Exploring the Theory of Continental Drift
Notes Template for Wegener Video & 12.1
Name: _______________________________________
Directions:
Watch the Wegener video in class, read chapter 12 section 1 and fill in the columns with: evidence to support the theory
(column 1), failings of the original theory (column 2), physical results of plate movement (column 3), and the causes of plate
movement (column 4). Use bullets and/or obvious spaces to neatly separate each entry in your columns.
Evidence to Support
Failings of the Original Theory
Continental Drift
of Continental Drift
 northwestern coast of
 If continents left a
Africa fits nicely with
wake, it would be a
the coast of the eastern
huge obvious wall of
US
water- there is no wake
 the southern tips of
 Wegener could not
south America and
explain a mechanism
Africa seem to fit into
for movement- he
the Weddell Sea of
guessed that is was
Antarctica
caused by gravitational
pull of sun & moon and
 edges of continental
centrifugal forceshelves of Africa and
physicists showed that
the Americas were
combining these forces
shown to match very
would not be enough
well by oceanographers
 Geologists argued that
 animals found on more
continents could not
than one separated
“push thru the ocean
continent: mesosaurus,
floor b/c the rock of the
cynognathus,
ocean floor is too rigidlystrosaurus, and a
Results of Plate Movement



mid-ocean ridge (MOR) &
sea floor spreading- magma
from mantle is forced up
due to its low density, it
cracks the oceanic crust and
causes it to move apart,
causing a mountain range on
both sides with a rift valley
between
divergent plate movement
leads to mountain ranges
with rift valleys as in East
Africa between the African
plate and the Arabian plate
convergent plate movement
in which the more dense
plate is subducted creating a
mountain range with
volcanic arches (as the heat
in the subduction zone melts
rock and produces magma)
and a deep sea trench on
the opposite side- like the
Causes of Plate Movement



Ridge push at the MORdivergent boundaries
are higher at the center
of the ridge, gravity
forces material down
the slopes of the MOR
Slab pull at subduction
zones where portions
of the descending plate
pull the rest of the
plate with them- like
when covers on your
bed are pulled off due
to gravity
Friction between plate
and the mantle is
greater beneath
continental crust than
oceanic crust- so




plant: glossopteris
mountain ranges
matched up when
continents were joined
and they shared the
same rocks/ minerals
midocean ridges &
other evidence of
seafloor spreading
mapped out by Dr.
Harry Hess’s sonar
samples of rock
material near
continents are older
than near MORs- so
new rock or magma
must be created at the
MOR and it moves
away over time, aging
(proves movement)
bands of rocks lined up
to show reversal of
earth’s polarity are
found both on the sea
floor and on mountain
ranges
thus the rock would
break or fracture, and
there is no evidence of
this




Andes Mtn range
when oceanic crusts collide,
magma is released to create
volcanic islands called island
arcs- like Japan
earthquakes (and tsunamis)
occur especially along
convergent boundaries
if subduction does not occur
@ a convergent boundary,
the crust buckles upward to
form high folded mtn ranges
without volcanic arches- like
the Himalayas
transform boundaries
indicate horizontal
movement where no new
rock is formed and no old
rock is recycled- allow
movement away from the
MOR

continental plates are
noticeably slower
moving than oceanic
plates
Internal convection
inside the earth driven
by radioactive heat,
pressure & friction