Do now:

1
Do now

• Read 4.2

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Module F 4.2 Seafloor Spreading

• Objectives
• You will learn to explain seafloor spreading.
• You will learn to recognize how age and magnetic
  clues support the theory of seafloor spreading.

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Clues on the Ocean Floor

• - invention of ____________________ allowed the
  construction of accurate maps of the ______ floor
• - using sound waves, researchers discovered an
  ___________ system of _______, or __________, and
  valleys like those found on the ____________

echo-sounding devices
ocean
underwater
ridges
mountains
continents
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Seafloor Spreading!!!
Harry Hess

• - Early 1960s __________ proposed this theory
• - the idea that _______ from Earths _______
  rises to the surface at mid-ocean ridges and
  cools to form new ________, which new magma
  slowly pushes away from the ridge

magma
mantle
seafloor
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Evidence for Seafloor Spreading!!!

• 1. Age Evidence

__________________ ____________
2. Magnetic Clues
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1. Age Evidence

• - there were no rocks older than
• ___________ years, however, some ___________
  rocks are almost
• _________ years old
• - youngest rocks were at
• _________________
• - age of rocks became ______ farther from the
  ridges on both sides

180 million
continental
4 billion
mid-ocean ridges
older
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2. Magnetic Clues

• - magnetic data is recorded by a ______________
• - rocks on the ______ floor showed magnetic
  reversals
• - the magnetic alignment of the rocks reverses
  back and forth in strips ________ to the
  mid-ocean ______

magnetometer
ocean
parallel
ridge
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LETS REVIEW!

• The invention of _____________ allowed the
  construction of accurate maps of the ocean floor.
• What are mid-ocean ridges?
• Who discovered the idea of seafloor spreading?
• What is a trench? When is one formed?
• What two pieces of evidence proved the theory of
  seafloor spreading to be correct?

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Homework!!!

• Read section 4.2 and do questions 1-5 Due
  Wednesday
• Notes Packet due Thursday
• Study for 4.2 quiz Thursday