Plate Tectonics and Continental Drift

1
Plate Tectonics and Continental Drift
2
Continental Drift

• Alfred Wegener believed that the continents were
  once connected.
• This large continent was called Pangea.
• In 1915, he proposed his theory of Continental
  Drift.

3
Evidence For Continental Drift

• Matching fossils were found along the boundaries
  of continents that have very different climates.
• Glacial deposits found in South America, Africa,
  India, and Australia.

4
Sea Floor Spreading Theory

• With sonar, scientists determined that the ocean
  floor was composed of mountains and deep valleys.
• Harry Hess authored the Sea Floor Spreading
  Theory to explain that the ocean floor is
  constantly spreading along the Mid-Atlantic
  Ridge.

5
Mid-Atlantic Ridge

• New sea floor is created by oozing magma in the
  center of the MAR.
• Old sea floor is forced down into the mantle in
  the trenches near the boundaries of the oceans
  and continents.
• Rocks near the MAR were much younger than rocks
  that had been forced outward from the MAR.

6
Plate Tectonic Theory

• A new theory based on the Sea Floor Spreading
  Theory and The Continental Drift theory were
  combined to form the Plate Tectonic Theory.
• Plate Tectonic Theory States that the earths
  crust and upper mantle are broken into sections
  called plates. The plates move around on the
  mantle.