SHEILDS
PLAINS
LOWLANDS
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LANDFORM PATTERNS
 Geographers are interested in patterns o the earth.
They use arrangement of cities, landforms, or river
systems to help them identify unique regions.
 You learned that most active volcanoes are located at
plate boundaries, especially around the Pacific Ring of
Fire.
 We will be discussing examples of landform patterns
in North America – such as shields, plains, and
lowlands
Plate Tectonics
 PLATE TECTONICS – the theory that all the
continents were once joined together and are gradually
drifting apart.
 During the earth’s 4.6 billion – year history, land
masses have been built up and then worn away many
times.
 Scottish geologist James Hutton first advanced this
idea in 1785, but most scholars rejected it.
 At the time, scientists thought the earth was only 6000
years old, but this was too little time for so much
change to have happened.
PANGAEA
 German geographer Alfred Wegener was another
landform pioneer.
 In 1912, he proposed that all of the continents were
once joined together in on huge land mass named
Pangaea.
 His theory was also criticized, but is now considered a
key to understanding landform patterns.
 The modern theory of Plate Tectonics is built upon
Wegener’s work
SHIELD REGIONS
 Pangaea was built around old shield regions. These
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regions were created by widespread volcanic activity
billions of years before.
They are largely composed of igneous rock; that is,
solidified magma. Later, heat and pressure altered
some parts of these old shield regions.
This formed metamorphic rock, or changed rock.
As Pangaea broke apart, the shield regions were
scattered across the earth as the core of the continents.
Today, they are heavily worn and carved by the
relentless forces of erosion – water, ice, and wind.
PLAINS AND LOWLANDS REGIONS
 The erosion of the shield regions created the rest of the
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continent Rivers and glaciers carried eroded material,
called sediment into ancient seas.
There, it accumulated into thick beds that slowly solidified
into sedimentary rock – (thick beds of sediment that have
slowly solidified into rock)
New land emerged around the ancient shields as the seas
filled in. These plains and lowlands are underlaid by
horizontal layers of sedimentary rock.
Plains are broad areas of level land, such as the great plains
region of central North America.
Lowlands are plains located along coastlines , for example,
the Great Lakes – St. Lawrence Lowlands