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Relative Age

Relative Age. The relative age of rocks refers to the order in which they occurred When something is dated in a relative manner, we can say “This layer of rock is older than this layer” We cannot say “This layer of rock is 5000000 years old. Principle of original horizontality.

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Relative Age

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  1. Relative Age • The relative age of rocks refers to the order in which they occurred • When something is dated in a relative manner, we can say “This layer of rock is older than this layer” • We cannot say “This layer of rock is 5000000 years old

  2. Principle of original horizontality • Original Horizontality: sedimentary layers are initially deposited in horizontal layers

  3. Law of Superposition • Older layers are found towards the bottom in a series of layers. • Younger layers are found towards the top.

  4. Crosscutting Rule • Any event that disturbs a rock is always more recent (younger) than the rock itself. • Clearly, the rock must be in place before something can happen to it.

  5. Geological Detective Work • Two trees have fallen in the forest. How could you find out which occurred first? • Law of superposition (if one fell on the other) • snowfall • moss buildup • decay

  6. When volcanoes erupt, they can leave a layer of ash over thousands of miles. This layer can be used to help date deposits in a relative manner. • See Figure 12.13 on p. 265

  7. Which Came First? W L E J C - fracture

  8. Which Came First? S B G R -folding K H M - fracture

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