1. Plate Tectonics: Boundaries!

2. Review Main objection to Wegener's proposal
Wegener - continental drift hypothesis
4 lines of evidence
Continental puzzle
Fossil records
Matching mountain ranges
Ancient climate
Main objection to Wegener's proposal
Inability to provide a mechanism

3. Earth’s internal structure
Earth’s internal layers can be defined by
Chemical composition
Physical properties
Layers defined by composition
Crust
Continental
Oceanic
Mantle
82% of the volume
Core

4. Density The physical property that ties most things on earth together?
What type of processes does density effect?
Formation of the earth
Anything that works through convection currents
Plate movements
Wind and ocean currents
Weather
Erosion + Weathering

5. Earth’s internal structure
Four main layers of Earth are based on physical properties and hence mechanical strength
Lithosphere
Asthenosphere
Mesosphere
Core

6. Earth’s internal structure
Asthenosphere
Exists beneath the lithosphere
Hotter and weaker than lithosphere
Allows for motion of lithosphere
Plate boundaries
All major interactions among plates occur along their boundaries

7. Plate Boundaries Types of plate boundaries
Divergent plate boundaries (constructive margins)
Convergent plate boundaries (destructive margins)
Transform fault plate boundaries

8. Divergent plate boundaries
Divergent plate boundaries (constructive margins)
Two plates move apart
Mantle material upwells to create new seafloor
Ocean ridges and seafloor spreading
Oceanic ridges develop along well-developed boundaries
Along ridges, seafloor spreading creates new seafloor

9. Divergent boundaries They are located mainly along oceanic ridges
Figure 15.10

10. Divergent boundaries Some are found on land The East African rift
Within a continent, continental rifts form at spreading centers

11. Convergent plate boundaries
Convergent plate boundaries (destructive margins)
Plates collide
An ocean trench forms and lithosphere is subducted into the mantle

12. An oceanic-continental convergent plate boundary
Oceanic-continental convergence
Denser oceanic slab sinks into the asthenosphere
Pockets of magma develop and rise
Continental volcanic arcs form
Examples include the Andes, Cascades, and the Sierra Nevadan system

13. An oceanic-oceanic convergent plate boundary
Two oceanic slabs converge and one descends beneath the other
Often forms volcanoes on the ocean floor
Volcanic island arcs forms as volcanoes emerge from the sea
Examples include the Aleutian, Mariana, and Tonga islands

14. A continental-continental convergent plate boundary
When subducting plates contain continental material, two continents collide
Can produce new mountain ranges
Figure C

15. The collision of India and Asia produced the Himalayas
Before
After
Figure A

16. Transform fault boundaries
Plates slide past one another
No new crust is created or destroyed
Most join two segments of a mid-ocean ridge
Aid the movement of oceanic crustal material