Fossils and the Rock Record Ch 21 page 588

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Fossils and the Rock RecordCh 21 page 588
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Geologic Time Scale

• Based on fossil evidence found in rock
• Divided into units
• EONS (largest)
• ERAS
• PERIODS
• EPOCHS (smallest)

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Evidence for the formation of earth
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Ways to figure out Earths age

• Relative Age- dating
• Things older are underneath the newer in terms of
  position in the earth by COMPARISON.
• But it does NOT provide a DATE!

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Types of Relative-Age dating

• 1. Original horizontality layering occurs in
  horizontal lines due to gravity, wind, water
• 2. Superposition without a disturbance, older
  rocks will always be at the bottom
• 3. Cross-cutting relationships intrusions are
  younger than the rock that they cut through

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Uniformitarianism

• Processes that were happening years ago, are
  still happening now!

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Continued

• 4. Inclusions these fragments are eroded and
  then deposited into surrounding rock making these
  fragments older!
• 5. Unconformities any erosional surface
  separating 2 layers of rock that have been
  deposited at different times
• 6. Correlation matching of unique rock/fossils
  in different geog. areas.

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ABsolute-Age dating techniques

• Absolute Age-dating
• Things are older or newer based on actual age!
• ex radioactive decay
• - half-lives
• - radiocarbon dating
• - tree rings
• - ice cores

• 1.radioactive decay loss of neutrons from
  nucleus
• 2. half-lives amount of time it takes for ½ to
  decay.
• 3. radiocarbon dating measures C-14 left in
  dead organism to date it