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Interpreting geologichistoryupdated2


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Interpreting geologichistoryupdated2

  1. 1. Interpreting Geologic History
  2. 2. THE PRINCIPLE OF UNIFORMITY: <ul><li>Geologists can infer events of the past by </li></ul>Looking at features of rocks and rock outcrops
  3. 3. Uniformitarianism (Principle of <ul><li>states that the forces that acted upon the </li></ul><ul><li>___________ crust… </li></ul>Uniformity) Earth’s
  4. 4. <ul><li>in the __________ are the same as those that are ____________ </li></ul><ul><li>today. </li></ul>past active ** THE KEY TO THE PAST IS THE PRESENT**
  5. 5. Relative Dating Techniques
  6. 6. 5 Basic Laws: <ul><li>1. Law of Original Horizontality </li></ul><ul><li>2. Law of Superposition </li></ul><ul><li>3. Law of Inclusions </li></ul><ul><li>4. Law of Cross-Cutting Relationships </li></ul><ul><li>5. Law of Original Lateral Continuity </li></ul>
  7. 7. Law of Original Horizontality <ul><li>Strata is originally </li></ul><ul><li>deposited in flat horizontal layers because sedimentary particles settle from air and water under the influence of gravity </li></ul>
  8. 8. Law of Original Horizontality <ul><li>If strata are ___________, then they must have suffered some kind of disturbance after they were deposited. </li></ul>Grand Canyon Western Iran Steeply Inclined
  9. 9. THE LAW OF SUPERPOSITION: <ul><li>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___________ </li></ul>bottom before disturbed uplifted
  10. 10. <ul><li>The _______ rocks are found at the bottom. </li></ul><ul><li>Geologists can date the </li></ul><ul><li>_________ ages of the strata from </li></ul><ul><li>________ to __________ </li></ul>older relative oldest youngest
  11. 11. oldest youngest
  12. 12. Law of Superposition <ul><li>Therefore the order of deposition is from the bottom upward. </li></ul>
  13. 13. Law of Inclusions <ul><li>A rock must first exist in order to be weathered, deposited and cemented as a _____ in another rock. Therefore… </li></ul>clast
  14. 14. <ul><li>If rock is composed of _____________, the rock fragments must be ___________ than the rock in which they are found. </li></ul>fragments older
  15. 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. 16. <ul><li>The law of inclusions also applies to fossils preserved in the bedrock. </li></ul>
  17. 17. <ul><li>_________ are any naturally preserved remains or impressions of living things. </li></ul>Fossils
  18. 26. <ul><li>They are found in _______________ because </li></ul><ul><li>_____________________ </li></ul><ul><li>____________ </li></ul>Sedimentary rock Heat & pressure in igneous and metamorphic rock destroys them
  20. 28. Law of Cross-Cutting Relationships <ul><li>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. </li></ul>Igneous rock fault
  21. 29. <ul><li>In general rock is always_________ than the process that changed it. </li></ul>older
  22. 30. Some Processes Include: <ul><li>folds </li></ul><ul><li>faults </li></ul><ul><li>tilts </li></ul><ul><li>intrusions </li></ul><ul><li>extrusions </li></ul>
  23. 31. Sedimentary layers (the law of original horizontality)
  24. 32. Sedimentary layers
  25. 33. Sedimentary layers
  26. 34. Sedimentary layers
  27. 35. Sedimentary layers
  28. 36. The fault came after the rock was formed
  29. 37. Sedimentary layers The tilt came after the the rock was formed
  30. 38. The extrusion came after the rock was formed 1 2 3 4 5 Contact metamorphism
  31. 39. 1 2 3 4 5 6 The extrusion came after the lower layers were formed but…. Before the top layer
  32. 40. 1 2 3 4 5 This intrusion came after all the layers
  33. 42. <ul><li>These changes can lead to exceptions to the Law of Superposition: </li></ul><ul><li>a.An __________ is </li></ul><ul><li>an igneous rock that formed from lava on the surface of the crust. </li></ul>extrusion
  34. 43. <ul><li>An __________ must be younger than the strata below it, but ________ than any layers above. </li></ul>extrusion older
  35. 44. <ul><li>b. __________ are created when molten rock (________) is injected into older rock layers in the crust. </li></ul>intrusions magma
  36. 45. <ul><li>_____________ are </li></ul><ul><li>_____________ than </li></ul><ul><li>all the rock layers in contact with them. </li></ul>Intrusions younger
  37. 46. <ul><li>c. _______ are bends </li></ul><ul><li>in the rock strata. ________ can overturn rock strata so that ________ rock lies on top of _________ rock. </li></ul>Folds folding older younger
  38. 49. <ul><li>d. _______ are cracks </li></ul><ul><li>in rock strata. </li></ul><ul><li>_______ produce offset layers. </li></ul>Faults Faults
  39. 50. <ul><li>d. _______ are cracks </li></ul><ul><li>in rock strata. </li></ul><ul><li>_______ produce offset layers. </li></ul>Faults Faults
  40. 51. <ul><li>Rock strata must be </li></ul><ul><li>________ than the process that changed it. </li></ul>older
  41. 52. <ul><li>_________, ________ and ________ ___________ </li></ul><ul><li>are features created after rock or sediment has been deposited. </li></ul>cracks veins natural cement
  42. 54. Law of Original Lateral Continuity <ul><li>. 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 __________. </li></ul>deposition
  43. 55. Law of Original Lateral Continuity
  44. 56. Law of Original Lateral Continuity <ul><li>This concept enables us to correlate outcrops of strata that has been dissected by processes of ________. </li></ul>erosion
  45. 57. CORRELATION OF ROCK STRATA: <ul><li>Correlation is </li></ul>Matching similar rock strata at different locations to see if they formed at the same time
  46. 58. Ways to correlate rock formations: <ul><li>“ Walking the outcrop” </li></ul><ul><li>is done by </li></ul>Walking from end to end
  47. 59. <ul><li>This is correlation by </li></ul>continuity
  48. 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
  49. 61. Time correlation compares ____________ contained in the rock strata index fossils 1 2 3 4 4 5 6 3
  50. 62. The best index fossils: <ul><li>a. _________________ </li></ul><ul><li>b. _________________ </li></ul>Exist for a brief period of time are widespread
  51. 63. Which fossil would make the best index fossil? Found in only 1 layer (short lived) Found in all samples (widespread)
  52. 64. Another way of correlating layers by time is through ___________________ Volcanic ash falls
  53. 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
  54. 66. GEOLOGIC TIME SCALE: <ul><li>A. Geologists noticed that rock _________ can be identified by the fossils they contained. </li></ul>formations
  55. 67. <ul><li>They also found that certain __________ were consistently located ________ or _________ other formations. </li></ul>formations above below
  56. 68. <ul><li>From these observations they established a </li></ul><ul><li>______ ____ ______ </li></ul><ul><li>with a sequence of fossil groups from ______ to </li></ul><ul><li>______________ </li></ul>relative time scale oldest youngest
  57. 69. <ul><li>Each of these groups was named for a location where its ____________ ______ could be observed in the rocks. </li></ul>Characteristic fossil Example: Devon fossil “ Devonian ” found in Devon England
  58. 70. <ul><li>Further observations from around the world established a </li></ul><ul><li>________ _____ _____ </li></ul>Geologic time scale
  59. 71. <ul><li>Based on __________________________________ </li></ul><ul><li>and ________________ </li></ul><ul><li>________ _____ _____ </li></ul>Inferred positions of Earth’s Landmasses Major Geologic Events (ex. Ice ages & Orogenys)
  60. 72. <ul><li>An ________ is the process of mountain building </li></ul><ul><li>TURN TO PAGES 8 & 9 IN YOU ESRT! </li></ul>Orogeny
  61. 75. GEOLOGIC EVENTS OF THE PAST: <ul><li>_________ causes gaps in the geologic record. </li></ul>Erosion MISSING LAYERS
  62. 76. <ul><li>When a new layer </li></ul><ul><li>of rock is laid down on a surface that has been _______ it forms a buried erosional surface or an </li></ul><ul><li>___________________ </li></ul>Eroded, unconformity
  65. 79. EROSION
  68. 84. VII. RADIOACTIVE DATING: <ul><li>A. Fossils enabled geologists to give ___________ time, </li></ul>relative
  69. 85. Relative Time <ul><li>Compares rock ages to _______________. </li></ul><ul><li>Ex: The Limestone is older than the Sandstone. </li></ul>each other
  70. 86. However, <ul><li>B. Measurements of natural ___________in ( metamorphic and igneous) rocks have allowed the _________ time scale to be an ________ time scale. </li></ul>geologic absolute radioactivity
  71. 87. <ul><li>The _________ _____ of an object is measured in years. </li></ul><ul><li>Ex: The limestone formed 5 mya and the sandstone formed 2 mya </li></ul>absolute age
  72. 88. <ul><li>C. Chemical elements often have several forms called _______________ </li></ul>isotopes
  73. 89. ISOTOPE: An unstable element with different number of neutrons than a normal (stable) element. (Its unstable so wants to change to stable)
  74. 90. EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons Unstable 8 neutrons
  75. 91. EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons 8 neutrons unstable
  76. 92. D. If the nucleus has more or fewer than the normal number of ____________, the isotope may be ____________ neutrons radioactive (unstable)
  77. 93. <ul><li>E. A radioactive isotope will break down naturally into a lighter element called </li></ul><ul><li>_____ ________ which is stable. </li></ul>decay product
  78. 94. This process is called… Radioactive Decay
  80. 96. <ul><li>F. A sample starts out at “Time zero” with _______ Percent of radioactive material. </li></ul>100
  81. 97. <ul><li>Time Zero: when the sample is originally formed by cooling or solidification of igneous or metamorphic rock </li></ul>
  82. 98. <ul><li>As time goes by and the sample gets older, the radioactive element decay, and _______ radioactive atoms remain in the sample. </li></ul>fewer
  83. 99. <ul><li>Therefore, the higher the ratio of decay product to the radioactive element, the _____ the sample. </li></ul>older
  84. 100. <ul><li>The ratio between the mass of the radioactive element and its decay product in a sample is the _______________ </li></ul>decay product ratio
  85. 101. <ul><li>G. The decay of the parent atoms in a sample to daughter atoms is a _________ process… </li></ul>random
  86. 102. <ul><li>That happens at _____________ rates for different radioactive elements. Lets model this with pennies… </li></ul>different
  87. 103. <ul><li>H. The rate of decay of a radioactive element is measured by its’ _______ _________ </li></ul>half life
  89. 105. Original=100% Decay product=0% 100/0 Or 1 to 0
  90. 106. Original=50% Decay product=50% 50/50 Or 1 to 1 After one Half-life:
  91. 107. Original=25% Decay product=75% 25/75 Or 1:3 After two Half-lives:
  92. 108. Original=12.5% Decay product=87.5% 12.5/87.5 After three Half-lives:
  93. 109. Original=6.25% Decay product=93.75% 6.25/93.75 After four Half-lives:
  94. 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
  95. 111. <ul><li>H. Calculating the age of a rock: </li></ul><ul><li>1. What would be the age of the rock if it has equal amounts of C-14 and its decay product N-14? </li></ul>
  96. 112. One half life has gone by <ul><li>5.7 x 10 3 years </li></ul><ul><li>or 5,700 years </li></ul>
  97. 113. <ul><li>2.What % of the sample is radioactive after the following half-lives, </li></ul><ul><li>1 half-life </li></ul><ul><li>2 half-lives </li></ul><ul><li>3 half-lives </li></ul>50% 25% 12.5%
  98. 114. <ul><li>3. After 11,200 years how much C-14 would remain in a 10 gram sample? </li></ul>25% or 2.5 grams 1/4 of the original amount
  99. 115. I. Selecting the Best Radioactive Element: <ul><li>1. Under 50,000 years </li></ul><ul><li>2. Over 50,000 years </li></ul>Use Carbon-14 Use Uranium-238
  100. 116. <ul><li>Carbon 14 is used for dating </li></ul><ul><li>organic material </li></ul><ul><li>And ancient wood fires </li></ul>
  101. 117. <ul><li>“Time Zero” for carbon dating begins when the organism ___________ or when the ________ burns out. </li></ul>dies wood fire