Continental Drift Theory hits a Dead End

1
Continental Drift Theory hits a Dead End

• (or does it?)

2
Support for Wegeners CDT

• Jigsaw Evidence
• Fossil Evidence
• Rock Evidence
• Climate-ological Evidence

3
Detractors said, But how?

• Wegener Continents plowed through the crust
• No evidence of fractures or buckling
• How did it happen? What caused it?
• The moon?
• The winds?
• ?
• Baby/Bathwater
• Out it went

4
Evidence from the Sea Floor

• Sonar
• Deep Sea Sediments
• Paleomagnetism

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Sonar

• Oceans floor thought to be flat and
  feature-less
• Sonar bounced sound waves off of ocean bottom and
  constructed pictures
• Showed ridges, long mountain chains, and deep
  trenches

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Mapping the Oceans Floor
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Deep Sea Sediments

• Took and analyzed samples of ocean floor/crust
• Oceanic crust is young
• 180 million years old vs. 3.5 billion for parts
  of land
• Crust is relatively young near ridges, and older
  farther away
• Sediments are shallow near ridges, deeper farther
  away

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Age of the Sea Floor Crust
Newer Older
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Paleomagnetism

• The study of the ancient record of the Earths
  magnetic field
• Iron-containing rocks (like basalt) have
  particles that point like a compass

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Approximately 1000 km difference
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Polar Wandering
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Magnetic Reversals

• From time to time, the Earths magnetic field
  switches poles
• Over the last 10 million years, its reversed
  about 4 or 5 times every million years
• Ocean floor shows banding pattern of magnetic
  anomalies
• Pattern is a mirror image on both sides of a ridge

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Mapping Magnetic Anomalies
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Tomorrow
Continental Drift Theory (CDT) Evidence from
the Ocean Floor __________________________________
__________________________________________ Plate
Tectonic Theory (PTT)