Chapter 7: Changing Continents and Climates

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Chapter 7 Changing Continents and Climates
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19th Century Geology

• Law of Superposition 19th century geologists
  assumed that strata lower in the stratigraphic
  exposure were older than the overlying strata
• Law of Uniformitarianism assumes that processes
  that weathered, eroded, and deposited rock in the
  past were the same as those operating today
• These laws used to develop geologic time scale

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Alfred Wegener

• 1912 Theory of Horizontal Displacement of the
  Continents similarities between Atlantic
  coastlines
• Theory of Continental Drift (1912-1929)
• Crust of continents composed of relatively light
  rocks. Ocean floors largely composed of dense
  basalts. Lighter continental rocks could float on
  viscous mantle of Earth and override oceanic crust

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Alfred Wegener

• Permian glacial deposits in Brazil, South Africa,
  India, and Australia indicates that tropical
  areas once glaciated, so they must have been
  close to the poles at one time
• Similarities in the shapes of continents, their
  geology, and fossils suggest closer proximity in
  the past
• Geodetic measurements of latitude and longitude
  of Greenland indicated westward movement of the
  landmass
• Continental Drift led to Plate Tectonics

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Alfred Wegener

• Pangaea
• Gondwanaland Africa, South America, Australia,
  Antarctica, and India
• Laurasia North America, Europe, and Asia
• Pangaea formed 195 mya began to break up 180
  mya with formation of Atlantic Midoceanic Ridge

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Figure 7.3
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Vindication Alfred Wegener

• Lystrosaurus Triassic reptile fossils found in
  Antarctica, Africa, and India Antarctica must
  have been warmer in the past

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Vindication Alfred Wegener

• Galaxioidea freshwater fish family found in
  southern South America, South Africa, Australia,
  and New Zealand must have been connected in the
  past
• WWII sea floor mapping by submarines

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• Paleomagnetism ancient igneous rocks are little
  compasses
• iron or titanium point to their magnetic north
• compare this to current magnetic north to
  determine where continents used to lie

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Figure 7.6
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Glaciation

• Radiocarbon dating based on measuring the
  amount of the radioactive isotope carbon 14 found
  in plant and animal remains
• Greenland ice cores extend 100,000 years
• Antarctic ice cores extend 400,000 years
• Ice cores provide record of atmospheric chemistry
• 18O isotopes deposited during warmer times 16O
  isotopes deposited during cooler times

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Figure 7.7
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Relationship between atmospheric temperature and
18O isotopes
Figure 7.9