Unit 4: Earth Science

1. Unit 4: Earth Science Chapter 12: Earth’s Internal Processes

2. UNIT 4: Chapter 26: Earth’s Internal Processes I. Evolution of Earth’s Crust A. Continental Drift 1. Early 19th century there was no single theory of how Earth’s processes interrelated.

3. 2. In 1915, Alfred Wegener proposed hypothesis that suggested Earth’s continents once were part of large super-continent a. Called it Pangea b. Broke apart into pieces 200 million years ago

4. c. Pieces drifted over surface of Earth like rafts on water d. Idea originally met with great resistance (unable to identify force necessary)

5. 3. Matching Continents- If use your imagination you can see how pieces “fit together” a. Coastline of northwestern Africa fits with eastern United States b. South America and southern tip of Africa fit nicely together

6. c. Wegener argued you could match up rock types, fossils, erosion features, and mountain ranges d. Years later, oceanographers were able to show, using sonar, edges of continental shelves matched

7. 4. Matching Fossils- used fossils of large land animals that precededdinosaurs

8. 5. Matching Rocks and Mountains- a. Wegener showed that mountain ranges to be one mountain range originally b. Also showed they shared unique rocks and minerals

9. B. Seafloor Spreading Hypothesis 1. After World War II, Dr. Harry Hess used sonar to detect and map the seafloor

10. a. Detected that a mid-ocean ridge system (MOR) was continuous and wrapped around the Earth b. Proposed hypothesis of seafloor spreading or divergence

11. c. Proposed that magma from the Earth’s mantle is forced upwards because of its low density d. This caused the crust to crack (fault) and move apart

12. e. Faulting causes two mountain ranges with a down-dropped rift valley between f. Continuous process allows new rock to form as magma fills in from below

13. 2. Ages of Sediment and Rocks a. In early 1960’s massive programs for drilling into the seafloor began b. Discovered that continental rocks were billions of years old and seafloor rocks less than 200 million years old

14. c. Concluded that rocks of oceanic crust increase in age as their location extends from MOR, and at MOR they are new

15. 3. Magnetic Polarity of Rocks a. Discovered that Earth’s magnetic field repeatedly reverses itself over time b. Discovered bands of reversed polarity in seafloor rocks with polarity of Earth at time they formed

16. C. Theory of Plate Tectonics 1. Originated in the 1960’s 2. Identified about a dozenmajor plates and minor ones

17. 3. Plates composed of a rigid layer of uppermost mantle and a layer of either oceanic or continental crust above 4. Some only oceanic crust, and some combination oceanic and continental

18. 5. Three main kinds of plate motions   a. Move together b. Move apart c. slide past one another

19. 6. Divergent Plate Boundaries a. Occurs at MOR when magma rises along faulted rift valley, spreads, cools to form new oceanic crust b. Resulted in production of ocean basins

20. 7. Convergent Plate Boundaries a. Occurs where plates collide

21. b. Subduction- oceanic slab bends undercontinental slap Conduction zone

22. c. Heat along subduction zone partially melts rockand produces magma which rises towards surface d. Magma feeds volcanic arc that parallels this zone Volcanic Arc

23. e. Region of collision also has a deep-sea trench that parallels the zone f. Convergent plate boundaries also exist between two slabs of oceanic lithosphere

24. 1). Magma erupted here produces chains of volcanic island arcs 2). As plates converge, stress builds, which could be released as tsunami-causing earthquakes

25. g. Along some convergent plates, two slabs of low density collide and buckle upward forming folded mountains

26. 8. Transform Plate Boundaries a. Some boundaries among plates exist as large faults, or cracks b. Mostly horizontal motion takes place c. Important when cut perpendicular to MOR. They allow movement away from ridge crests to occur

27. D. What drives the plates? 1. Driven by combination of forces a. Ridge push at the MOR b. Plate pull where subducts back into Earth (gravity helps) c. Friction between a plate and the mantle material below the plate

28. 2. Thermal Energy-Internal convection of mantle material is the driving force for all mechanisms of plate motion a. Comes from decay of radioactive elements in Earth

29. b. Increased temperature due to pressure and frictional heating

30. c. Conversion of secondary earthquake waves in outer core another source of energy

31. II. Earthquakes A. Global Earthquake Distribution

32. 1. Earthquakes are not distributed randomly, but occur in well-defined zones a. Zones coincide with edges of plates

33. b. Seismic data from earthquakes helped to decipher structure of ocean floor

34. 2. Depth of Focus a. Transform faulting creates narrow band of numerous, shallow earthquakes b. Convergent boundaries have broad zone of earthquakes

35. B. Causes of Earthquakes 1. Earthquake- any seismic vibration of Earth caused by the rapid release of energy

36. 2. Deformation a. Earth’s crust composed of rigid, rocky material b. When stress applied to brittle material it shows little sign of strain (deformation) until it suddenly breaks

37. c. Stress can be of 4 types 1). Compressive stress- mass is squeezed or shortened 2). Tension stress- mass is stretched or lengthened 3). Shear stress- different parts of mass are moved in opposite direction along a plane 4). Tension stress- mass is subject to twisting

38. 3. Elastic Deformation- when material deforms as stress is applied, but snaps back to its original shape when stress removed

39. 4. Energy Release- strain energy builds up along cracks in Earth’s crust in response to stress

40. fault- crack along which movement has taken place • b. Elastic rebound- sudden energy release that goes with fault movement. Causesearthquakes

41. C. Earthquake Waves 1. Earthquake waves travel out in all directions a. Focus- point of origin b. Epicenter- Point on Earth’s surface directly above the focus

42. 2. Earthquake waves can be sorted into two major types a. Body Waves- Travel through Earth

43. b. Surface Waves- travel across Earth’s surface

44. 3. Body Waves a. Primary wave (P-waves)- push-pull motion 1). Matter bumps into each other and transmits energy like sound wave 2). Travel through all kinds of matter

45. b. Secondary wave (S-waves) 1). Travel more slowly 2). Movement of particles perpendicular to direction wave

46. 3). Lag time between P-wave and S-waves used to locate epicenter 4). Only travels through solids

47. 4. Surface Waves a. Move in more complex manner b. Cause rolling motion like ocean wave c. Exhibit rolling motion and side-to-side motion

48. D. Earthquake Measurement 1. Two measurement schemes have been used a. Modified Mercalli intensity scale- ranks earthquakes in a range from I-XII, XII being the worst. Based eyewitness observations

49. b. Richter Magnitude scale- uses amplitude of thelargest earthquake wave giving measure of energy release 1). Called Richter Scale for short 2). Measurements made with a seismograph Ancient Chinese seismograph

50. 2. Levels of destruction is extremely variable a. Poor building materials are largest contributor b. Some damage is secondary- caused by landslides, fires, and tsunamis