Lesson 2 Worksheet Seafloor Spreading

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Lesson 2 WorksheetSeafloor Spreading
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What is seafloor spreading?

• 1. What forms basalt?
• Lava that cools and solidifies
• 2. Which type of rock forms oceanic crust?
• Basalt
• 3. What happens to old oceanic crust as new
  oceanic crust forms?
• New crust pushes old crust away from the ridge

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• 4. What happens to the density of rock as it
  cools
• It becomes more dense
• 5. Where does the crust move as it becomes
  denser?
• Away from the mid-ocean ridge
• 6. Which force draws the cooler, denser crust
  downward and away from the ridge?
• Gravity

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• 7. What is formed when lava cools and
  crystallizes on top of the oceanic crust?
• Basalt (sediment)
• 8. Where is seafloor sediment thickest?
• Far away from mid-ocean ridge
• 9. What shape does the seafloor take where
  sediment is the thickest?
• Smooth plain
• 10. What is this area of the seafloor called?
• Abyssal plain

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• 11. What is the ocean crust always doing?
• Spreading
• 12. What happens as the ocean crust spreads?
• Continents move!

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• 13. What does the crust record as it cools?
• Direction of Earths magnetic field
• 14. What does basalt contain that makes this
  possible?
• Iron-rich minerals
• 15. What forms when Earths magnetic field
  changes direction?
• Magnetic stripes on ocean floor
• 16. What do magnetic stripes confirm?
• Ocean crust is made at mid-ocean ridge and is
  carried away from ridges as magma flows upward
  and out as lava

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What evidence is used to support seafloor
spreading?

• What does normal polarity mean?
• It means that magnets point north.
• 2. What does reversed polarity mean?
• Changes direction and magnets point south
• 3. How can scientists tell when changes occur in
  Earths magnetic field?
• Minerals give a magnetic signature that will
  point either north or south.

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• 4. How often do magnetic reversals occur?
• Every few hundred thousand (100,000) years to a
  few million (1,000,000) years
• 5. What do Earths magnetic stripes indicate
  about ocean crust?
• New ocean crust is found at mid-ocean ridges and
  older crust is further away.
• 6. How do Earths magnetic signatures support the
  idea that continents move?
• It shows that crust is moving and the seafloor is
  spreading.