1. Where did the idea come from that the continents were once connected?
As long ago as 1620, the English thinker Francis Bacon noticed similarities between the coasts of South America and Africa.

2. What is continental drift?
Continents were once connected into one supercontinent and have since drifted to their current positions
Alfred Wegner developed the idea in 1912
He called the supercontinent Pangaea

3. Stretched from pole to pole Centered where Africa is today
PANGAEA (greek: pan = _____, gaea = ________)
Stretched from pole to pole
Centered where Africa is today
all
land

5. Wegner’s Evidence Supporting Continental Drift
Coastlines
Landforms
Fossils
Climate

6. Continental Drift Evidence Coastlines
Coasts of some continents look like they fit together.
Example: east coast of South America and west coast of Africa

7. Continental Drift Evidence Landforms
Mountain ranges on different continents line up
Similar coal and rock formations found on different continents line up; are same age
Example: Appalachians line up with the mountain ranges in Europe. They are the same type of rock and age.

8. Continental Drift Evidence Fossils
Fossils of the same organisms are found on different continents
Mesosaurus

10. Continental Drift Evidence Climate
Evidence of past tropical climates in the Antarctic
Example: fossils of Glossopteris (tropical plant) found in areas that are now colder

11. Continental Drift Evidence Climate
Evidence of past tropical climates in what is now the Antarctic
Evidence of glacier marks in what is now the tropics
Continental Drift

23. Why was the idea of continental drift rejected for more than 40 years?
Wegner could not provide the force that caused the continents to move. How could huge solid chunks of land have plowed through the ocean floor???

24. What Is the Theory of Plate Tectonics?
Pieces of Earth’s lithosphere are in constant slow motion; driven by convection currents in the asthenosphere
Explains creation, movement, destruction of Earth’s plates

25. What Are Plates and Plate Boundaries?
Plates: broken pieces of the lithosphere
Plate boundaries: the edges of the plates

27. What Happens at Plate Boundaries?
Plates can pull away from each other
Divergent boundaries
Plates can grind past each other
Transform boundaries
Plates can crash into each other
Convergent boundaries

28. Divergent Plate Boundary
A place where two plates move apart or divide
Crust is created from cooled magma

29. What geologic features form at divergent plate boundaries?
Mid-ocean ridges
divergent plate boundaries beneath the ocean
world’s longest mountain range!
circle Earth like a seam on a baseball
Example: Mid-Atlantic Ridge

32. Volcanoes

33. http://www. smithsonianmag

34. Eldfell in Heimaey

35. What geologic features form at divergent plate boundaries?
Rift valleys
divergent plate boundaries on land
Examples: Rio Grande Rift (North America), Great Rift Valley (East Africa)

38. http://www. getintravel

39. Transform Plate Boundary
A place where two plates grind past each other, moving in horizontal opposite directions
Crust is neither created nor destroyed

40. What geologic features form at transform plate boundaries?
Responsible for creating strike-slip faults, which lead to strong earthquakes
Example: San Andreas Fault (Calif.)

42. San Andreas Fault

45. Convergent Plate Boundary
A place where two plates come together
Crust is destroyed due to subduction (edge of plate sinks under another plate into the mantle)
Collisions happen between:
Oceanic/Continental
Oceanic/Oceanic
Continental/Continental

46. What geologic features form at convergent plate boundaries?
Collision between oceanic crust and continental crust
basalt (oceanic crust) more dense than granite (continental crust)
forms deep ocean trenches where ocean crust is subducted into mantle
forms volcanoes on continent due to melting crust
Examples: Andes, Cascades, Sierra Nevada

47. DEEP-OCEAN TRENCH
Link to
Simulation
Subduction
&
Volcanic eruption

48. What geologic features form at convergent plate boundaries?
Collision between oceanic crust and oceanic crust
forms deep ocean trenches where one ocean crust is subducted under the other
forms volcanic arc islands
Examples: Aleutian, Tonga, Mariana Islands

49. Link to
Simulation

50. What geologic features form at convergent plate boundaries?
Collision between continental crust and continental crust
forms high mountain ranges
Examples: Himalayas

51. Link to
Simulation

52. Collision of India and Asia