Rock Record

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Rock Record

• Chapter 8

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Age of Rock

• Once believed that earth was only 6000 years old
• Thought nothing had gone extinct
• Through discovery scientists found earth was much
  older, and that life came before people

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Relative Age

• The age of an object in relation to others
• Law of Superposition
• A rock layer is older than those above it, young
  than those below it.
• True so long as the layers are not disturbed

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Unconformities

• Break in the geologic record created when rock
  layers are eroded
• Non-conformity unknown period of time where
  older rock is eroded and replaced with new
• Angular Unconformity horizontal layers are
  folded/tilted then eroded, new horizontal layer
  forms on top
• Disconformity Like non-conform, older layers
  are eroded away, new layers then form
  horizontally with the old

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Absolute Age

• Numeric age of an object or event established
  with radiometric dating or other similar method

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Types of Dating

• Rate of Erosion est. rate based on current
  data.
• Good only for 10,000 years
• Rate of Deposition est. rate based on amount of
  rock laid down
• 30cm of sediment is deposited in 1000 years
• Not always accurate because of weather changes

• Varve Count Like rings in a tree, banded layers
  deposited in a lake
• Radiometric Measures the differences between
  radioactive isotopes stable isotopes
• Half-life time required for half the sample to
  break down
• Always stays the same
• Uses U has the longest half life

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• Carbon Dating Uses radioactive C14 to age rock
  samples
• Needs to be less than 70,000 years old contain
  organic materials

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Fossils

• Traces or remains of an organism that lived long
  ago, preserved in a rock (Sedimentary)
• Used to help date rocks (C14 dating)
• Provides clues about past events, climate, and
  evolution
• Paleontologists- person who studies fossils

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Types of Fossils

• Mummification
• Remains in very dry places
• Amber
• Harden tree sap
• Tar Seep
• Thick petroleum
• Covered with water, can trap unsuspecting animals

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• Freezing
• Trapped or buried organisms that do not decay
• Petrification
• Minerals replace the original organic material
• Imprints
• Imprints of leaves, prints, or exoskeletons made
  in soft mud

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• Molds
• Shells leave empty spaces that fill with mud and
  harden
• Coprolites
• Fossilized dung or waste.
• Used to reveal feeding habits
• Gastroliths
• Stones from dinosaur's stomachs

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