How do we know that the continents have moved

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How do we know that the continents have moved?
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Evidence for continental drift

• Features of the ocean floor that provide evidence
  of plate tectonics
• Magnetic patterns
• Age of the ocean floor
• Sea-floor topography
• Much of the evidence for continental drift came
  from the seafloor rather than from the continents
  themselves.

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Midoceanic Ridge

• The longest topographic feature in the world is
  the midoceanic ridge systema chain of volcanoes
  and rift valleys about 40,000 miles long that
  rings the planet like the seams of a giant
  baseball

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Mid-Atlantic Ridge

• The ridge system is made from the youngest rock
  on the ocean floor, and the floor gets
  progressively older, symmetrically, on both sides
  of the ridge.

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Mid-Atlantic Ridge

• The oldest part of the ocean floor is not older
  than 200 million years old. Sediment is thin on
  and near the ridge.

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Seafloor Spreading

• Sediment found away from the ridge thickens and
  contains progressively older fossils, a
  phenomenon that also occurs symmetrically.

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Magnetic Striping

• Mapping the magnetic field anywhere across the
  ridge system produces a striking pattern of high
  and low fields in almost perfect symmetrical
  stripes. A brilliant piece of scientific
  detective work inferred that these zebra
  stripes arose because lava had erupted and
  cooled, locking into the rocks a residual
  magnetic field whose direction matched that of
  Earths field when cooling took place.

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Magnetic Striping

• When new rock is formed at the bottom of the
  ocean it locks in the earths magnetic field.

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Seafloor Spreading

• Proof 1 Magnetic stripes

• Proof 2 Age of sea floor

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Theory of Plate Tectonics

• This theory states that new seafloor is created
  by volcanic eruptions at the midoceanic ridge and
  that this erupted material continuously spreads
  out convectively and opens and creates the ocean
  basin.

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Continetal Margins

• At some continental margins deep ocean trenches
  mark the places where the oldest ocean floor
  sinks back into the mantle to complete the
  convective cycle.

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