1. Continental Drift

2. Plate Tectonics  The lithospheric plates float on top of the liquid asthenosphere.  This causes the plates to move around slowly.  Over a long period of time, they can move large distances.  The lithospheric plates float on top of the liquid asthenosphere.  This causes the plates to move around slowly.  Over a long period of time, they can move large distances.

3. Discovery  Alfred Wegener was the first person to come up with the concept of Continental Drift.  He suggested that the continents formed from a super-continent called Pangaea, breaking apart about 200 million years ago  Alfred Wegener was the first person to come up with the concept of Continental Drift.  He suggested that the continents formed from a super-continent called Pangaea, breaking apart about 200 million years ago

4. We are now going to look at the pieces of Evidence Wegener used to prove his theory…

5. 1. Jigsaw Puzzle  Wegener’s first clue was the perfect fit of the African/South American Coastlines

7. 2. Geological Structure  Analysis of rocks suggested similarities between continents (similar age/type)  Some mountain ranges end at one coastline and begin at another  Analysis of rocks suggested similarities between continents (similar age/type)  Some mountain ranges end at one coastline and begin at another

8. 3. Fossil Evidence  This is the best support for Wegener’s theory  Similar fossils have been found in different locations across the world  Eg. Mesosaurus  The only explanation: all the land was once connected  This is the best support for Wegener’s theory  Similar fossils have been found in different locations across the world  Eg. Mesosaurus  The only explanation: all the land was once connected

10. 4. Glacier Evidence  (Paleoglaciation)  When glaciers move, they leave distinctive patterns  (large U shaped valleys, sediments, deep scratches)  All of these were found in tropical areas  (Paleoglaciation)  When glaciers move, they leave distinctive patterns  (large U shaped valleys, sediments, deep scratches)  All of these were found in tropical areas

11. 5. Coal Beds  Coal beds form from the decomposition of tropical swamps  So how can there be coal beds in Antarctica?  Coal beds form from the decomposition of tropical swamps  So how can there be coal beds in Antarctica?

12. The best answer for the coal/glacier evidence is that the continents must have been in completely different locations, which gave them completely different climates!

13. The only question Wegener couldn’t answer was…  How can continents move if they are large and made out of solid rock?  Plate tectonics and the soft asthenosphere were unknown at the time so he had no answer…  How can continents move if they are large and made out of solid rock?  Plate tectonics and the soft asthenosphere were unknown at the time so he had no answer…

14. Plate Tectonics

15. Proof – Magnetism The discovery of the mid-atlantic ridge (which is a mountain range under water)  It has bands of opposite polarity called magnetic striping  See p512 The discovery of the mid-atlantic ridge (which is a mountain range under water)  It has bands of opposite polarity called magnetic striping  See p512

16. Explanation of Striping  Earth is like a bar magnet. It flips polarity every 500,000 years.  As the ridge opens, it makes new rock. As the rock hardens, its domains line up with the earth’s magnetic field.  Earth is like a bar magnet. It flips polarity every 500,000 years.  As the ridge opens, it makes new rock. As the rock hardens, its domains line up with the earth’s magnetic field.

17.  As the earth’s magnetic polarity flips, so does that of the rock.  This creates magnetic stripes.  As the earth’s magnetic polarity flips, so does that of the rock.  This creates magnetic stripes.

18. Sea Floor Spreading  Harry Hess  Magma is less dense so it rises through breaks in the sea floor  We call this spot a spreading ridge  It cools and hardens, making new sea floor  Harry Hess  Magma is less dense so it rises through breaks in the sea floor  We call this spot a spreading ridge  It cools and hardens, making new sea floor

19. This process continues, pushing older rock aside. We call this process sea floor spreading

20. Plate Tectonic Theory  J. Tuzo Wilson  Island arcs form when plates move over stationary hot spots  This is an area where molten rock rises.  He helped form the Plate Tectonic Theory  J. Tuzo Wilson  Island arcs form when plates move over stationary hot spots  This is an area where molten rock rises.  He helped form the Plate Tectonic Theory