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The earths Shifting Crust. Fault Line. A line of weakness in the rocks of the earth’s crust. Continental Drift (Pangaea). In early 1915, the German scientist Alfred Wegner developed a theory that the continents once formed a giant supercontinent that he called

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fault line
Fault Line
  • A line of weakness in the rocks of the earth’s crust
continental drift pangaea
Continental Drift (Pangaea)

In early 1915, the German scientist Alfred Wegner developed a theory

that the continents once formed a giant supercontinent that he called

Pangaea. He speculated that the Earth took this form about 245 million

years ago, during the Triassic period of the Mesozoic era. The Mesozoic

is the era in which dinosaurs lived. A few years after Wegner proposed

his theory, South African geologist Alexander Du Toit further theorized

that Pangaea divided into two supercontinents 205 million years ago. Du

Toit called the northern supercontinent Laurasia and the southern one

Gondwanaland. The scientists used many kinds of evidence to advance

their theories. They found similar fossil remains of plants and animals on

different present day continents.

plate tectonics
Plate Tectonics
  • We have learned that plates on the earth’s crust are slowly dragged together, apart, or sideways by the rolling motion of molten rock
  • Molten rock moves in convection currents.
when the plates move together
When the plates move together
  • As plates move together, land can either move up or down.
  • If they move up, they form fold mountains
  • If they move down, they create deep deep trenches as an ocean plate is hauled under a continent.
when plates move apart
When Plates move Apart
  • In the middle of the Atlantic Ocean, two plates are moving apart 3cm a year.
  • Molten rock pours through these cracks and over a long time span, cools and forms underwater mountains.
slide11

Plate Boundaries:

  • ConvergentWhere plates come together
  • Divergent Where plates move apart/away from each other
  • Transform Where plates are sliding past each other