Fossils

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Fossils

• Earth History Part II

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Fossils

• Any part, remnant or evidence left by an organism
  in a rock
• Fossils are found in sedimentary rocks

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How Fossils are Formed

• Original Remains
• Actual unchanged remains
• Wooly Mammoths
• Replaced Remains
• Hard parts have been replaced by minerals
• Petrified wood

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How Fossils are Formed

• 5 ways
• Molds
• Casts
• Refrigeration
• Encasement
• Petrification

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How Fossils are Formed

• Mold
• Creature is dissolved completely out of the rock
  leaving a depression
• Cast
• New material fills the mold

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How Fossils are Formed

• Refrigeration
• Freezing organism
• Preserved in ice
• Wooly Mammoth in glaciers

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How Fossils are Formed

• Encasement
• Organism is enclosed by material that prevents
  decay
• Example
• Ants in amber
• Tar pits

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How Fossils are Formed

• Petrification (Mineral Replacement)
• Mineral crystals replace cells in the organism
• Example
• Petrified wood

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Trace Fossil

• Evidence of life other than the remains of a
  plant or animal
• Footprints
• Tracks
• Burrows
• Borings

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Index Fossil

• Fossils that are typical of a particular time
  segment of Earths history.

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3 Characteristics of Index Fossils

• 1.) Must be easily recognizable. Unique in some
  way so they can easily be told from other similar
  fossils.
• 2.) Must be widespread in occurrence
  geographically.
• 3.) Limited in time.
• 4.) Abundant

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Key Bed

• A single rock layer that has the same
  characteristics as an index fossil.
• Example A large volcanic eruption.

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Other Uses

• Fossils are also used to tell us about past
  climates.
• Fossils and microfossils are also used for
  correlation.

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Principle of Fossil Succession

• When fossils are arranged according to their age
  in sedimentary rocks, they show progressive
  changes and different groups of organisms coexist
  at different times.

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Hiatus location where the rock record is
missing one or more layers
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Fossil Evidence

• Direct
• Actual organism is preserved in some way
• Indirect
• A replica or model of the organism shape or an
  activity it made

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Which ones are direct?

• Refrigeration
• Encasement

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Which ones are indirect?

• Molds
• Casts
• Petrification

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K-T Boundary

• The divisions of the time scale were based on the
  observations that large percentages of animals
  and plants became extinct at certain intervals.
• The most talked about of these is the extinction
  at the end of the Cretaceous (KT extinction) .