How do we reconstruct geologic history?

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How do we reconstruct geologic history?
Relative age-dating
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What happened to form these rocks?
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What happened here?
Cgl
SS and Sh
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How about here?
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Relative Age-Dating

• Study rock properties and sequence
• Look at modern analogs
• Create chronology of events based on common
  sense set of principles
• James Hutton set forth principles
• Scottish
• 1726-1797
• Father of modern geology
• Charles Lyell
• Scottish
• 1797-1875

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Map Lithologic Symbols
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Basic principles of relative age-dating

• Uniformitarianism
• Original horizontality

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Young F B K N A J D M H C L G E Old

• Superposition
• Cross-cutting relationships
• Included fragments
• Fossils
• Unconformities