Transcript Introduction to Plate Tectonic Theory

Introduction to Plate Tectonic
Theory
Introduction
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Plate tectonics is the theory that Earth's outer
layer is made up of plates, which have moved
throughout Earth's history.
The theory explains the how and why behind
mountains, volcanoes, and earthquakes.
Pangaea
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225 million years ago, all the major continents
formed one giant supercontinent, called
Pangaea.
Initiated by heat building up underneath the
continent, Pangaea began to split apart, around
200 million years ago. These continents are still
on the move today.
Theories of Plate Motion
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Exactly what drives plate
tectonics is not known.
One theory is that convection
within the Earth's mantle
pushes the plates.
Another theory is that gravity is
pulling the older, heavier
ocean floor with more force
than the newer, lighter
seafloor.
Plate Motion
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Plate tectonic activity takes place at four
types of boundaries:
Divergent boundaries
Convergent boundaries
Collisional boundaries
Transform boundaries
Divergent Boundaries
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Also known as spreading boundary, it occurs
where two plates move apart, allowing magma,
to rise from the Earth's interior to fill in the gap.
The two plates move away from each other like
two conveyor belts moving in opposite
directions.
Convergent Boundaries
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Also known as subduction boundary, it occurs
where one plate slides under another as the two
are pushed together.
If there is land at the edge of one of these
plates, the ocean plate will subduct, or slide
under that plate.
Collisional Boundaries
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A collisional boundary
occurs where two
land masses on
plates are pushed
together.
Trying to occupy the
same space, the land
masses buckle and
fold, creating
mountain ranges.
Transform Boundaries
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A transform boundary occurs where two
plates slide against each other.
Rather than sliding smoothly, the plates
build up tension, then release the tension
with a spurt of movement called an
earthquake
Birth of a Theory
video questions
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What led Wegener to his notion of continental
drift?
What is and where does sea floor spreading
occur?
How did paleomagnetism help support the
notion of sea floor spreading?
What is a transform fault?
Why is plate tectonic theory called a “model that
describes everything”?