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Geologic Time

Geologic Time. Chapter 21.1-21.3. Geologic Time. Two frames of reference RELATIVE AGE DATING Places events in order according to their positions in the rock record ABSOLUTE AGE DATING Specific ages. Divided into: (p. 591) Eons Eras Periods Epochs. 21.2 Relative Age Dating.

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Geologic Time

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  1. Geologic Time Chapter 21.1-21.3

  2. Geologic Time • Two frames of reference • RELATIVE AGE DATING • Places events in order according to their positions in the rock record • ABSOLUTE AGE DATING • Specific ages

  3. Divided into: (p. 591) • Eons • Eras • Periods • Epochs

  4. 21.2 Relative Age Dating • Uniformitarianism • Geologic processes occurring today have been occurring since Earth formed • “present is the key to the past” • For example, waves crashing into shores now are just like waves crashing into shores millions of years ago

  5. Relative Age Dating • Six Principles • Principle #1: Superposition • Oldest layer on bottom, youngest on top

  6. Relative Age Dating • Principle #2: Original Horizontality • Sediments originally deposited horizontally

  7. Relative Age Dating • Principle #3: Lateral Continuity (not in book) • Layer continues equally in all directions; eventually “pinches” out

  8. Relative Age Dating • Principle #4: Cross-Cutting Relationships • Igneous intrusion or fault is younger than the rock it cuts across. fault cuts across Sedimentary layers

  9. Igneous dike cuts across granite.

  10. Sort from oldest to youngest • C B D E A http://science-dfjhs.web.nebo.edu/home/8th-grade/geology/geo3/g13

  11. Sort from oldest to youngest • D B C E

  12. Relative Age Dating • Principle #5: Inclusions • Rock fragments in a layer are older than the rock that contains them. This piece of rock has fallen into magma and became part of the igneous rock after the magma cooled. The rock “inclusion” is older than the magma it fell into.

  13. Relative Age Dating • Principle #6: Fossil Succession (Not in book) • Fossil assemblages succeed one another in a regular and predictable order • Index fossils (aka guide fossils) p. 609 • Geographically widespread • Existed for short geologic time • Easily identified • Abundant

  14. Index Fossils

  15. Unconformities • Surfaces which represent geologic time not represented in the rock record • 3 types

  16. Types of Unconformities • Disconformity: • Surface of erosion or non-deposition between beds which are parallel to one another

  17. Jurassic Disconformity

  18. Types of Unconformities • Angular Unconformity: • Erosional surface on tilted or folded strata over which younger strata are deposited.

  19. Angular Unconformity

  20. Types of Unconformities Nonconformity: horizontal sedimentary layer overlies non-sedimentary layer ?

  21. nonconformity Sedimentary rock Igneous rock

  22. ID the unconformities

  23. Correlation • The matching of unique outcrops or fossils exposed in one geographic region to similar outcrops in another geographic region. • This allows geologists to determine relationships between layers of regions that are far apart.

  24. Classwork/Homework • P. 599 • Do the Problem-Solving Lab

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