1. Earth Shaping Chapter 16

2. Earth Shaping Theory   It was a gradual change over time.   In early 1900’s Alfred Wegener proposed the theory of continental drift.   Scientist DID NOT support his theory because at that time he could not explain his theory.

3. Current Continental Drift Theory   The earth is constantly changing. In addition to the effects of weathering and erosion, there are much larger scale changes occurring due to the movement of large plates in the lithosphere.

4. HOW DO WE KNOW THIS?   Wegener developed his idea based upon 4 different types of evidence:   1. Fit of the Continents   2. Fossil Evidence   3. Rock Type and Structural Similarities   4. Paleoclimatic Evidence

5. Earth’sLayers Inner Core - made of iron Outer Core–molten(liquid) Mantle – most of Earth’s mass Crust- rocky and brittle, can fracture

6. How do we know?  Measuring seismic waves  The speed of the wave determines the type of rock it is traveling through  Do waves travel faster in solids or liquids?

7.  TWO TYPES OF CRUSTS:  Oceanic – thin, dense rock  Continental- thick, low density LITHOSPHERE- Outer part of the crust; divided into tectonic plates ASTHENOSPHERE- the tectonic plates are on the asthenosphere

8. Plate Movement  Continental Drift – the movement of the tectonic plates  Theory -  that continents drift apart  *Proposed by Alfred Wegner  *Fossil evidence 

9. Sea Floor Spreading  Magma Rises in mid –ocean ridges or cracks called fissures  1. Forms new crust  2. Moves horizontally  3. Older crust moves further out

10. Magnetic Reversals  Earth’s north and south magnetic poles change places  Can be seen in the oceanic crust  Magnetic minerals align with magnetic field

11. Supercontinent  Pangea – all of the continents were joined together  Gradually drifted apart over time.

12. Plate Tectonic Theory 3 Possible Forces  Ridge Push  Convection  Slab pull/Subduction

13. Ridge Push –  gravity causes oceanic crust (lithosphere) to sink, subsidence

14. Convection Slab Pull  Hot rock rises while cool rock sinks  Causes the lithosphere to move sideways  Subduction Zone- when oceanic lithosphere (crust) is more dense causing the edge to sink and pull the rest of the plate with it

15.  African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates. 7 Tectonic PlatesMOVEMENT: *Different directions & speeds *2-10cm per year (the speed your fingernails grow)

16. Plate Boundries  Convergent – come together  Divergent – pull apart  Transform – slide past each other

17. Review  Magma moves in _______  currents due to change in temperatures.  convection

18.  When rock layers come together it is a ________  boundary.  When they pull apart it is a  _________ boundary.  boundary. convergent divergent

19.  Tectonic plates are large pieces of ___________  A rock is made of 2 or more ____________ lithosphere minerals

20. 1 2 3 What rock type is at 1? What rock type is at 2? What rock type is at 3?