1. Distinct properties define Earth’s three main layers: crust, mantle, and core. The crust is the rigid outer layer that makes up the continents and sea floors. The lithosphere is a region formed by the crust and the rigid outer layer of the mantle. The asthenosphere is the fluid-like layer of mantle beneath the lithosphere. Earth’s centre has two layers: a liquid outer core and a solid inner core. Structure of Earth 17.1 VOCABULARY crust mantle lithosphere asthenosphere core outer core inner core

2. Scientists obtain information about the structure of Earth through direct and indirect observations. Direct observations include analyzing rock directly from Earth’s interior. Structure of Earth 17.1 e.g. Sampling lava flows, to compare minerals in magma to other minerals in rock at or near the Earth’s surface e.g. Taking rock samples, collected from holes drilled into Earth during oil/mining exploration Continental rockOcean floor rock This sucks!

3. Scientists obtain information about the structure of Earth through direct and indirect observations. Indirect observations include measuring gravitational force differences around the globe to infer the density of material beneath Earth’s surface. Measuring Earth’s magnetic field Measuring the local strength of gravity Structure of Earth 17.1

4. The surface of Earth moves constantly. The lithosphere is divided into massive tectonic plates that are pushed and pulled over the asthenosphere. Continental drift theory argues that the continents have moved slowly since Earth formed. Fossil and geological evidence support the continental drift theory. At one time, the continents formed Pangaea, a single huge landmass. Evidence of a Dynamic Earth 17.2 VOCABULARY tectonic plate continental drift theory paleoglaciation

5. Continental Drift Theory  Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent. Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses. 17.2

6. Breakup of Pangaea 17.2

7. Continental Drift Theory  Evidence The Continental Puzzle (see previous slides) Matching Fossils - Fossil evidence for continental drift includes several similar fossils of the same organisms found on different landmasses. 17.2

8. Continental Drift Theory  Evidence Rock Types and Structures - Rock evidence for continental exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean. 17.2

9. Continental Drift Theory  Evidence Ancient Glacial Evidence - Glaciers scratch grooves into Earth’s crust as they move, indicating their direction of movement. Groove patterns match up with Wegener’s theory of how Pangaea broke apart. 17.2

10. Glacier Evidence 17.2

11. Continental Drift Theory  The idea of continental drift was met with a lot of opposition. The main problems with it were : The age of the Earth would have to be billions of years, not just thousands of years. At the time, scientists believed it was only 6000 to 400 million years old. More importantly, Wegner could not explain HOW the plates moved. 17.2

12. Sea-floor spreading occurs at mid-ocean ridges and subduction occurs at deep ocean trenches. Heat within Earth creates convection currents in the mantle that help move the plates. Radioactive dating of core samples confirmed evidence that the sea floor is older the further it is from the ridges. Magnetic striping patterns in sea floor rock are similar on both sides of an oceanic ridge, suggesting new ocean floor is being created at the ridge. New Evidence of a Dynamic Earth 17.3 VOCABULARY mid-ocean ridge sea-floor spreading ocean trench

13. During World War II, Henry Hess was in charge of a submarine that discovered mid-ocean ridges. A mid-ocean ridge is a massive undersea mountain range that runs along the bottom of the ocean. Since this initial discovery, a total length of 75,000 km of mid-ocean ridges has been discovered. New Evidence of a Dynamic Earth 17.3

14. Hess proposed a process called sea-floor spreading to explain why the sea floor was widening at mid-ocean ridges. Molten magma from the Earth’s core rises and fills the ridges. Future work suggested the sea floor was cycled back into the Earth to create ocean trenches. New Evidence of a Dynamic Earth 17.3

15. Radioactive dating (using half-life!) suggests age of the rock further from the mid-ocean ridge is older. Magnetic lava that has cooled to form rock has taken on the alignment of the magnetic field of the Earth. Bands that show opposite magnetization along the ocean floor suggest the rock has formed at different geological times. New Evidence of a Dynamic Earth 17.3

16. Polarity of the Ocean Crust 17.3

17. New Evidence of a Dynamic Earth 17.3 Some Videos: Lava sampling = http://www.youtube.com/watch?v=rxJeY4C6SL4http://www.youtube.com/watch?v=rxJeY4C6SL4 Magnetic evidence = http://www.youtube.com/watch?v=BCzCmldiaWQhttp://www.youtube.com/watch?v=BCzCmldiaWQ Most incredible volcano expedition EVER! = http://www.youtube.com/watch?v=egEGaBXG3Kg http://www.youtube.com/watch?v=egEGaBXG3Kg

18. All of this evidence provided a convincing case that sea-floor spreading is a real phenomenon – the Earth’s lithosphere is in motion! New Evidence of a Dynamic Earth 17.3

19. The theory of plate tectonics states that the lithosphere is divided into 12 large sections (plates) and about 20 smaller ones. These plates ‘float’ on the more dense, fluid-like asthenosphere Theory of Plate Tectonics 17.4 VOCABULARY theory of plate tectonics divergent boundary rift valley convergent boundary subduction zone oceanic–oceanic convergent boundary oceanic–continental convergent boundary continental–continental convergent boundary transform boundary strike–slip fault

20. Three types of boundaries exist where tectonic plates meet. These create Earth’s geological features and events. Ridges, rifts, volcanoes and earthquakes are created at divergent boundaries, where plates are moving away from each other. At convergent boundaries (where plates move toward each other), we find mountains, trenches, subduction zones, volcanoes, and earthquakes, depending on the types of plates involved. Earthquakes and strike-slip faults are created along transform boundaries, where plates move past each other in opposite directions. Theory of Plate Tectonics 17.4 VOCABULARY theory of plate tectonics divergent boundary rift valley convergent boundary subduction zone oceanic–oceanic convergent boundary oceanic–continental convergent boundary continental–continental convergent boundary transform boundary strike–slip fault

21. Three Types of Plate Boundaries 17.4 Theory of Plate Tectonics

22.  Continental Rifts When spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift. Divergent Boundaries 17.4 East African Rift Valley

23.  A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate. Denser oceanic slab sinks into the asthenosphere.  Oceanic-Continental Pockets of magma develop and rise. Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent. Examples include the Andes, Cascades, and the Sierra Nevadas. Convergent Boundaries 17.4 review

24. Oceanic-Continental Convergent Boundary 17.4 Convergent Boundaries

25. Two oceanic slabs converge and one descends beneath the other.  Oceanic-Oceanic This kind of boundary often forms volcanoes on the ocean floor. Volcanic island arcs form as volcanoes emerge from the sea. Examples include the Aleutian, Mariana, and Tonga islands. Convergent Boundaries 17.4

26. Oceanic-Oceanic Convergent Boundary 17.4 Convergent Boundaries

27. When subducting plates contain continental material, two continents collide.  Continental-Continental This kind of boundary can produce new mountain ranges, such as the Himalayas. Convergent Boundaries 17.4

28. Convergent Boundaries 17.4 Continental-Continental Convergent Boundary

29. Convergent Boundaries 17.4 ‘Collision of India and Asia ’

30.  At a transform fault boundary, plates grind past each other without ‘destroying’ the lithosphere.  Transform faults When the faults ‘overcome’ the friction holding them in place, the ‘slip’ causes earthquakes Transform Boundaries 17.4

31. Transform Fault Boundaries 17.4 Transform Boundaries

32. Scientists now believe that three forces work together to move the tectonic plates: 1. mantle convection 2. ridge push 3. slab pull Causes and Effects of Plate Movement 18.1 VOCABULARY mantle convection ridge push slab pull Forces at plate boundaries produce landscape features such as mountains, trenches, and island arches.

33. Uplifted mountains, volcanic belts, and island arcs are found parallel to convergent boundaries. Ocean trenches lie along convergent boundaries. Mid-ocean ridges and rift valleys mark divergent boundaries. Causes and Effects of Plate Movement 18.1 VOCABULARY mantle convection ridge push slab pull

34. 18.1 Causes and Effects of Plate Movement  Scientists believe tectonic plates are moved by three forces: o Mantle convection is the idea that there is a treadmill-like current in the asthenosphere that moves the crust that sits above it. (hot magma rises in one area and cool magma sinks in another) Convective flow is the motion of matter resulting from changes in temperature.

35. Causes and Effects of Plate Movement Convection causes Ridge Push and Slab Pull... Ridge Push Slab Pull Ridge Push Slab Pull Ridge Push 18.1  Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement.

36. 18.1 Causes and Effects of Plate Movement  Scientists believe tectonic plates are moved by three forces: o Ridge Push is the idea that the hot magma pushing up the mid-ocean ridges is also pushing the ocean plates apart.

37. 18.1 Causes and Effects of Plate Movement  Scientists believe tectonic plates are moved by three forces: o Slab Pull is when one plate slides underneath the other. The subduction zone causes the bottom plate to be pushed back into the mantle and this pulls the plate away from the mid- ocean ridge.

38. 18.1 Causes and Effects of Plate Movement  Mountains form at convergent boundaries. o Ocean – continent boundary causes mountains to form along the coast. These often push land that was once underwater up high causing ocean fossils to be found in the mountains.

39. 18.1 Causes and Effects of Plate Movement  Mountains form at convergent boundaries. o Continent – continent boundary causes mountains to form from the uplifting of the two continent edges. This can also cause former coast lines and marine fossils to be found in the mountains.

40. 18.1 Causes and Effects of Plate Movement Rifts form at divergent boundaries. If this happens on land a rift valley forms. Often volcanoes also form along these rifts since the crust is thinner.

41. 18.1 Causes and Effects of Plate Movement  Trenches can form at a convergent boundary. o They occur where one plate is subducted under the other. If there are mountain chains along a coast then you know that a few hundred kilometers out into the ocean that there must be a trench.

42. 18.1 Causes and Effects of Plate Movement  Trenches can form at a convergent boundary. o When trenches form at oceanic-oceanic convergent boundaries, a deep ocean trench is also formed o The Mariana trench is Earth’s deepest trench, still sinking, and is ~ 11 km below the surface of the ocean!

43. Volcanoes are produced over lithosphere cracks and mantle hot spots. Hot spots are rising plumes of hot mantle magma. As tectonic plates move over the hot spot, a chain of progressively younger volcanoes is formed opposite to the direction of plate movement. Volcanic island chains and volcanic belts are created on the overriding plate, parallel to the direction of the moving oceanic plate. Geological Events 18.2 VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave

44. Earthquakes result when tectonic forces overcome the friction between plates. Earthquakes are categorized based on how far beneath the surface the focus is located. The sudden movement of the lithosphere during an earthquake sends seismic waves (vibrations) through Earth. Primary and secondary body waves travel through Earth, starting at the focus, the site of the earthquake within Earth. Surface waves travel along the outside of Earth. They cause the most destruction. Geological Events 18.2 VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave

45.  A Volcano marks a spot where there is a crack in the lithosphere. a.They can form at mid-ocean ridges where plates are being pulled apart, and magma rises up. Geological Events 18.2

46.  A Volcano marks a spot where there is a crack in the lithosphere. b. They can also form about 200 km from a trench, when trapped water becomes steam and melts through the crust. This forms volcano belts on continents and volcanic island arcs in the ocean. Geological Events 18.2

47.  A Volcano marks a spot where there is a crack in the lithosphere. b. They can also form about 200 km from a trench, when trapped water becomes steam and melts through the crust. This forms volcano belts on continents and volcanic island arcs in the ocean. Geological Events 18.2

48.  A Volcano marks a spot where there is a crack in the lithosphere. c. They can form above a hot spot in the mantle, caused by heated concentrations of radioactive substances near the Earth’s core, causing hot columns of rising mantle that melt through the crust. Geological Events 18.2

49.  Hot Spots A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands. Hot spot evidence supports that the plates move over the Earth’s surface. 18.2 Geological Events

50. 18.2 Geological Events Hot Spot

51.  Earthquakes happen when two tectonic plates move past each other. The plates do not have smooth edges so there is tremendous friction that keeps them from sliding...until enough pressure builds up, and then the plates move suddenly. This sudden movement is what we call an earthquake.  The boundary where the two plates move past each other is called a fault. Geological Events 18.2

52.  The location of the earthquake is called the focus. The focus can be deep in the earth or relatively shallow down. It depends which part of the two plates slide past each other.  The epicenter is the spot above the focus, on the surface of the Earth. Earthquakes are categorized according to the depth of their focus. Geological Events 18.2

53.  Plotting epicenters on a map (this data: 1980-1996) clearly outline some of the plate boundaries. Geological Events 18.2

54.  Earthquakes travel through the Earth in wave form. These are called body waves and there are two kinds: a.Primary waves (P-waves) are waves that travel parallel to the direction of the wave. They are a ‘compression’ wave. They are like pulling on a spring and letting the end go. It stretches and compresses. They can travel through all parts of the Earth. b.Secondary waves (S-waves) are waves that travel sideways (shear) to the direction of the wave. They are like a slithery snake. They can only travel through the mantle and the crust. They cannot travel through the core. Geological Events 18.2

55.  The most destructive kind of earthquake wave is called a surface wave. They travel along the surface of the crust like a wave on the ocean. They are what destroy buildings, bridges, etc.  Scientists use instruments called seismographs to measure the strength of earthquakes. They use the Richter scale. Each increase of 1 on the scale means that the earthquake is 10 times as strong. An earthquake of 5 is 10 times stronger than a 4. Geological Events 18.2