2. The Four Layers of the Earth

3. The Two Cores Inner Core –Solid iron and nickel –Very high density –Temperatures are high enough in the inner core to melt the iron and nickel, but the pressure from the layers above it prevent this from happening Outer Core –Liquid iron and nickel

4. Mantle Largest Earth layer Largest Earth layer Made of mostly solid rock, with the exception of the upper mantle Made of mostly solid rock, with the exception of the upper mantle The upper mantle, known as the Asthenosphere, is considered a solid but acts more like a plastic (almost like silly putty) The upper mantle, known as the Asthenosphere, is considered a solid but acts more like a plastic (almost like silly putty)

5. Crust Outermost layer Outermost layer Thinnest layer Thinnest layer Greater than 60 kilometers thick beneath the continents Greater than 60 kilometers thick beneath the continents Less than 5 kilometers thick beneath the oceans Less than 5 kilometers thick beneath the oceans All of our natural resources come from the Earth’s crust All of our natural resources come from the Earth’s crust

6. Our Crust is extremely thin

7. Continental Crust vs. Oceanic Crust Continental Crust –Crust beneath the Earth’s continents –Less dense and thicker than oceanic crust –Composed of Granite (less dense because it is high in Silicon & Oxygen) Oceanic Crust –Crust beneath the Earth’s oceans –More dense and thinner than continental crust –Composed of Basalt (dense because it is high in Iron & Magnesium)

8. Two types of crust

9. The Idea of Continental Drift

10. Continental Drift Accurate maps of the world were not developed until the 1800’s A man named Alfred Wegener believed the fit of the continents was no coincidence In 1912, Wegener proposed a theory called continental drift

11. Continental Drift In his theory he proposed that the continents were at one time connected together as one large landmass that he called Pangaea. (Pangaea means all land) Wegener thought that this huge landmass broke apart about 200 million years ago and the continents drifted to their present positions There was one big problem with Wegener’s idea – He could not explain HOW any of this happened!

13. Wegener’s 3 Big Pieces of Evidence Wegener had 3 pieces of evidence for his idea of continental drift: –Fossil Evidence –Climate Evidence –Rock Evidence

14. Fossil Evidence Similar fossils have been found on different continents Mesosaurus – swimming fresh water reptile Wegener found Mesosaurus fossil remains in South America & Africa

15. More Fossil Evidence Glossopteris – warm weather fossil fern Wegener found Glossopteris fossil remains in Africa, Australia, India, South America, and Antarctica

16. Chart showing all Wegner’s Fossil Clues

17. Climate Evidence Fossils of warm weather plants were found on an island in the Arctic Ocean Glacial deposits and grooved bedrock were found in southern areas of South America, Africa, India, and Australia

18. Rock Evidence Similar rock structures have been found on different continents Parts of the Appalachian Mountains of the eastern United States are similar to the mountains in Greenland and western Europe Similar rock structures were found in South America and Western Africa

19. Rock and Climate Evidence

20. What was still the big problem with Wegener’s idea of Continental Drift? He could not explain HOW the continents moved to where they are today!

21. Sea Floor Spreading The development of echo sounding in the 1950’s helped scientists make the first accurate maps of the ocean floor While mapping the ocean floor…..we found a startling discovery! There is a mid-ocean ridge system that forms an underwater mountain range that extends through the center of many of the Earth’s oceans

22. The Mid- Atlantic Ridge

23. So what had caused these mid- ocean ridge systems? A man named Harry Hess proposed a theory known as sea floor spreading

24. His theory had three parts: 1. Hot, less dense magma in the mantle is forced upward to the surface at mid-ocean ridges 2. Some of the magma then cools and hardens forming the mid-ocean ridge system and pushing the plates apart 3. The rest of the magma, flows sideways and carries the seafloor away horizontally from the ridge in both directions

25. Evidence for Sea Floor Spreading

26. Age Evidence  In 1968, scientists set out on the Glomar Challenger Deep Sea Drilling Ship to study the age of the ocean floor  They found that the oldest rocks on the sea floor were only 160 million years old (continental rocks found to be 4 billion yrs.)  The youngest rocks were located at the mid- ocean ridges and the rocks got older as you move out from the ridge

27. Magnetic Evidence Iron minerals in rocks like basalt, act like tiny compass needles and point toward magnetic north Scientists found that Earth’s magnetic field had reversed itself many times The magnetic alignment is shown in a pattern of parallel strips on either side of the mid-ocean ridge This discovery proved that sea floor spreading was happening!

28. Age and Magnetic Evidence http://earthguide.ucsd.edu/eoc/teachers/t_tect onics/p_paleomag.html http://earthguide.ucsd.edu/eoc/teachers/t_tect onics/p_paleomag.html

29. The Cause of Plate Tectonics (“Wegner’s How”) Convection Currents which exist in Earth’s mantle are the cause of the plate movements Density differences cause hot plastic-like rock of the Asthenosphere to be forced upward When this rock reaches the lithosphere, it moves horizontally carrying the plates along with it As the rock moves up closer to the surface, its temperature cools and it becomes more dense sinking back into the mantle and taking some of the overlying crust with it

30. Cause of Plate Tectonics

31. Types of Plate Boundaries

32. An Introduction Plate Tectonics – theory that Earth’s crust and upper mantle are broken into plates that move around on the Asthenosphere Asthenosphere – the plastic-like layer in the upper mantle Lithosphere – the outer shell of the Earth consisting of the crust and uppermost portion of the mantle. The lithosphere is broken into many plates. The less dense lithospheric plates float on the Asthenosphere.

33. 3 Types of Plate Boundaries: 1. Divergent 2. Convergent 3. Transform

34. Divergent Boundaries a boundary between two plates that are moving away from each other new ocean crust is formed at divergent plate boundaries

35. Locations of divergent boundaries: 1. The Mid-Atlantic Ridge (Atlantic Ocean) 2. The Great Rift Valley (eastern Africa)

36. This is a photo of a friend of mine that took a trip to Iceland. She is diving in between the North American Plate and Eurasian Plate. This is an example of a divergent plate boundary. North American Plate Eurasian Plate

37. Convergent Boundary a boundary between two plates moving toward each other There are three types of convergent boundaries Continent/OceanicOcean/OceanContinent/Continent

38. Oceanic-Continental Plate Collision

39. Ocean plate is more dense therefore sinks under continental plate and crust is melted into magma (this is called a subduction zone) Trenches form (V-shaped valleys, deepest parts of the ocean floor) Magma rises to form volcanic mountains

40. Locations of Oceanic- Continental Plate Collision 1. Andes Mountains in South America 2. Cascade Range in Northwestern USA

41. Oceanic-Oceanic Plate Collision

42. One ocean plate is pulled beneath the other (subduction zone) Trenches form Magma rises to form volcanic islands

43. Locations of Oceanic-Oceanic Plate Collision: 1. Japanese Islands 2. Aleutian Islands

44. Continent-Continent Plate Collision

45. Continental crust is not dense enough to sink (NO SUBDUCTION) The two plates crumple and form folded mountains (no volcanoes)

46. Locations of Continental- Continental Plate Collision: 1. Himalaya Mountains 2. Appalachian Mountains

47. Transform Fault Boundary (also called Sliding Boundaries)  A boundary in which two plates slide past each other horizontally  This occurs when the plates are moving in opposite directions or the same direction but at different rates

48. Transform Fault Boundary Faults and earthquakes occur here

49. Locations of Transform Fault Boundaries: San Andreas Fault (California)

50. Plate Boundaries