Plate Tectonics

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Plate Tectonics

• Section 1 Earths Interior
• Section 2 Convection and the Mantle
• Section 3 Drifting Continents
• Section 4 Sea-Floor Spreading
• Section 5 The Theory of Plate Tectonics

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Earths Interior

• How have geologists learned about Earths inner
  structure?
• Geologists have used two main types of evidence
  to learn about Earths interior
• Direct evidence
• from rock samples
• Indirect evidence
• from seismic waves

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Earths Interior

• Geologists cannot look inside Earth
• Use an indirect method.
• Seismic Waves (Earthquake waves)
• Study how they travel through Earth.
• Data reveals several layers

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Earths Interior
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Earths Interior

• Crust
• Mantle
• Outer Core
• Inner Core

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Earths Interior

• Crust
• Solid layer of rock that includes both dry land
  and the ocean floor
• Between 5 and 40 km thick
• Dry land
• Granite
• light in color
• less dense
• Ocean floor
• Basalt
• dark in color
• more dense

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Earths Interior

• Mantle
• very hot, but solid rock
• about 3,000 km thick
• Lithosphere
• Crust and Upper Mantle region
• Lithos, Greek for Stone
• Asthenosphere
• Remainder of Mantle
• Very soft and hotter than Lithosphere
• Asthenes, Greek for Weak
• Lower Mantle
• Solid and extends to the Core region

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Earths Interior
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Earths Interior

• Core
• Mostly Iron and Nickel
• Outer Core
• molten metal (Fe and Ni) that surrounds the Inner
  Core.
• Liquid
• creates the magnetic field of the Earth
• Bar-magnet with North and South Poles
• Inner Core
• dense ball of metal (Fe and Ni)
• Intense pressure prevents it from changing from
  solid to liquid.

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Earths Interior

• Pressure and Temperature increase as you move
  towards the center of the Earth

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Earths Interior

• Core

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Earths Interior Assessment Questions

• Why is it difficult to determine Earths inner
  structure?
• How are seismic waves used to provide evidence
  about Earths interior?
• List Earths three main layers
• What is the difference between the lithosphere
  and the asthenosphere?
• In which layer is each located?

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Section 1.2 Convection in the Mantle

• How is heat transferred?
• There are three types of heat transfer
• Radiation
• Conduction
• Convection

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Radiation

• The transfer of energy through space.
• No direct contact between a heat source and an
  object.
• Sunlight warms the Earth

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Conduction

• Heat transfer within a material or between
  materials that are touching.
• Holding a hot spoon.
• Conduction is responsible for some of the heat
  transfer inside Earth.

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Convection

• Heat transferred by the movements of liquids and
  gases.
• Caused by
• Density differences
• Gravity
• Density
• mass in a given volume
• More heat expansion less dense
• Less heat contraction more dense

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Convection

• What causes convection currents?
• Gravity
• Difference in Density of liquids or gases.
• Gravity pulls denser materials downward
• More heat expansion less dense moves upward
• Less heat contraction more dense moves
  downward

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Convection
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Convection Currents

• What causes convection currents in Earths
  mantle?
• Heat from the core and mantle causes convection
  currents in the mantle.

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Visual Summary of the Three Types of Heat Transfer
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1.2 Assessment Questions

• 1. How is heat transferred?
• 2. What causes convection currents?
• 3. What causes convection currents in Earths
  mantle?
• 4. What is conduction?

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1.2 Assessment Questions

• 5. What is the role of gravity in creating
  convection currents?
• 6. What part of Earths interior is like the soup
  in the pot? What part is like the burner on the
  stove? (Fig 9)
• 7. How is heat transferred through space?
• 8. What is a convection current?

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1.2 Assessment Questions

• 9. In general, what happens to the density of a
  fluid as it becomes hotter?
• 10. Describe how convection currents form.
• 11. Name two layers of Earth in which
  convection currents take place.
• 12. What causes convection currents in the
  mantle?
• 13. What will happen to the convection currents
  in the mantle if Earths interior eventually
  cools down? Explain.

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Section 1.3Drifting Continents

• What was Alfred Wegeners hypothesis about the
  continents?
• What evidence supported Wegeners hypothesis?
• Why was Wegeners hypothesis rejected by most
  scientists of his day?

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Continental Drift

• Why do the coasts of several continents match so
  neatly?
• West Africa and Eastern South America seem to fit
  together like puzzle pieces.

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Continental Drift

• Alfred Wegener
• Hypothesized that Earths continents has moved
  over time.
• All part of one large, ancient landmass
• Drifted apart over time
• His idea was called Continental Drift

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Pangaea

• Ancient landmass
• All Lands
• All continents connected together
• 300 million years ago

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Pangaea

• Slowly broke apart to where continents are
  located today.
• Supported by studying
• land features
• fossils
• evidence of climate change

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Pangaea

• Supporting Evidence
• Land Features
• mountain ranges on Africa and South America
  lined-up.
• coal fields in Europe and North America match-up

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Supporting Pangaea Land Features
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Pangaea

• Supporting Evidence
• Fossils
• Glossopteris
• fernlike plant
• Mesosaurus and Lystrosaurus
• land-dwelling dinosaurs
• Fossils of these organisms are found on many
  different continents separated by great oceans!!
• How could that be possible?

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Supporting Pangaea Fossils
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Pangaea

• Climate
• Spitsbergen
• Present location Arctic Ocean (Cold!!)
• Tropical plant fossils are found there!
• South Africa
• Present climate Mild/Warm
• Deep scratches, caused by glaciers are found in
  the crust.
• Glaciers exist in very cold environments!!
• Climates changed because landmasses moved.

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Hypothesis Rejected!!

• Wegener was not able to provide a satisfactory
  explanation for the force that pushes or pulls
  the continents.
• More evidence would be needed.

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Mountain Formation

• Wegener hypothesized that when continents
  collide, their edges crumple and fold.
• Huge mountains form.

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1.3 Assessment Questions

• 1. What was Alfred Wegeners hypothesis about the
  continents?
• 2. What evidence supported Wegeners hypothesis?
• 3. Why was Wegeners hypothesis rejected by most
  scientists of his day?

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1.3 Assessment Questions

• 4. What do the matching mountain ranges in Africa
  and South America show, according to Wegeners
  hypothesis?
• 5. How would continental drift affect the
  continents climate?
• 6. According to Wegener, how do mountains form?

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1.3 Assessment Questions

• 7. Who proposed the concept of continental drift?
• 8. According to the hypothesis of continental
  drift, how would a world map have changed over
  the last 250 million years?
• 9. What evidence supported the hypothesis of
  continental drift?
• 10. How did fossils provide evidence for
  continental drift?

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1.3 Assessment Questions

• 11. Deposits of coal have been found beneath the
  ice of Antarctica. But coal only forms in warm
  swamps. Use Wegeners hypothesis to explain how
  coal could be found so near to the South Pole.
• 12. Why did most scientists reject Wegeners
  hypothesis of continental drift?
• 13. Do you think the scientists of Wegeners time
  should have accepted his hypothesis? Why or why
  not?

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Chapter 1.4 Sea-Floor Spreading

• Mid-Ocean Ridges
• an undersea maintain chain where new ocean floor
  is produced.
• divergent (moving apart) plate boundary

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Chapter 1.4 Sea-Floor Spreading

• What device is used to map the ocean floor?
• Mapped in the mid-1900s by using SONAR.
• Underwater soundwaves
• How long does the echo take to travel? distance
  to the bottom.

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Mid-Ocean Ridge
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Chapter 1.4 Sea-Floor Spreading

• What is the process of Sea-Floor Spreading?
• Sea floor spreads apart along both sides of a
  mid-ocean ridge as new crust is added from below.

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Evidence of Sea-Floor Spreading

• What is the evidence of Sea-Floor Spreading?
• 1. Molten Material
• Bubble-shaped rocks found on the ocean floor.
• caused only by cooling magma

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Evidence of Sea-Floor Spreading

• 2. Magnetic Stripes
• Iron in molten rock aligns to magnetic poles
• Poles Flip over many thousands of years
• Repeated pattern of north and south orientation.
• pattern is the same on both sides of the
  Mid-Ocean Ridge.

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Magnetic Reversal Stripes
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Evidence of Sea-Floor Spreading

• 3. Drilling Samples
• Oldest rocks
• farther from Mid-Ocean Ridge
• Youngest rocks
• closer to Mid-Ocean Ridge

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Subduction at Trenches

• What happens at Deep-Ocean Trenches?
• Trenches
• Opposite of Sea-Floor Spreading
• Oceanic rock is forced downward, or subducts, and
  eventually melts into magma.

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Deep Ocean Trenches
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Subduction at Trenches

• Together, Subduction and Sea-Floor Spreading act
  as a conveyor belt
• cooling magma into new rock (Mid-Ocean Ridges).
• melting old rock into magma (Trenches)

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1.4 Assessment Questions

• 1.Along what feature of the ocean floordoes
  sea-floor spreading begin?
• 2.What are the steps in the process of sea-floor
  spreading?
• 3.What three types of evidence provided support
  for the theory of sea-floor spreading?
• 4.How do rocks along the central valley of the
  mid-ocean ridge provide evidence of sea-floor
  spreading?

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1.4 Assessment Questions

• 5.Where would you expect to find the oldest rock
  on the ocean floor?
• 6.What is a deep-ocean trench?
• 7.What happens to oceanic crust at a deepocean
  trench?