Drifting Continents

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Drifting Continents

• Did Pangea Exist?

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The Theory of Continental Drift

• A German scientist named Alfred Wegener formed
  the hypothesis that the continents had moved!
• He proposed that all the continents had once been
  joined together in a single landmass and have
  since drifted apart.
• Wegener named this supercontinent Pangea.

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The Theory of Continental Drift

• Wegeners idea that the continents slowly moved
  over the earth became known as continental drift.
• Unfortunately Wegener could not provide a
  satisfactory explanation for the force that
  pushed or pull the continents. Therefore most
  geologists rejected his idea.

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Evidence of Continental Drift

• Evidence from landforms
• Mountain ranges and other features on the
  continents provided evidence for continental
  drift.
• Mountain ranges in South Africa line up with
  mountain ranges in Argentina.

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Evidence for Continental Drift

• Evidence from fossils
• A fossil is any trace of an ancient organism that
  has been preserved in rock.
• Glossopteris fossils have been found in rocks in
  Africa, South America, Australia, India, and
  Antarctica.

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Evidence for Continental Drift

• Evidence from climate
• Fossils of tropical plants have been found too
  far south to have survived.
• Glacier deposits are found too far north to have
  existed.
• These clues provide evidence that continental
  drift really happened.

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Rejection!!
Even with the evidence, most scientists rejected
Alfred Wegeners theory for about a half a
century, from the 1920s to the 1960s.
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Convection Currents in the Mantle

• Energy is constantly on the move!
• The movement of energy from warmer object to a
  cooler object is called a heat transfer
• There are three types of heat transfer
  radiation, conduction, and convection.

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Radiation

• Radiation is the transfer of energy through empty
  space.
• Heat transfer by radiation takes place with no
  direct contact between a heat source and an
  object.

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Conduction

• Heat transfer by direct contact of particles is
  called conduction.
• When your hands touches a metal spoon sitting in
  a boiling pot of soup, the heat from the bottom
  of the pot is transferred to you hand by
  conduction.

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Conduction
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Convection

• Convection is the transfer of heat by the
  movement of a heated fluid.
• Convection deals with density.
• Density is the measure of how much mass is there
  in a volume of a substance.

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Convection

• When a liquid or gas is heated, the particles
  move faster and the density decreases.
• As the fluid becomes cooler, its density
  increases.
• As density increases, the fluid sinks.
• Heat Rises!!

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Convection

• The heating and cooling of the fluid, changes in
  the fluids density, and the force of gravity
  combine to set convection currents in motion.
• Without heat, convection currents will eventually
  come to a stop.

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Convection in the Earths Mantle

• The heat source for these convection currents in
  the mantle comes from the heat of the Earths
  core.

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Radiation, Conduction, and Convection
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