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Understanding Crustal Movement: The Egg Model of Earth's Layers

This chapter explores the concept of crustal movement through the "Egg Model" of the Earth, illustrating its various layers: the thin crust, the Moho layer, the outer core, and the inner core. It explains different types of crust (oceanic and continental) with their distinct densities and compositions, discussing plate boundaries such as convergent, divergent, and transform, and their geological impacts. Key topics include the cause of plate movements from convection in the mantle, theories of crustal dynamics, and real-world examples like the San Andreas Fault and the formation of the Hawaiian Islands.

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Understanding Crustal Movement: The Egg Model of Earth's Layers

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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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