The Plate Tectonic Theory

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The Plate Tectonic Theory
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Alfred Wegener
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Alfred Wegener

• In the early part of the 20th century he noticed
  how continents seemed to fit together.
• He noticed that fossils of identical animals were
  being found on continents separated by thousands
  of kilometres.

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Alfred Wegener

• He also gathered evidence of similar rock
  formations on continents thousands of kilometres
  from each other.

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Alfred Wegener

• So in 1912 he published his theory That 180-200
  million years ago there was only one giant
  continent on Earth.
• He named this supercontinent Pangaea meaning
  all-Earth.

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Alfred Wegener

• He believed this supercontinent then broke into
  pieces, or giant plates, that drifted away from
  each other.

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Alfred Wegener

• This became the Plate Tectonic Theory.

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Earths Major Plates
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The Plate Tectonic Theory

• Question How much do the plates move?

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The Plate Tectonic Theory

• Question How much do the plates move?
• Answer About 2-5 cm a year.

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The Plate Tectonic Theory

• Question How much do the plates move?
• Answer About 2-5 cm a year.
• Thats not very much!!

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Lets do the math
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Lets do the math

• 5 cm/year

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Lets do the math

• 5 cm/year x 500 million years

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Lets do the math

• 5 cm/year x 500 million years
• 5 cm/year x 500 000 000 years

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Lets do the math

• 5 cm/year x 500 million years
• 5 cm/year x 500 000 000 years
• 2 500 000 000 cm

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Lets do the math

• 5 cm/year x 500 million years
• 5 cm/year x 500 000 000 years
• 2 500 000 000 cm
• 25 000 km Thats a lot!!!

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The Plate Tectonic Theory

• Question What make the plates move?

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The Plate Tectonic Theory

• Question What make the plates move?
• Answer Heres the leading hypothesis

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Convection Currents
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Convection Currents
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Convection Currents

• Radioactive materials deep in the mantle produce
  areas that are hotter than others.
• The heated magma rises until it reaches the
  bottom of the plates. It pushes the plates apart,
  then cools and sinks back down to complete the
  cycle.

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Evidence for the Plate Tectonic Theory
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Evidence for the Plate Tectonic Theory

• More sensitive instruments can now measure the
  yearly movements of the continents.
• The discovery of the Mid-Atlantic Trench causing
  Sea-floor Spreading

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Evidence for the Plate Tectonic Theory
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Evidence for the Plate Tectonic Theory

• 3. Magnetic striping

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Magnetic Striping
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Plate Tectonic Theory

• Magnetic striping was the proof that ended the
  debate. The P.T.T. is now accepted as the
  explanation of what is really happening down
  below us.

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The End