1. The document discusses principles of geology including uniformitarianism and relative dating techniques like the laws of superposition, original horizontality, inclusion, and cross-cutting relationships that allow geologists to interpret past geological events and order the formation of rock layers. 2. It also describes how radioactive dating methods using elements like carbon-14, uranium-238, and potassium-argon have enabled geologists to assign absolute ages to rocks and develop a geologic timescale. 3. Key principles discussed include radioactive decay and half-life, which allow the calculation of sample ages by measuring current isotope ratios.

1. Interpreting Geologic History

2. THE PRINCIPLE OF UNIFORMITY: Geologists can infer events of the past by Looking at features of rocks and rock outcrops

3. Uniformitarianism (Principle of states that the forces that acted upon the ___________ crust… Uniformity) Earth’s

4. in the __________ are the same as those that are ____________ today. past active ** THE KEY TO THE PAST IS THE PRESENT**

5. Relative Dating Techniques

6. 5 Basic Laws: 1. Law of Original Horizontality 2. Law of Superposition 3. Law of Inclusions 4. Law of Cross-Cutting Relationships 5. Law of Original Lateral Continuity

7. Law of Original Horizontality Strata is originally deposited in flat horizontal layers because sedimentary particles settle from air and water under the influence of gravity

8. Law of Original Horizontality If strata are ___________, then they must have suffered some kind of disturbance after they were deposited. Grand Canyon Western Iran Steeply Inclined

9. THE LAW OF SUPERPOSITION: the principle that the _________ layers in a sequence of rock strata must have been deposited __________ the layers above, unless the rock strata have been ___________ or___________ bottom before disturbed uplifted

10. The _______ rocks are found at the bottom. Geologists can date the _________ ages of the strata from ________ to __________ older relative oldest youngest

11. oldest youngest

12. Law of Superposition Therefore the order of deposition is from the bottom upward.

13. Law of Inclusions A rock must first exist in order to be weathered, deposited and cemented as a _____ in another rock. Therefore… clast

14. If rock is composed of _____________, the rock fragments must be ___________ than the rock in which they are found. fragments older

15. Law of Inclusions Which is older the Granite or the Sandstone? In figure A? In figure B? Sandstone is older Granite is older

16. The law of inclusions also applies to fossils preserved in the bedrock.

17. _________ are any naturally preserved remains or impressions of living things. Fossils

26. They are found in _______________ because _____________________ ____________ Sedimentary rock Heat & pressure in igneous and metamorphic rock destroys them

27. FOSSILS GIVE US INFORMATION ABOUT THE ANCIENT ENVIRONMENT AND CLIMATE

28. Law of Cross-Cutting Relationships Any __________ or ______, must be younger than all rocks through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault. Igneous rock fault

29. In general rock is always_________ than the process that changed it. older

30. Some Processes Include: folds faults tilts intrusions extrusions

31. Sedimentary layers (the law of original horizontality)

32. Sedimentary layers

33. Sedimentary layers

34. Sedimentary layers

35. Sedimentary layers

36. The fault came after the rock was formed

37. Sedimentary layers The tilt came after the the rock was formed

38. The extrusion came after the rock was formed 1 2 3 4 5 Contact metamorphism

39. 1 2 3 4 5 6 The extrusion came after the lower layers were formed but…. Before the top layer

40. 1 2 3 4 5 This intrusion came after all the layers

42. These changes can lead to exceptions to the Law of Superposition: a.An __________ is an igneous rock that formed from lava on the surface of the crust. extrusion

43. An __________ must be younger than the strata below it, but ________ than any layers above. extrusion older

44. b. __________ are created when molten rock (________) is injected into older rock layers in the crust. intrusions magma

45. _____________ are _____________ than all the rock layers in contact with them. Intrusions younger

46. c. _______ are bends in the rock strata. ________ can overturn rock strata so that ________ rock lies on top of _________ rock. Folds folding older younger

49. d. _______ are cracks in rock strata. _______ produce offset layers. Faults Faults

50. d. _______ are cracks in rock strata. _______ produce offset layers. Faults Faults

51. Rock strata must be ________ than the process that changed it. older

52. _________, ________ and ________ ___________ are features created after rock or sediment has been deposited. cracks veins natural cement

54. Law of Original Lateral Continuity . When sediment is dumped by an agent of erosion, strata extends from the source until it gradually thins to zero, or until it reaches the edges of the basin of __________. deposition

55. Law of Original Lateral Continuity

56. Law of Original Lateral Continuity This concept enables us to correlate outcrops of strata that has been dissected by processes of ________. erosion

57. CORRELATION OF ROCK STRATA: Correlation is Matching similar rock strata at different locations to see if they formed at the same time

58. Ways to correlate rock formations: “ Walking the outcrop” is done by Walking from end to end

59. This is correlation by continuity

60. You can match the rock strata in one location with rock strata in more distant locations by Comparing , c o l o r texture composition sequence of layers

61. Time correlation compares ____________ contained in the rock strata index fossils 1 2 3 4 4 5 6 3

62. The best index fossils: a. _________________ b. _________________ Exist for a brief period of time are widespread

63. Which fossil would make the best index fossil? Found in only 1 layer (short lived) Found in all samples (widespread)

64. Another way of correlating layers by time is through ___________________ Volcanic ash falls

65. These ash falls are very ________ events. A single layer of ______ can be found over a large area, this allows geologists to make a__________________ from one location to another at the position of a common ash fall. brief ash time correlation

66. GEOLOGIC TIME SCALE: A. Geologists noticed that rock _________ can be identified by the fossils they contained. formations

67. They also found that certain __________ were consistently located ________ or _________ other formations. formations above below

68. From these observations they established a ______ ____ ______ with a sequence of fossil groups from ______ to ______________ relative time scale oldest youngest

69. Each of these groups was named for a location where its ____________ ______ could be observed in the rocks. Characteristic fossil Example: Devon fossil “ Devonian ” found in Devon England

70. Further observations from around the world established a ________ _____ _____ Geologic time scale

71. Based on __________________________________ and ________________ ________ _____ _____ Inferred positions of Earth’s Landmasses Major Geologic Events (ex. Ice ages & Orogenys)

72. An ________ is the process of mountain building TURN TO PAGES 8 & 9 IN YOU ESRT! Orogeny

75. GEOLOGIC EVENTS OF THE PAST: _________ causes gaps in the geologic record. Erosion MISSING LAYERS

76. When a new layer of rock is laid down on a surface that has been _______ it forms a buried erosional surface or an ___________________ Eroded, unconformity

77. NEW BOTTOM LAYER APPEARS (EMERGES)

78. LAYER C IS MISSING EROSION

79. EROSION

80. THE UNCONFORMITY IS THE BURIED EROSIONAL SURFACE BETWEEN B AND D

83. ACTIVITY WHICH IS OLDER

84. VII. RADIOACTIVE DATING: A. Fossils enabled geologists to give ___________ time, relative

85. Relative Time Compares rock ages to _______________. Ex: The Limestone is older than the Sandstone. each other

86. However, B. Measurements of natural ___________in ( metamorphic and igneous) rocks have allowed the _________ time scale to be an ________ time scale. geologic absolute radioactivity

87. The _________ _____ of an object is measured in years. Ex: The limestone formed 5 mya and the sandstone formed 2 mya absolute age

88. C. Chemical elements often have several forms called _______________ isotopes

89. ISOTOPE: An unstable element with different number of neutrons than a normal (stable) element. (Its unstable so wants to change to stable)

90. EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons Unstable 8 neutrons

91. EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons 8 neutrons unstable

92. D. If the nucleus has more or fewer than the normal number of ____________, the isotope may be ____________ neutrons radioactive (unstable)

93. E. A radioactive isotope will break down naturally into a lighter element called _____ ________ which is stable. decay product

94. This process is called… Radioactive Decay

95. RADIOACTIVE DECAY: WHEN AN UNSTABLE ________ ELEMENT CHANGES INTO A COMPLETELY DIFFERENT (BUT STABLE) __________ ELEMENT DAUGHTER PARENT

96. F. A sample starts out at “Time zero” with _______ Percent of radioactive material. 100

97. Time Zero: when the sample is originally formed by cooling or solidification of igneous or metamorphic rock

98. As time goes by and the sample gets older, the radioactive element decay, and _______ radioactive atoms remain in the sample. fewer

99. Therefore, the higher the ratio of decay product to the radioactive element, the _____ the sample. older

100. The ratio between the mass of the radioactive element and its decay product in a sample is the _______________ decay product ratio

101. G. The decay of the parent atoms in a sample to daughter atoms is a _________ process… random

102. That happens at _____________ rates for different radioactive elements. Lets model this with pennies… different

103. H. The rate of decay of a radioactive element is measured by its’ _______ _________ half life

104. HALF-LIFE: THE AMOUNT OF TIME IT TAKES FOR HALF OF THE UNSTABLE ATOMS IN A SAMPLE TO CHANGE TO THE STABLE DECAY PRODUCT

105. Original=100% Decay product=0% 100/0 Or 1 to 0

106. Original=50% Decay product=50% 50/50 Or 1 to 1 After one Half-life:

107. Original=25% Decay product=75% 25/75 Or 1:3 After two Half-lives:

108. Original=12.5% Decay product=87.5% 12.5/87.5 After three Half-lives:

109. Original=6.25% Decay product=93.75% 6.25/93.75 After four Half-lives:

110. N 14 Ar 40 Pb 206 Sr 87 5.7 x 10 3 1.3 x 10 9 4.5 x 10 9 4.9 x 10 10 Element Decay Product Half-life

111. H. Calculating the age of a rock: 1. What would be the age of the rock if it has equal amounts of C-14 and its decay product N-14?

112. One half life has gone by 5.7 x 10 3 years or 5,700 years

113. 2.What % of the sample is radioactive after the following half-lives, 1 half-life 2 half-lives 3 half-lives 50% 25% 12.5%

114. 3. After 11,200 years how much C-14 would remain in a 10 gram sample? 25% or 2.5 grams 1/4 of the original amount

115. I. Selecting the Best Radioactive Element: 1. Under 50,000 years 2. Over 50,000 years Use Carbon-14 Use Uranium-238

116. Carbon 14 is used for dating organic material And ancient wood fires

117. “Time Zero” for carbon dating begins when the organism ___________ or when the ________ burns out. dies wood fire