19'2 Growth of a Continent: North America

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19.2 Growth of a Continent North America

• By Skylar and Riley
• Period 3

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Beginnings of a Continent

• The rock structure of an existing continent can
  reveal a general outline of its geologic history.
  The rock structure of North America indicates
  that during the Paleozoic Era, much of what is
  now North America was part of a larger continent.
  A shallow sea covered much of what now is the
  United States.
• Huge amounts of sediments were carried into the
  shallow water. Eventually, the sediments reached
  a thickness of over 12 km.
• As the Paleozoic Era ended 245 million years ago
  and the continents came together to form Pangaea,
  most of the warm shallow seas disappeared. The
  marine invertebrates that had been so abundant
  for more then 400 million years vanished almost
  entirely. The large inland sea that covered much
  of what was to become North America dried up
  which left behind huge deposits of salt now found
  buried deep in the Permian layers from Kansas to
  New Mexico.

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Shaping the Continent

• The burst of tectonic activity accompanying the
  breakup of Pangaea played a large role in shaping
  North America. The basic form of the continent
  was determined by the rifts that split Laurasia
  from Gondwanaland and North America from Eurasia.
• Much of what is now the Atlantic coastal area was
  once attached to the African plate. Some of the
  ancient European plate became welded onto parts
  of the present-day New England and Canada. In
  addition, new pieces of continental crust, called
  terranes, were added.
• Early in the Mesozoic Era, a large mountain
  range, the ancient Appalachians, existed along
  what is now the eastern United States. The
  Appalachians were created during the collision
  that formed Pangaea.
• By the late Mesozoic Era, the Appalachian
  Mountains had been quite worn out.

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The Modern Continent

• By the beginning of the Cenozoic Era, about 65
  million years ago, North America had begun to
  take on the shape it has today. The inland sea
  that covered much of the central region during
  Mesozoic times had drained away. Only the
  present coastal plain along the Atlantic and Gulf
  coasts remained submerged. These mountains,
  which first appeared during the Jurassic Period,
  were eroded until they were almost flat, then
  uplifted again during the Cenozoic Era.
• East of the Sierra Nevada, a series of tilted
  fault-blocks created a large area of alternating
  mounts and valleys.
• The Grand Canyon was created as the Colorado
  River cut into the rising land. Farther to the
  north, the Rocky Mountains continued to be pushed
  up.Volcanic activity has continued throughout the
  Cenozoic Era in the northwest. Washington,
  Oregon, and northern California are crossed by
  volcanic Cascade mountain range.

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Vocabulary

• Canadian Shield Exposed portion of the Craton
  around which North America has been built up.