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Drifting Continents

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Drifting Continents Did Pangea Exist? The Theory of Continental Drift A German scientist named Alfred Wegener formed the hypothesis that the continents had moved! – PowerPoint PPT presentation

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Title: Drifting Continents


1
Drifting Continents
  • Did Pangea Exist?

2
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.

3
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.

4
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.

5
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.

6
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.

7
Rejection!!
Even with the evidence, most scientists rejected
Alfred Wegeners theory for about a half a
century, from the 1920s to the 1960s.
8
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.

9
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.

10
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.

11
Conduction
12
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.

13
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!!

14
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.

15
Convection in the Earths Mantle
  • The heat source for these convection currents in
    the mantle comes from the heat of the Earths
    core.

16
Radiation, Conduction, and Convection
17
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