Determining Relative Age

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Determining Relative Age

• Section 17.1 by Andrea Robson and Christian Eib

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Principle of uniformitarianism

• a man in the 18th century named James Hutton
  invented it
• current geologic process such as volcanism and
  erosion are the same processes that were at work
  in the past

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How it works

• Layers of rock are called strata. Once the order
  of the formation of rocks is known, the relative
  age of the rocks can be determined
• Relative age indicates that any one layer is
  older or younger than another layer, NOT THE
  EXACT AGE OF THE ROCK!

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Law of Superposition

• An undeformed sedimentary rock layer is older
  than the layers above it and younger than the
  layers below it.
• If the layers arent horizontal then the law is
  not easily applied, then scientists need to find
  clues
• 1.) particle size
• 2.) shape of bedding plane
• 3.) ripple marks

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Uh oh, unconformities

• Are a break in the geologic record due to erosion
  or faulting.
• 3 types of unconformities are
• 1.) nonconformity stratified rests on
  unstratified rock
• 2.) angular the boundary between tilted
  and horizontal layers
• 3.) disconformity boundary between layers
  of rock that have not been deposited continuously

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Nonconformity
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Angular
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Disconformity
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Cross-cutting relationships

• Is used to determine the relative ages of rock
  layers, faults, and intrusions
• You can tell of a rock or intrusion is younger
  than the rock it cuts through

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Cross-Cutting Relationships