1. Warm-up
Which piece of evidence for plate tectonics do you think is most compelling and why?
Compelling: strong and forceful, having influence
You find an axe made of stone containing Uranium You determine it has undergone 7 half lives. What percentage of U-235 is remaining and how old is the axe? (Half life of U-235 is years)

2. Plate Boundaries

3. Plates and Boundaries Two types of crust: Oceanic crust
Continental crust
Three types of boundaries:
Convergent
Divergent
Transform
Fault – Crack in crust at border of plate boundaries
Demo with density blocks possibly…more dense object sinks. **

4. Convergent Boundary Plates collide
3 types based on types of crust colliding
1. Continental-continental
Create mountains
Examples
3 types of convergent boundaries based on types of crust of colliding plates
Continental – continental: example = India into Eurasian plate, a plate will subduct, but other buckles upward forming mountain ranges; creating the Himalayas today
Continental – oceanic: example = Pacific and North American plates in places, creates a subduction zone and trench as ocean crust sinks because it is more dense, oceanic crust is melted and recycled in the mantle, can also create volcanoes
Oceanic and oceanic: example = Pacific and Australian plates, one of them subducts

5. Convergent Boundary 2. Oceanic-oceanic 3. Continental-oceanic
Older plate is subducted (more dense)
Subduction forms trench
Volcanoes
Example
3. Continental-oceanic
Oceanic is subducted
Creates:
Trenches
1. Subduction Zone Volcanism -
2. Mt. St. Helen’s video in picture

8. Warm-up
Which layer of the Earth is responsible for the movement of tectonic plates?
The half-life of plutonium is 6530 years. A sample contains .39% of the original amount of plutonium. How many half- lives have passed and how old is it?
What do you think is the damage caused by earthquakes?

9. Transform Boundary Plates slide past each other Not a smooth movement
No creation or destruction of crust
Earthquakes!
San Andres Fault
Transform boundary: plates are sliding at angles past each other
Not smooth, gets stuck, builds up pressure and eventually releases that pressure in large bursts creating large earthquakes
Some rocks exhibit plastic behaviors which is more elastic, when under pressure it just keeps stretching and stays that shape, no earthquakes are formed (photo)
Elastic rebound hypothesis= stretch to breaking point, breaks, releases energy, return to original shape
Images are of the San Andreas Fault – top is of an orchard where the rows shifted due to earthquakes over the years

10. Warm-up
On the back of your Boundary worksheet, create a 2-circle Venn diagram to compare convergent and transform boundaries.
1. CT

11. Divergent Boundary Plates separate 2 types Space fills with magma
Creates new crust
Pushes old crust out
2 types
Rift zone = deep cracks between separating plates
Magma fills rift cracks due to lower density it rises up, cools and forms new crust

12. Divergent Boundary Continental-Continental or on Continental Plate
Creates rift valley
May become lake
Examples
Rift Valley, Africa
Map of divergent boundary in Africa
Land bridge over rift in Iceland

13. Iceland
Map of Iceland
A diver swims between the Eurasian and North American tectonic plates in Silfra Canyon,Thingvellir National Park, Iceland. In this photograph the American plate is on the left, and the Eurasian on the right.

15. Divergent Boundary Oceanic-Oceanic Spreading center Mid-ocean ridge
Majority of Earth’s volcanoes
Non-explosive
Map of oceanic ridges
A section of the mid-Atlantic Ridge where the African and South American Plates are created. A rift valley over a mile (2 km) deep marks the axis of the ridge. Depths range from 1900 (pink) to 4200 meters (dark blue). Image used with permission of Ken Macdonald.