The Fossil Record

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The Fossil Record

• Mrs. Kerstetter
• General Science 7

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The Fossil Record

• Fossils
• preserved remains or traces of an organism that
  lived in the past
• Can be formed from
• a bone, tooth, shell, or other part of an
  organism
• Also traces of organisms (footprints, burrows)

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The Fossil Record

• How do fossils form?
• -usually only of hard parts (bone, shells)
• -usually not complete
• -can be formed by plants
• Rare to form fossils!
• -need to be buried in sediments (rock/soil)
• -over years layers form sedimentary rock

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Fossil Formation
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Fossil Formation
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Fossil Formation
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The Fossil Record

• Petrified Fossils
• -some remains change to rock
• -minerals replace remains
• Molds and Casts
• -some remains dissolve leaving an empty space
  (MOLD)
• -if mold fills with hardened minerals (CAST)

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The Fossil Record

• Preserved Remains
• -mammoths in ice
• -tar pits
• -sap from trees-hardens into amber

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Determining a Fossils Age

• Two ways
• 1. Relative Dating
• 2. Absolute Dating
• Relative Dating
• -use rock layers to determine age of fossil
• -does NOT tell actual age

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Determining A Fossils Age

• Absolute Dating
• -determines ACTUAL age
• -uses radioactive elements found in fossil
• -half-life
• time it takes half of atoms to decay in a
  sample
• -scientists compare the amount of the
  radioactive element to the element it breaks down
  into
• See page 160 Figure 10

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The Fossil Record

• Helps us to infer when new species or groups of
  organisms evolved.
• The Geologic Time Scale
• a calendar of Earths history
• -covers more than 4.6 BILLION years
• -time is divided into PERIODS or ERAS

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The Fossil Record

• Geological Time Scale (cont)
• largest span of time is Precambrian Time
• -first 4 billion years
• -few fossils from this period

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The Fossil Record

• How fast does evolution occur?
• One theory Gradualism
• gt evolution occurs slowly but steadily
• -what Darwin thought
• 2nd Theory Punctuated Equilibria
• gtspecies evolve during short periods of rapid
  change
• -by Stephen Jay Gould Niles Eldridge
• Both types have seemed to occur during Earths
  history!