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9.3 & 4: Theory of Plate Tectonics
lithosphere forms the thin outer shell of
Earth and is broken into several pieces
called plates
asthenosphere: solid, plastic layer of the
mantle beneath the lithosphere
made of mantle rock that flows very
slowly which allows plates to move on
top of it
plate tectonics: theory that explains
how large pieces of the lithosphere
(plates) move and change shape
plates ride on the asthenosphere like
blocks of wood float on water
continents and oceans are carried
along on the moving plates like
passengers are carried by a bus
plates can include continental crust,
oceanic crust, or both
scientists have identified about 15 major
plates
boundaries of the plates do not always
match the outlines of continents
plate boundaries may be in the middle of
the ocean floor, around the edges or
within continents
three types of plate boundaries are
divergent, convergent, & transform
fault
each plate boundary has a
characteristic type of geologic activity
Chapter 10
divergent: where plates move apart
area where new crust forms
usually found on the ocean floor
can also create volcanoes
Chapter 10
convergent: where plates run into
one another (come together)
three types of convergent
boundaries based upon types of
plates that are colliding
Chapter
10
ocean/continental
= ocean crust (is
denser) is pushed down into the
mantle, creating a trench
can also make a range of volcanic
mountains called a continental
volcanic arc
due to
melting of
the ocean
plate in the
mantle
Chapter 10
ocean/ocean = one is pushed down
into the mantle creating a trench
can also make a range of volcanic
mountains that are in the ocean so
are called a volcanic island arc
Chapter 10
continental/continental = both are
pushed up creating a mountain
range
Chapter 10
transform
fault: plates grind past
each other
causes earthquakes
How Does This Happen?
convention currents in the mantle
are the driving force behind plate
movements