historical geology exam 1

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Historical Geology Exam 1

• you may use a ruler and a calculator (of your choosing) • you will need colored pencils • the exam is closed book • unlimited time • no scantron necessary – put all answers on these pages

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The Geologic Time Scale….

Using the graph paper on the next page,

1. draw the Geologic Time Scale – to-scale…

2. In dark blue - label the Eons, Eras and Periods

3. In dark blue - label the Cenozoic Epochs

4. In green - label the dates a. at the beginning and end of the time scale b. at the beginning of each Eon and Era

5. In red - print all major events and “Ages of….”

6. In regular pencil - print brief descriptions of the life and conditions in each Eon

and Era. – lists are sufficient; do not use complete sentences (you won’t have room)

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The Geologic Time Scale

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Radiometric Dating

Use the graph paper on the following page

7. Using your ruler, draw a general radiometric decay graph 8. Label both axes appropriately (both words and numbers) 9. Graph the points for at least 8 half-lives 10. Don’t forget to graph the starting point at t1/2 = 0

11. Using your graph, estimate how much parent material is left after XX half-lives.

12. Again, using your graph, how many half-lives must pass for XX% of the material to decay to the daughter element?

List 4 common radiometric parent-daughter elements and estimate their half-lives. Radiometric Parent-Daughter Elements Half-Lives

13. C14 decays to ? 14.

15. U238 decays to ? 16.

17. Rb87 decays to ? 18.

19. K40 decays to ? 20.

21. Using your radiometric graph, and your half-lives listed above, estimate the age of a sample with XX% K40 left.

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Radiometric Dating

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22. What is the oldest sample that can be reasonably dated with radiocarbon?

23. Why can’t trilobite fossils be dated with radiocarbon?

24. What type of rock are most fossils found in?

25. What type of rock generally provides the most accurate radiometric dating results?

26. Which of the following should you use to get the best results for radiometric

dating of an Anasazi pottery shard?

27. Which of the following has a half-life that is “convenient” for estimating the age of the Earth’s formation?

28. What are the ages of the oldest Earth rocks?

29. Radiometric age-dating indicates that the earth is

30. Even though no rocks have ever been found from the initial solidification of the

earth’s crust, what is used to estimate is the age of the early earth?

31. What group of fossils is the oldest known “find” of metazoans (multi-cellular organisms)?

32. The group of fossils above included

33. Which of the following fossil assemblages indicate Paleozoic rocks?

34. Giant ammonites fossils are most commonly found in rocks of what age?

35. The earliest “bird-like” fossils with definite feathers are found in rocks of what age?

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36. The fossil record indicates that whales, dolphins, sea lions and all other sea

mammals evolved from

37. Which of the following are “living fossils”?

38. What is the common measurement error in radiocarbon dating? (give your answer in +/- years)

39. What is the common measurement error in K-Ar dating?

(give your answer in +/- years)

40. What is the common measurement error in Rb-Sr dating? (give your answer in +/- years)

41. Explain how a single rock layer can have trilobite fossils, ammonites and dolphin vertebrate in it?

42. Three samples are taken from the same rock layer. One sample yields a radiometric age of 3.7 billion years, the second sample yields a radiometric age of 2.5 million years and the third sample yields an age of 150 million years. How is this possible?

43. A certain sandstone layer is still in its original stratigraphic orientation (has not been tilted by plate textonics). Biostratigraphic dating indicates this sandstone layer is progressively younger as one traverses it laterally to the east. Explain how this can be true.

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44. List and briefly explain how geologic processes can “contaminate” (or produce false) radiometric age-dating results.

45. Explain cladograms. Make up an example cladogram and explain all parts of your diagram.

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46. Write a general equation which describes the fact that radiometric elements decay

such that ½ is left after one half life ¼ is left after two half lives

81 is left after three half lives 16

1 is left after four half lives 32

1 is left after five half lives etc……

Define all of your terms and/or variables.

47. Using your general equation above, what fraction of parent material is left after XX half lives? You may use your calculator but show all of your work and show what you plug where in your equation(s).

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48. Solve (or rework) your general half-life equation so that it is a general equation

which calculates the age of the sample from the fraction of parent material remaining. You may use log base 2 or log base e. Define all of your terms and/or variables.

49. Using your general age equation, calculate the age of a sample where XX% of the K40

parent material remains. 50. Compare your answer above to the your answer for question 21.

Which answer is more accurate? Why?

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For the following questions, use the Powerpoint Slide Show HistGeolExam. For each of the slides, identify the organism or fossil from the list provided below.

abalone

ammonite

archeopteryx

barnacles

belemnite

brachiopod

bryzoans

coccolithophores

conodont

diatoms

flat worms

foraminifera

graptolite

radioloarians

rugose coral

sand dollars

scallops

sea pen

sea urchins

stalked crinoid

stromatolites

trilobites

51. _____________________________

52. _____________________________

53. _____________________________

54. _____________________________

55. _____________________________

56. _____________________________

57. _____________________________

58. _____________________________

59. _____________________________

60. _____________________________

61. _____________________________

62. _____________________________

63. _____________________________

64. _____________________________

65. _____________________________

66. _____________________________

67. _____________________________

68. _____________________________

69. _____________________________

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The following questions refer to the last slide # 70.

70. Identify this group of organisms. ____________________

71. How old are they? _____________

72. Where were these fossils found? _____________

73. What is the significance of this group of organisms?

74. List the organisms in this group of fossils.

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75. Explain 2 ways that the age of the Earth can be determined.

76. What minerals are the most commonly tested for radiometric dating?

historical geology exam 1

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