Forces that Shape the Earth

1. Forces that Shape the Earth State Correlation 4b

2. Plate Tectonics 1912 – German scientist Alfred Wegener Proposed two ideas that are known as Continental Drift Theory Earth’s continents were once joined in a single large landmass called Pangaea that broke apart Continents have drifted to their current location

3. Continental Drift It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations.

4. Evidence for Continental Drift • Puzzle-like fit of the continents • Similar fossils have been found on different continents • Arctic areas & glacier deposits in tropical areas • Similar rock structures are found on different continents

6. Seafloor Spreading • Wegner’s theory was not widely accepted because no one could explain how or why continents moved. • Using sound waves scientist discovered underwater mountain ranges called mid-ocean ridges • In 1960, Harry Hess suggested the theory of seafloor spreading

7. Mid-Ocean Ridges • Form underwater mountain chains where the ocean crust moves apart allowing magma to rise forming new ocean crust • The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans.

8. - Sea-Floor Spreading What Is Sea-Floor Spreading? • Sea-floor spreading occurs when • hot, less dense material below Earth’s crust rises toward the surface of the mid-ocean ridge • flows sideways carrying the carrying the seafloor away from the ridge in both directions • makes new ocean crust • Works like a conveyer belt • Older rock is found farther from the ridge

9. Growing an Ocean Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

10. Theory of Plate Tectonics Explains the formation, movement, and subduction of Earth’s plates. Claims that Earth’s plates are always in motion Plates move slowly at different rates in different directions

11. Structure of the Earth The Earth is made of 4 layers Inner Core Outer Core Mantle Crust

12. Crust Mostly solid rocky outer layer of Earth includes: Oceans crust: under the ocean & more dense Continental crust: surface of earth & less dense Earth’s crust & upper mantle are broken into large plates Together the crust and plates make up the lithosphere Lithosphere is the outermost solid, rocky surface of the Earth that floats on top of the asthenosphere Brittle, rigid, & has fault lines

13. Lithospheric Plates

14. Mantle Solid layer of hot rock Upper mantle melts rocks, forming a substance called magma which flows like a thick liquid The asthenosphere is the mechanically weak deforming region of the upper mantle that is ductile, plastic, and free-flowing Convection currents occur here due to uneven heating

15. Convection Currents in the Mantle • Convection currents can cause plates to move away from each other or towards each other • Convection currents: • hot less dense rock rises to the lithosphere & spreads out cooling & shrinking in volume • The cooler more dense rock sinks allowing the hot less dense rock to rise and take its place • As convection currents move the plastic rocks sideways large portions of the crust move called lithospheric plates

16. Compare & Contrast Lithosphere & Asthenosphere Using a double bubble

17. Plate Boundaries Movement of Earth plates are responsible for most major geological events and landforms Volcanoes, earthquakes, mountain formation Plate Boundaries are where edges of plates interact 3 Types of plate boundaries Divergent Plate Boundaries Convergent Plate Boundaries Transform Plate Boundaries

18. Plate Boundaries Different type of plate movement occurs along each type of boundary.

19. Divergent Plate Boundaries Forms when 2 plates move away from each other Two types: 2 oceanic 2 continental

20. Divergent Boundaries:2 ocean plates • Form undersea volcanic mountain ranges called mid-ocean ridges. • Ex. Mid-Atlantic Ridge

21. Divergent Boundaries:2 continental plates When two continental plates pull apart a rift valley forms Ex. Great Rift Valley in Africa

22. Convergent Plate Boundaries Boundaries that form when 2 plates collide or come together 3 Types Oceanic & Continental Two Oceanic Two Continental

23. Oceanic & Continental The denser oceanic plate is forced below the less dense continental plate The movement of one plate under another forms a subduction zone Oceanic plate melts as it subducts into the mantle forcing hot magma & gas up to the surface of the continent Forms a deep-ocean trench & a long chain of continental volcanic mountains Ex. : Mt. St. Helens

24. Two Oceanic Plates The less dense ocean plate is forced down into the mantle forming a deep ocean trench that sinks & melts Magma & gas push through the ocean floor forming a chain volcanoes If volcanoes become large enough it rises above sea level & makes a volcanic island arc Ex. Mariana Trench & Mariana Island Arc in the Western Pacific & Japanese islands

25. Volcanoes and Plate Boundaries Volcanic belts form along the boundaries of Earth’s plates.

26. Two Continental Plates First, the seafloor between the continents is forced below one of the continents Then, when the plates collide the continent crusts buckle, thicken, & rises up forming mountain ranges Compressional forces squeeze plates together causing Folding & Faulting Ex. Himalaya & Appalachian Mountains

27. Folding

28. Faulting

29. Transform Plate Boundaries 2 plates grind or slide past each other without creating or destroying the lithosphere Form Strike-slip faults Earthquakes occur at transform boundaries San Andreas Fault is an example North America & Pacific plates slide past each other in a N – S direction creating earthquakes

30. Earthquakes Faults are large cracks in the Earth’s crust where movement occurs At Strike-slip faults rocks on either side of the fault are under pressure & can get locked together When too much pressure builds up, the rocks suddenly slide past each other releasing the pressure The violent shaking of the Earth’s crust is known as an earthquake

31. New Madrid Fault