3. Alfred Wagner – proposed that in the distant past, the Earth ’ s continents were all joined as a single landmass. What was the name of his hypothesis? Continental Drift

4. Evidence of Wagner’s Theory 1. Landforms Fit like a Puzzle *Pangaea *Pangaea – when Wegener placed all the continents together like a puzzle, it formed a large landmass which he called Pangae 2. Matching of Fossil & Ancient Rock *Glacial Till Deposits – glaciers from South Africa & North Australia 3. Climate Evidence in Rock Layers: South America, Africa, India, Antarctica, and Australia show remarkable similarities Same three layers in the same order in areas TODAY are separated by oceans.

5. Wegener named Pangea: -the Southern portion Gondwana -the Northern portion Laurasia “Puzzle” of Continents Over Time

6. Why was Wagner’s theory not accepted? Wagner could not explain the forces that caused the continents to move. (mechanism of movement) Most Scientists believed that Earth was solid and immovable.

7. What two Scientists had evidence to support Wagner’s theory? -Arthur Holmes Thermal convection in mantle “move” continents – Harry Hess  Using radar (new technology) he discovered the seafloor has trenches and mid-ocean ridges Proposed Sea-floor Spreading Theory –Led into Plate Tectonics…

8. What is Sea-floor Spreading?

9. So…as Seismic Technology Advanced: Wagner’s Theory was Proven Layers of the Earth were identified: – Lithosphere, Asthenosphere, Mantle, Inner/Outer Core, Crust Layering based on: – Density – Chemical Composition – Mechanical Behavior of Material

10. The Outer & Inner Core The Outer Core *liquid layer of very hot metals *Main Minerals/Metals: *Mostly Iron, some nickel The Inner Core *Solid layer due to extreme pressure *temperature greater than 6,000 C

11. The Core The way in which P waves are refracted within the earth ’ s core suggests that the core has two parts, a liquid outer core and a solid inner core WHY??

12. The Mantle -Largest layer of the Earth *29,000 km thick *67% of Earth’s mass -Beneath the crust -Main Elements: *Oxygen, Silicon, Magnesium, Iron, Aluminum -Made of Magma * very hot dense rock that flows -The movement of the upper mantle (asthenosphere) is the reason that the crustal plates of the Earth move.

13. Studying the Mantle Scientists cannot observe the mantle directly SO how do they study the mantle?? Using Observations made from Earth’s surface: Data from Earthquakes and Volcanic Eruptions S Waves & P Waves Studying Magma Studying the Ocean Floor Lava – Molten rock(magma) that reaches Earth’s surface

14. The Crust Made of Light, brittle rocks Main Elements: – Oxygen – Silicon – Aluminum Very thin in comparison to the other three layers – like the skin of an apple. It is. Only 1% Earth’s mass. Two types of crust: – Continental – Oceanic

15. The Crust: Two Main Kinds 1. Continental crust -- under the continents -lighter, older, thicker, mostly granite. -About 25 miles (32 kilometers) thick 2. Oceanic crust -- under the oceans -twice as much iron, magnesium, and calcium as continental -mostly basalt.-much denser than the granite -3-5 miles (8 kilometers) thick under the oceans **the less dense continents ride on the more denser oceanic plates.

16. What are differences between oceanic crust and continental crust? 1. The continental crust is composed of granite while the oceanic crust is composed of basalt. 2. The density of the continental crust is less than the oceanic crust, thus it floats higher on the mantle.

17. Tectonic Plates Lithosphere- *Crust and rigid upper part of the mantle *Similar to giant jigsaw puzzle *Each “piece” is Tectonic Plate – large section of lithosphere that is in slow, constant motion Asthenosphere- * soft, semi-rigid layer within the upper mantle that flows like a thick liquid *Tectonic plates "float” or move on the asthenosphere

18. Convection Currents * caused by very hot MAGMA at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over *The middle mantle "flows" because of convection currents. *This movement beneath the plates causes the plates to move

19. Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration. Safety Caution: Don’t get your face too close to the boiling water! *Use your knowledge…how do you think a convection oven cooks food?

21. Plate Boundaries Around the World

22. Review: The Layers of the Earth The Earth is composed of how many layers? 1. crust -layer that you live on --most widely studied and understood. 2. mantle - much hotter -has the ability to flow. 3. outer core and inner core -- - -hottest layer -high pressure

23. *In which layer is most of the mass of the Earth located? The Mantle *The mantle increases in temperature depending on how close it is to _______. The Core The rocks in the ____ mantle are brittle and break while the rocks in the _____mantle are soft and flow instead of break. Upper; Lower

24. The core is thought to be composed of ___ & ____. *nickel and iron Which core layer is liquid? *Outer Which core layer is solid? *Inner What causes the Inner core to be solid? * Tremendous pressure, produced by the weight of the overlying rocks

25. Review Time: What is the Lithosphere? – The crust and part of the upper mantle – 100 km thick Why does it float? – Less dense than the material below it so it “floats” What is the Asthosphere? – Softer layer of the upper mantle that flows What process causes the asthenosphere to flow? – Convection Current