1. Warm- Up Ch. Mid term questionsTOC: 106. Tectonic Proof 107. Ocean floor 108. Pg 275 (1-17) Keywords:  Paleomagnetism  Hot spot  Convection current  Slab- pull  Ridge- push

2. Quiz 1. What are the 3 major zones of Earth according to chemical composition? 2. What are the two types of crust and which is igneous rock is each mostly made of? 3. Provide the 4 pieces of evidence presented by Wegener to defend continental drift. 4. Which later of Earth contains the greatest volume and what percentage of Earth’s volume does it make up? 5. What are the 2 metals that make up the core?

3. Quiz 6. Put the following in order of increasing density: outer core, continental crust, asthenosphere, oceanic crust, 7. What are the 3 types of convergent boundaries? 8. At which type of boundary is crust neither created nor destroyed? 9. If two oceanic plates collide, which plate will go under the other and what is the name for this process? 10. How much water is believed to be in the mantle?

4. Plate Tectonics  Dozen or so plates in constant movement  3 different ways plates can interact  Worked to explain why continental drift occurred

5. Proof  Scientists immediately began testing the new model.  There was evidence to support continental drift.  Seafloor spreading was observed for plate tectonics.  Paleomagnetism would seal the deal

6. Paleomagnetism  Earth’s magnetic field is felt by magnetic materials  Lava is too hot to be affected but as the rock cools, the poles align  Rock points to current poles at time of becoming solid

7. Paleomagnetism  Sometimes the poles will “flip”  During these times the magnetic moment of the rock formed will be in another direction  Flipping of poles is not dangerous  Occurs 3-4 times per million years

8. Earthquake Patterns  Plate tectonics was supported by the occurrence of deep- focus earthquakes in areas of deep ocean trenches  Plate boundaries coincide with earthquake zones  Slab movement can be followed down to 700Km

9. Ocean Drilling  Deep Sea Drilling project (68- 83) brought up samples; older as distance from boundary increased  Confirmed hypothesis of seafloor spreading  Youngest crust near ridge; oldest closer to continents  Ocean crust up to 180 million years old while continental is up to 4 billion

10. Hot Spots Prove they move Plate dragged across mantle plume Oldest islands furthest away.

11. But How  Can’t travel below plates  How do we prove the plates move if we don’t know the cause?  Evidence was enough to build theory  Convection currents are believed to be the main cause

12. Convection Currents  Material near the crust becomes more dense, causing it to sink  Sinking material flushes less dense material up  Cyclical process  Creates conveyor belt in the asthenoshere

13. Slab- Pull  Plates have enormous mass.  Once subduction begins, plate is pulled to the center of Earth

14. Ridge- Push  Material forms at the ridge and hardens  New material is pulled by gravity down the slope of the ridge  LEAST POWERFUL OF THE FORCES

15. Assignment  Complete pages 273- 274 with a partner; there is no worksheet just record your measurements in your notebook.  For homework complete page 275 (1-17) short answers are fine.