Introduction to Plate Tectonics

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Introduction to Plate Tectonics

• Alfred Wegener
• Continental Drift

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QOD

• How has Earths Surface changed over time?
• What processes change Earths Surface?

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Early Thoughts on the Motion of Continents

• 1596 -- Abraham Ortelius a Dutch map-maker in
  Thesaurus Geographicus.
• the Americas were "torn away from Europe and
  Africa . . . by earthquakes and floods"
• "The vestiges of the rupture reveal themselves,
  if someone brings forward a map of the world and
  considers carefully the coasts of the three
  continents.

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1858-- Antonio Snider-Pellegrini

• Geographer
• Maps show his version of how the American and
  African continents may once have fit together,
  then later separated.
• Left The formerly joined continents before their
  separation.
• Right The continents after the separation.
• (Reproductions of the original maps courtesy of
  University of California, Berkeley.)

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Continental Drift

• 1912 the full-blown scientific theory of
  Continental Drift
• Alfred Lothar Wegener -- a 32-year-old German
  meteorologist
• Studied evidence from all the Earth Sciences
• Proposed the supercontinent Pangaea
• Supporter Alexander Du Toit, Professor of
  Geology at Johannesburg University
• Named Laurasia and Gondwanaland

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Activity

• You are going to map Wegners Evidence
• Fit of the continents
• Fossils
• Climate
• Rock types and mountain ranges
• Answer the questions at the end of the activity
  for homework tonight.

7
QOD

• Describe the orientation of continents 250
  million years ago.
• How has the orientation changed?

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• Pangaea -- a supercontinent began to split up 200
  million years ago.
• Pangaea first broke into two large continental
  landmasses
• 1) Laurasia in the northern hemisphere
• 2) Gondwanaland in the southern hemisphere.
• Laurasia and Gondwanaland continued to break
  apart into the various smaller continents that
  exist today.

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Wegener's Evidence

• fit of the South American and African continents
• unusual geologic structures on both continents
• plant and animal fossils found on the matching
  coastlines of South America and Africa.
• it was physically impossible for most of these
  organisms to have swum or have been transported
  across the vast oceans.
• the presence of identical fossil species along
  the coastal parts of Africa and South America was
  the most compelling evidence that the two
  continents were once joined.

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A Explanation for many Observations

• The break-up of Pangaea also explained
• the evidence of dramatic climate changes on some
  continents.
• fossils of tropical plants in coal deposits in
  Antarctica
• distinctive fossil ferns (Glossopteris)
  discovered in now-polar regions
• glacial deposits in present-day arid Africa,
  such as the Vaal River valley of South Africa.

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Convincing Others

• The scientific community firmly believed the
  continents and oceans to be permanent features on
  the Earth's surface.
• Wegeners proposal was not well received

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The Fatal Weakness

• There was no explanation for the kind of forces
  that would be strong enough to move such large
  masses of solid rock over such great distances.
• Wegener -- continents plowed through the ocean
  floor
• Harold Jeffreys, a noted English geophysicist,
  disagreed
• it was physically impossible for a large mass of
  solid rock to plow through the ocean floor
  without breaking up.

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Wegeners Death

• He devoted the rest of his life to find
  additional evidence to defend his theory.
• He froze to death in 1930 during an expedition
  crossing the Greenland ice cap
• After his death, new evidence from ocean floor
  exploration and other studies rekindled interest
  in Wegener's theory, ultimately leading to the
  development of the theory of plate tectonics.