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Continental Drift and Sea Floor Spreading

Continental Drift and Sea Floor Spreading. Chapter 17. Continental Drift. In 1912 Alfred Wegener came up with the hypothesis The continents were all one Called Pangaea. Continental Drift. Pangaea Super continent Existed during the Permian Period North half called “Laurasia”

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Continental Drift and Sea Floor Spreading

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  1. Continental Drift and Sea Floor Spreading Chapter 17

  2. Continental Drift • In 1912 Alfred Wegener came up with the hypothesis • The continents were all one • Called Pangaea

  3. Continental Drift • Pangaea • Super continent • Existed during the Permian Period • North half called “Laurasia” • South half called “Gondwanaland”

  4. Continental Drift • Wegener had 4 major pieces of evidence for his theory • Similar rocks found in Africa and South America • Glaciation and Ancient Climates • Fossils • Continents seem to fit like puzzle pieces

  5. Continental Drift 1. Similar Rocks in Africa and South America • Rocks on both coasts are the same kind • 2 continents must have been joined when rocks formed

  6. Continental Drift 2. Glaciation/Ancient Climates • During Carboniferous period • Glaciers in India, South Africa, South America and Australia • Northern hemisphere was warm and tropical

  7. Continental Drift • Fossils • Mesosaurus = aquatic (shallow) reptile

  8. Continental Drift 3. Fossils • Glossopteris = fern that liked cold climates that has large seeds that do not spread out well

  9. Continental Drift 4. Continents fit like puzzle pieces • First looked at South America - looked like it would fit like a puzzle piece into Africa • Most continents fit together

  10. Continental Drift • Wegener tried to explain why and how the continents moved • He thought that the continents plowed through the ocean floor • This was physically impossible • So the other scientists of the time didn’t believe him

  11. Sea Floor Spreading • Enter Harry Hess (1962) • Naval Officer • Used Fathometer (measures depth) • Took a map of the sea floor • Noticed mountains and valleys in the ocean

  12. Sea Floor Spreading • He proposed a theory to explain mid-ocean ridges • The magma wells up from deep inside the Earth and forms new rocks. • Some rocks contain minerals that are magnetic. • When the rock forms it records the direction of Earth’s magnetic field. • Like a compass, the rocks “point” towards magnetic north. • From the rocks we know that the earth’s magnetic field has reversed over time.

  13. Sea Floor Spreading • From this theory, he could estimate age of land • And the speed of movement of plates • Noted that if new crust is formed, there must be a place where old crust is destroyed • It is a continuous cycle • Even though new crust is forming, the Earth remains the same size!

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