Objectives

1. Objectives Describe the geologic time scale.

2. By studying the characteristics of rocks and the fossils within them, geologists can interpret the environments in which the rocks were deposited, reconstruct Earth�s history, and possibly predict events or conditions in the future. The Geologic Time Scale

3. The Rock Record Geologists have divided the history of Earth into time units based upon the fossils contained within the rocks.

4. The Rock Record

5. Geologic Time The oldest division of time is at the bottom of the geologic time scale.

6. Geologic Time Precambrian Time, which makes up approximately 90 percent of geologic time, is divided into the Archean and Proterozoic Eons.

7. Geologic Time Plants and Animals Evolve

8. Geologic Time Periods of Geologic Time

9. Geologic Time Epochs of Geologic Time

10. Section Assessment 1. Match the following terms with their definitions. ___ eon ___ period ___ era ___ epoch

11. Section Assessment 2. How does the geologic time scale correspond with the rock record?

12. Section Assessment 3. Identify whether the following statements are true or false.

13. End of Section 1

14. Objectives Apply the principles for determining relative age to interpret rock sequences.

15. Relative-Age Dating of Rocks The principle of uniformitarianism states that the forces that continually change the surface features of Earth today have been occurring since Earth formed.

16. Principles for Determining Relative Age The concept of relative-age dating places the ages of rocks and the events that formed them in order, but without exact dates.

17. Principles for Determining Relative Age Geologic Principles

18. Principles for Determining Relative Age Geologic Principles

19. Principles for Determining Relative Age Inclusions

20. Other Means of Determining Relative Age The fact that Earth is constantly changing makes it difficult to find an undisturbed sequence of rock layers.

21. Other Means of Determining Relative Age The unconformity is called a disconformity when horizontal sedimentary rocks overlie horizontal sedimentary rocks.

22. Other Means of Determining Relative Age A different type of unconformity exists when sedimentary rocks overlie nonsedimentary rocks.

23. Other Means of Determining Relative Age An angular unconformity is created when horizontal sedimentary rocks are uplifted and tilted, are exposed to erosional processes, and deposition resumes.

24. Other Means of Determining Relative Age Correlation of Rock Strata

25. Section Assessment 1. Match the following terms with their definitions. ___ original horizontality ___ superposition ___ unconformity ___ correlation

26. Section Assessment 2. What is the principle of uniformitarianism?

27. Section Assessment 3. Identify whether the following statements are true or false.

28. End of Section 2

29. Objectives Explain the several different methods used by scientists to determine absolute age.

30. Absolute-Age Dating of Rocks Absolute-age dating enables scientists to determine the actual age of a rock, fossil, or other object using the decay rate of radioactive isotopes.

31. Absolute-Age Dating of Rocks Radioactive decay is the emission of radioactive particles and the resulting change into other elements over time.

32. Use of Radioactive Isotopes In a process called radiometric dating, scientists attempt to determine the ratio of parent nuclei to daughter nuclei within a given sample of a rock or fossil to determine its absolute age.

33. Use of Radioactive Isotopes Half-life is the length of time it takes for one-half of the original amount of an isotope to decay.

34. Use of Radioactive Isotopes Carbon-14

35. Other Ways to Determine Age Naturally occurring materials, such as trees, lake-bottom sediment, and volcanic ash can also be used to help geologists determine the age of an object or event.

36. Other Ways to Determine Age Tree Rings

37. Other Ways to Determine Age Seasonal Climatic Changes

38. Other Ways to Determine Age Distinctive Sediment Layers

39. Section Assessment 1. Match the following terms with their definitions. ___ half-life ___ dendrochronology ___ varve ___ key bed

40. Section Assessment 2. How old is an object of organic origin if it has 25 percent of carbon-14 remaining? Why?

41. Section Assessment 3. Why would rubidium-87 with a half-life of 48.6 billion years probably not be useful in dating an object that is 100 000 years old?

42. End of Section 3

43. Objectives Define fossil.

44. Remains of Organisms in the Rock Record Fossils are the evidence or remains of once-living plants or animals.

45. Types of Fossils Fossils with original preservation are the soft and hard parts of plant and animal remains that have not undergone any kind of change since the organisms� deaths.

46. Types of Fossils Altered Hard Parts

47. Types of Fossils Altered Hard Parts

48. Types of Fossils Index Fossils

49. Types of Fossils Molds and Casts

50. Types of Fossils Molds and Casts

51. Types of Fossils Indirect Evidence of Past Life

52. Why study fossils? The study of fossils allows scientists to interpret and describe Earth�s history.

53. Section Assessment 1. Match the following terms with their definitions. ___ original  preservation ___ altered hard part ___ permineralization ___ cast

54. Section Assessment 2. What conditions are necessary to allow original preservation?

55. Section Assessment 3. How might petroleum geologists use fossils?

56. End of Section 3

57. Chapter Resources Menu Study Guide Section 21.1 Section 21.2 Section 21.3 Section 21.4 Chapter Assessment Image Bank

58. Section 21.1 Main Ideas Geologists have separated Earth�s history into divisions based upon the fossil record.

59. Section 21.2 Main Ideas The principles of uniformitarianism, original horizontality, superposition, and cross-cutting relationships are used to interpret Earth�s rock record and, thus, to describe the planet�s history.

60. Section 21.3 Main Ideas Absolute-age dating measures the actual age of an object such as a mineral, rock, or fossil.

61. Section 21.4 Main Ideas The remains and evidence of plants and animals that once lived on Earth are called fossils.

62. 1. Which of the following is not an eon? a. Phanerozoic c. Cenozoic b. Proterozoic d. Archean Multiple Choice

63. 2. A gap in the rock record is known as a(n) ____. a. unconformity c. superposition b. correlation d. inclusion Multiple Choice

64. Multiple Choice 3. Approximately how old is a wood sample that has 3.2 percent of its C-14 remaining? a. 11 000 years c. 24 000 years b. 16 000 years d. 28 000 years

65. Multiple Choice 4. A change in populations as a result of environmental change is known as ____. a. permineralization c. altered hard parts b. fossilization d. evolution

66. Multiple Choice 5. On the geologic time scale, which division is defined by the life forms that were abundant or became extinct? a. period c. eon b. era d. epoch

67. Short Answer 6. What does the principle of superposition state?

68. Short Answer 7. What does the principle of cross-cutting relationships state?

69. True or False 8. Identify whether the following statements are true or false. ______ Fallout from a major volcanic eruption can form  a key bed. ______ Homo sapiens evolved in the past .01 M.Y.B.P. ______ Varves are direct evidence of past life-forms. ______ Dendrochronology is limited to the age of the  oldest living tree. ______ The first fish appeared in the Paleozoic Era. ______ All organisms contain carbon.

70. Chapter 21 Images

71. Chapter 21 Images

72. Chapter 21 Images

73. Help

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