History of Plate Tectonics

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History of Plate Tectonics

• Put Together by Kim Wright

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Whats the Pattern?
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What are Petosky stones?
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Why do we have tropical corals in Michigan?
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A Great Big Puzzle?

• 1912, Alfred Wegner
• Proposed theory of Continental Drift
• Recognized that the continents fit together like
  a puzzle.
• Put them together and called them Pangea

Pangea as visualized by Wenger
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What evidence was there?

• See your fossil maps
• Fossils of Mesosaurus appeared on opposite
  continents.
• Glossopteris leaves were found along all the
  southern continents.
• Rocks in South America and Africa showed the same
  marks from glaciers.

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How did Wenger think Continental Drift work?

• Wengers theory states that the centrifugal force
  from the rotation of the Earth forced the
  continents apart
• The Americas move west was because of the
  gravitational pull of the sun and the moon
• What do you think?

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REJECTED!

• What was good about Wengers theory?
• Wengers ideas were good, but he didnt have the
  mechanism right.
• The scientific community rejected his ideas
  saying that Centrifugal force of earths rotation
  was not strong enough to split continents.

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Holmes, I think youve got it!

• At the same time Wenger was doing his work,
  Arthur Holmes investigated another mechanism.
• Thermal convection in the mantle- (hot stuff
  rises, cool stuff sinks)
• No one listened to him until the 1940s and 50s
  because he didnt back up his theory with enough
  evidence?

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The Breakthrough

• World War II used instruments that mapped the
  ocean floor in many ways
• We talked about magnetic striping, to the left is
  a picture of this phenomenon.
• What do you think this told scientists?

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The Spreading Seas

• Matching magnetic anomalies on the sea floor told
  scientists it was spreading.
• How did this work?
• Get 2 sheets of notebook paper
• Fold one into a long strip and then into half
• In the other, cut a slit so that the width of the
  folded paper will fit through it.
• Wait for instructions.

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This led to the Plate Tectonics theory as we know
it today
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If the sea floor is expanding, the ocean is
getting bigger- does that mean the earth is
expanding?Why or why not?
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Questions a good, unifying theory must answer

• We know the earth isnt expanding, so what IS
  happening?
• Why do earthquakes seem to form a pattern?
• Why are most volcanoes located near the shores?
• What forms mountains?
• What is the driving force behind it all?

This map shows the pattern of earthquakes and
volcanoes across the globe
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Plate Tectonics Official Definition
1. The Earth's surface is covered by a series of
rigid, crustal plates that ride on the
lithosphere.
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Plate Tectonics Official Definition
2. The ocean floors are continually, moving,
spreading from the center,
sinking at the edges, and being regenerated.
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Plate Tectonics Official Definition
3. Convection currents beneath the lithosphere
move the crustal plates in different directions.
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Definitions to Know before next class

• Compressional tension
• Shearing tension
• Extensional tension
• Convergent plate boundary
• Divergent plate boundary
• Transform plate boundary

• Fault
• Rift
• Mantle Convection
• Subduction Zone
• Trench
• Hotspot
• Island Arc
• Lithosphere
• Asthenoshpere

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Transformshearing
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Additional Resources
http//www.msu.edu/wrigh138/pthistory.ppt (This
lecture) http//pubs.usgs.gov/publications/text/d
ynamic.html http//earthsci.terc.edu/navigation/c
hapter08.cfm http//earthsci.terc.edu/navigation/
chapter09.cfm http//earthsci.terc.edu/navigation
/chapter10.cfm http//earthsci.terc.edu/navigatio
n/chapter11.cfm