Transcript Plate Tectonics

Plate Tectonics
How the Earth moves
The Definition
• The theory of plate
tectonics states that the
Earth’s lithosphere is
divided into pieces
called tectonic plates
that move around on
top of the
asthensophere
• Plates are either
oceanic or continental
These plates drift very slowly—
centimeters per year
• Once, the world had
one giant
supercontinent, called
Pangea and one giant
ocean.
• Then, over time, the
supercontinent spread
out, forming the 7
continents we know
today—this process is
described as
continental drift
Sea-floor Spreading
• Magma rises from the
mantle and
solidifies—forming
new oceanic
lithosphere.
• Once the magma has
solidified into the
rocky crust, it spreads
out in either direction
Divergent Boundary
• This is the boundary
between two plates
that are spreading
away from one
another
– Like the ones found
where sea-floor
spreading occurs
Mid-Atlantic Ridge: A Divergent
boundary
Convergent Boundary
• A convergent
boundary is formed
where two plates
collide with each other
• Three combinations
exist:
– Continental/continental
– Continental/oceanic
– Oceanic/oceanic
The Three Collisions:
Convergent Boundaries
Transform Boundaries
• A transform
boundary can be
found where two
plates are sliding
past each other
horizontally
– The most famous of
which is the San
Andreas Fault
The San Andreas Fault—A
Transform Boundary
How Mountains Form
Types of Mountains—
Folded
• Folded mountains
form at convergent
boundaries where
plates collide
• Rock squeezes against
rock, pushing it
upward
• These form the highest
mountains in the
world
Types of Mountains—
Fault-Block
• When the crust is
tense, the rock can
break along a series
of faults, causing
large rock blocks to
drop down lower
than other rocks
• Volcanic mountains
form when oceanic
crust sinks into the
asthenosphere by
subduction
• These rock melts,
forming magma
• This magma, under
pressure, eventually
rises and erupts
through volcanic
mountains
Types of Mountains—
Volcanic
The Ring of Fire