1. Plate Tectonics

2. Evidence for Continental Drift
Section 1
Evidence for
Continental Drift

3. Puzzle All of the continents look like they fit together on a map.
This was proposed by Alfred Wegener.

5. Pangaea
Wegener proposed this landmass broke apart about 200 million years ago (mya).
He called this landmass Pangaea, which means “all land.”

8. Fossil Clues
Mesosaurus fossils have been found in South America and Africa.
Mesosaurus is a freshwater swimming reptile.
The only way they could have been on different continents is if they were joined at one time.

11. A Widespread Plant
A plant called the Glossopteris, has had fossils found in Africa, Australia, India, S. America, and even Antarctica.
This supports that these places were once connected and had similar climates.

13. Climate Clues
This is evidence that it was once in a warm-weather climate and drifted to a cold-weather climate.
There is also evidence of glaciers in Africa, S. America, India, and Australia.

15. Clues in Rocks
If the continents were once connected, the rock formations where they connected would be similar.
The Appalachian Mtns. Are similar to those found in Greenland and W. Europe.
Rock structures from Africa and S. America are similar.

17. Section 2
Seafloor Spreading

18. Seafloor Spreading Harry Hess proposed that the seafloor is spreading.
The hot, less dense material below Earth’s crust rises toward the surface at Mid-Ocean Ridges.
This causes the seafloor to spread.

19. Evidence of Spreading
A research ship called the Glomar Challenger began drilling the seafloor to obtain rock samples.
They discovered that the youngest rocks are located at the Mid-Ocean Ridges
As they moved away from these Mid-Ocean Ridges, the rocks became progressively older.

20. Magnetic Clues
The earth has a magnetic field (the north pole and south pole).
The direction of the magnetic lines will occasionally reverse.
This is called a Magnetic Reversal
These Magnetic Reversals are recorded in the rocks forming along the Mid-Ocean Ridges.

21. Theory of Plate Tectonics
Section 3
Theory of Plate Tectonics

22. Plate Movements
According to the theory of Plate Tectonics, Earth’s crust and part of the upper mantle are broken into sections called plates.
These plates move on the “plastic like” layer of the mantle.

23. Composition of Plates Lithosphere—The earth’s crust.
Asthenosphere—The “plastic like” layer below the lithosphere.
The rigid plates of the lithosphere move around on the asthenosphere.

24. Plate Boundaries Divergent Boundary Convergent Boundary
Subduction Zones
Transform Boundary

26. Divergent Boundary
When the boundary between two plates is moving apart.
This is evident in the Mid-Ocean Ridges.
The N. American Plate is moving away from the Eurasian Plate.
The Great Rift Valley in Africa is a divergent boundary.

30. Convergent Boundary When two plates move together (or come together).
The Himalaya Mnts. Are formed by the collision of the Indo-Australian Plate and the Eurasian Plate.
The Andes Mnts. Are also formed by two convergent boundaries

31. Subduction Zone
When an oceanic plate converges with a less dense continental plate, the denser oceanic plate sinks under the continental plate.
Volcanoes often form above subduction zones.

32. Mt. Saint Helens Before and After

35. Where Plates Collide
A subduction zone can also occur where two oceanic plates collide.
In this case, the older, denser plate bends and sinks down into the mantle.
When two continental plates collide, they crumple up and mountains are formed.

36. Transform Boundary When plates slide past one another.
This can occur when the plates move in opposite directions.
It can also occur when the plates are moving in the same direction, but at different speeds.

37. Transform Boundary
When a plate slips past another suddenly, earthquakes occur.
The San Andreas Fault is an example of a Transform Boundary.

40. Causes of Plate Tectonics
Convection Current
When hot, less dense rock is forced upward by the surrounding cooler rocks.

41. How to write a Cinquain

42. 1st line—one word
Subject

43. 2nd line—two words
describe

44. 3rd line—three words
action

45. 4th line—four words
Describe

46. 5th line—one word
summary

47. ORQ
Most scientists believe that there was a super-continent named Pangaea.
A. How long ago did this super-continent exist?
B. Give 3 pieces of evidence that this super-continent existed.