Evidence for Movement of Continents

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Evidence for Movement of Continents
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Biggest obstacles to acceptance

• You can not see the continent move
• You can not feel the motion of the continent
• Yet a lot of physical evidence supports the idea
  that the continents move across the earth over
  time

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Goal for this section

• Review the evidence that supports continental
  drift
• Understand the process that allows continents to
  move (theory of plate tectonics)
• Predict what happens to continents and the life
  on them as they move

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Question

• What kind of physical evidence could be used to
  show that continents move?

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Alfred Wegener
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Alfred Wegener

• First proposed that continents move over time
  (continental drift) in early 20th century
• Meteorologist and German (what effect on
  acceptance of his ideas did his background have)
• Could not explain how continents move, led to
  rejection of theory

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Evidence for continental drift

1. Physical shape of continents
2. Rock evidence of change in climate
3. Fossil evidence, including Mesosaurus
4. Location of volcanoes and earthquakes
5. Difference in ages of oceanic crust vs
   continental crust. Relate age to plate
   boundaries
6. Magnetic orientation of rock on either side of
   the Mid Atlantic ridge

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Shape of the continents
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Pangaea and Panthalassa
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Pangea or Pangaea

• Pangaea- name of supercontinent the last time the
  continents were joined
• Panthalassa- name of the single ocean that
  existed at the same time as Pangaea

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Evidence for movement of continents
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Fossil evidence
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• Different animals and plants require certain
  climate conditions to live
• When the fossils found do not match current
  climate
• How did the climate change so much?

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Fossils of ferns found in Antarctica
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Mesosauras

• Small aquatic reptile
• Less than 3 ft long
• Breathed air
• Freshwater hunter
• Fossils found only in eastern South America and
  western Africa

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The mystery

• In the 1800s, scientists began finding fossils of
  these ancient reptiles, which had long since
  become extinct. These fossils were found in only
  two regions, southern Africa and the southern
  part of South America. The shaded areas on the
  map show where fossils of Mesosaurus have been
  discovered. This distribution is a curious
  oneonly two regions far from each other and
  separated by the Atlantic Ocean.
• What could explain this distribution?

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From experience with modern plants and land animal

• Migrate and expand primarily over land, not
  oceans.
• How can the exact same land animal or plant
  species have existed on a number of unconnected
  continents ?

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Possible answers

• Either the animals evolved the same all over the
  world (not consistent with recent evolution)
• Or
• The places were connected and closer in the past

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Paper Exercise

• Use the fossil evidence of shown to reassemble a
  supercontinent made from South America, Africa,
  Antarctica, India and Austraila
• Remember, all regions of the same fossil must
  connect
• It is ok to slightly overlap continents
• Glue final answer in your comp book

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point of exercise

• Areas where fossils of land animals/plants
  located must be connected
• This is possible only if Continents can move

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Microfossils

• Very small life forms, organic matter
• Diatoms in ocean
• Algae, pollen on land
• Localized
• Quick evolution

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Rock evidence

• Rock Type indicate climate
• Change in climate suggest requires change

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Coal

• Made from organic remains of vast jungle swamps
• Indicates a tropical environment

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Gypsum

• Created from what remains after ocean water has
  completely evaporated
• Indicates a hot, dry environment

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Rock Evidence for glaciers

• Deposits made up of rocks with different size,
  composition, and roughness

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Evidence of Glaciers

• Striations

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Location of volcanoes and earthquakes around the
world
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World Volcanoes
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World Earthquakes
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Volcanoes (triangles) Earthquakes (circles)
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Location of volcanoes and Earthquakes

• Volcanoes and earthquake line up, not randomly
  placed around the world
• Something must be happening on a global scale to
  account for this match

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Difference in the maximum ages of ocean and
continental rocks

• Max Oceanic Rock 180 million Years old
• Max Continental Rock over 4 Billion years old
• If continents did not move, both types should
  have similar ages

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Age of the sea floor

• Red young
• Blue old
• Connect lines created by earthquakes to ages

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• Oldest Oceanic crust is farthest away from the
  ocean ridges
• Newest Oceanic rock is found at the oceanic ridges

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Location of worlds Oldest rocks
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Question

• We have fossil evidence that oceans have been
  around for longer than 180 million years
• It was destroyed by a continuing process-
  suggests motion of ocean crust

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Paleomagnetism
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Paleomagnetism

• Study of the Earths magnetic record over time
• Many rocks contain magnetic minerals
• When these rocks are hot, the magnetic
  orientation of the minerals are random
• As they cools, the magnetic orientation of the
  minerals is fixed in the direction of the
  magnetic field of earth

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What is magnetic orientation?

• Means the direction the compass points when
  moving over the rock

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Surprising Data

• Some rocks have a magnetic orientation different
  from the orientation of Earth
• In the 1960s researchers mapping the orientation
  of rock across the Mid Atlantic ridge found a
  strangely symmetric result

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Different colors represent rocks with different
magnetic orientation
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What has been discovered

• Discovered bands of rock with different magnetic
  orientation as the ship moves away from ridge
• Evidence that the orientation reverses every
  200,000 to several million years
• Matched bands with the same magnetic orientation
  are found on both sides of a ridge