate moves the volcano becomes extinct because it has lost its source of magma • The Hawaiian Island chain is a great example

  21. Strata • Horizontal layers of sedimentary rock • If the layers are NOT horizontal then they are evidence of crustal movement

  22. Deformed Strata • The most common deformed strata are: • Tilting • Folding • Faulting

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