Relative Dating

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You are as old as dirt or are you?

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Relative Dating

  1. 1. Relative Dating Chapter 13 Clues to Earth’s Past
  2. 2. Rules of Relative Dating <ul><li>Law of Superposition – the youngest layers are on the top and oldest on the bottom. </li></ul><ul><li>Layers are always laid down flat. </li></ul><ul><li>Uniformitarianism – processes happened in the past just as they happen today. </li></ul><ul><ul><li>Volcanic eruptions </li></ul></ul><ul><ul><li>Erosion </li></ul></ul><ul><ul><li>Fault movement </li></ul></ul><ul><li>Look out for unconformities !!! </li></ul><ul><li>*layers that are missing from erosion </li></ul>
  3. 3. Cross-cutting Relationships <ul><li>Intrusions –magma comes up into faults or between layers ( the layers were there 1 st ) </li></ul><ul><li>Faults crack the layers after they have formed ( the sidewalk is there before the crack ) </li></ul><ul><li>Folding of rock layers happens after they have been laid down flat. </li></ul>
  4. 4. 3 types of unconformities <ul><li>Like pages missing from the middle of a book </li></ul><ul><li>Erosion takes away layers leaving a gap in the rock record. </li></ul><ul><li>Correlation of rock sequences – by comparing rock layers from different areas a complete record of layers can be determined. </li></ul><ul><li>3 types </li></ul><ul><ul><li>Angular unconformity </li></ul></ul><ul><ul><li>Disconformity </li></ul></ul><ul><ul><li>Nonconformity </li></ul></ul>
  5. 5. Angular unconformities <ul><li>Horizontal sedimentary layers are TILTED when they are uplifted then eroded. </li></ul><ul><li>New sedimentary layers are deposited on top of this erosional surface. </li></ul><ul><li>Look for angles in the lower rock layers! </li></ul>
  6. 6. Disconformity <ul><li>Sedimentary rock layers were uplifted and eroded. </li></ul><ul><li>New sedimentary layers were added on top of this erosional surface. </li></ul><ul><li>The layers are ALL parallel. </li></ul><ul><li>There is a gap in the rock record. </li></ul>
  7. 7. Nonconformity <ul><li>Igneous or metamorphic rocks are uplifted and eroded </li></ul><ul><li>Sedimentary rocks are deposited on top of this erosion surface </li></ul><ul><li>The surface between the 2 different rock types is a nonconformity. </li></ul>
  8. 8. Which came first?
  9. 9. Answer key 1 2 3 6 4 8 9 11 12 7 5 10 13 erosion 6 intrusion 7 unconformity 10 fault

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