1. Continental Drift, Seafloor Spreading & Plate Tectonics
Standard 3
(pink test review packet)

2. Continental Drift
Earth’s continents were once joined as single landmass; broke apart and continents drifted to present position
Pangaea: supercontinent (break up ~ 200 mya)
Wegner
Not accepted - lack of mechanism for the movement of continents (why and how)

4. Evidence for Continental Drift
Jigsaw puzzle fit of continents (S.A. & Africa)
Rock formations on different continents – same age, similar structure
Fossils of land dwelling animals on different continents
Climate – coal beds (form in humid swamps) found in Antarctica & tropical plants

5. Seafloor Spreading New oceanic crust forms at mid-ocean ridges
Destroyed at subduction zones (deep-sea trenches)
Magma rises, forced upwards, lava fills in ridge, hardens and new seafloor moves away from the center of the ridge.

6. Evidence for Seafloor Spreading
Discovery of mid-ocean ridges
Seafloor youngest at mid-ocean ridges
Magnetic pattern is the same on both sides of the ridge (mirror image)
Hess
Technology: Sonar (uses sound waves)

8. Theory of Plate Tectonics
Earth’s crust and rigid upper mantle are broken into tectonic plates
Movement of plates creates most volcanoes and major mountain ranges
Movements cause earthquakes
Plates move because of Convection in the mantle

10. Types of crust/plates Continental Crust Oceanic Crust Older Lighter
Granite
30 miles thick
Oceanic Crust
Younger
Denser
Basalt
5 miles thick

11. Plate Boundaries
Divergent
convergent
transform

12. Divergent Plates move away from each other
Most found on seafloor (mid-ocean ridges)
Found on continental crust – stretches crust to form a rift valley (African Rift Valley)
Shallow earthquakes

13. Convergent Plates move towards each other Crash or collide
3 types based on type of crust

14. Convergent Boundaries: plates converge/collide
Continental – continental
high mountain ranges
Himalayas
Continental – oceanic
volcanic mountain ranges on land, deep-sea trenches
Cold more dense plate sinks
Andes, Cascades
Oceanic – oceanic
volcanic islands, deep-sea trenches
Colder, denser plate sinks
Mariana Island, Japan

16. Transform Boundaries Two plates slide past each other
Example – San Andreas fault

17. Mantle Convection
Convection: hot less dense material rises & cold, denser material sinks
Magma rises because it is less dense than surrounding rock & it forces itself upwards
Driving force of plate tectonics

19. HOT SPOTS Some volcanoes form over hot spots
As tectonic plate moves chain volcanoes form
Hawaiian Islands – Kilauea located over hot spot
Yellowstone located over hot spot