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12.1 Evidence for Continental Drift
• If you look closely at a world map. It looks likes S. America and
Africa can fit together.
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12.1 Evidence for Continental Drift
• Early maps of the world caused Alfred _________ to propose
the ____________________________.
 The continents looked as though they might fit together like puzzle pieces.
 The continental shelves actually fit together even better.
 The large mountain ranges and coast lines match up. Each continent has a
continental shelf
Continent
Continental shelf
Ocean floor
All continental shelves are approximately 200m deep.
See pages 506 - 509
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12.1 Evidence for Continental Drift
 The original, supercontinent was named _________ by
Wegener.
 Wegener also realized that other evidence also supported
his theory.
1. There were ___________________________ and
________ on different continents.
• Rocks in Newfoundland are the same type rock with
the same age as the rocks in Norway and Sweden
2. There were _________ _________, like Mesosaurs,
on different continents.
• Similar fossils found at similar depths in Africa and
South America. Plants and animals are only found
in very specific locations around the world.
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12.1 Evidence for Continental Drift
3. There was evidence of different climates (eg.
glaciers) on warm continents.
• Fossils of warm weather plants found in
Antarctica Glacial rock in S. America and
Africa.
• Ice ages show the retreat of large icebergs.
These icebergs leave behind deep valleys
and scratches in the ground.
• There is coal in Antarctica – coal comes
from decaying tropical swamp land. If
Antarctica was a swamp land then it must
have been in another location on the earth.
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Quick Check
1. What did Wegener notice about the shapes of continents that led him to suggest that
continents were able to move?
______________________________________________________________
_______________________________________________________________________
2. List three forms of evidence besides continent shape that gave support to the idea of
continental drift.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Continental drift theory
- Pangea breaking apart
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How Can Continents Move?
• Wegener’s evidence for continental drift didn’t explain
how entire continents could change locations.
 New scientific equipment ( ________) allowed scientists to measure
the slow, but steady, drift of Earth’s tectonic plates.
 It was noted that ____________ and ____________ appear in certain
patterns, which happen to be along the ______________________
___________________.
 Mapping of the ocean floor revealed the __________________, a long
mountain range running down the middle of the Atlantic ocean.
See pages 510 - 512
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How Can Continents Move?
 Rocks taken from the Mid Atlantic ridge were ______________
than other ocean rocks.
 Sediments along the Ridge became ________________________
____________ from the ridge.
 _______________________ shows that iron-based rocks along
the ridges are striped with reversing magnetic fields.
All of these findings developed the
Theory of _______________________
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Sea Floor Spreading
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Sea Floor Spreading: An Explanation
• Hess suggested that magma rose to form new rock at certain places.
 Magma (melted rock), rises and falls like warm and cold liquids.
 The __________________________________ formed a
_______________________ where it broke through Earth’s crust.
 Like a “new crust” conveyer belt
 Magnetic striping of basalt rock shows long stripes of new rock
moving away from ocean ridges, and also reveals the direction of
Earth’s magnetic field at that time. This magnetic field changes or
reverses over time.
See pages 512 - 513
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• Wilson then unified the ideas of Wegener and Hess into the plate
tectonic theory.
 Continental drift occurs because of areas like these ridges, that
push along tectonic plates floating on Earth’s surface.
 geologic ______________ are anywhere magma rises to Earth’s
surface.
• A geologic hot spot is the location of ____________________, causing
magma to rise to Earth’s surface.
– The __________ Islands formed as a tectonic plate passed over a hot
spot and magma rose up from under Earth’s surface.
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Plate Tectonics - 1960
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Quick Check
Quick Check
1. Explain the implications of evidence from each of the following areas.
(a) mapping the sea floor _________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
(b) analyzing ocean rock and sediments _____________________________________________
____________________________________________________________________________
____________________________________________________________________________
(c) paleomagnetism _____________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
2. How did the Hawaiian Islands form? _________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
3. What does the theory of plate tectonics state? _________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
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