Plate Tectonics
Hi,
I am Zed and I am
going to take you on
a trip learning about
Plate Tectonics
And I am
Buddy…Zed’s
mascot
Continental Drift
• Alfred Wegener – proposed that
continents were not always where they are
now – called it continental drift.
• Evidence:
– Fossils
– Landforms
– Climate
Plate Tectonics Comic Book
Page 2
• Wegener’s hypothesis was rejected
because he couldn’t explain how it
happened.
• That evidence was found in 1947 when
scientists discovered the mid-ocean ridge.
Plate Tectonics Comic Book
Page 2
Mid-ocean Ridges
• Undersea mountain ranges that encircle
the globe (like stitches on a baseball).
• New crust is formed at the ridges.
• Sea-floor crust is very young and the crust
closest to the ridges is the youngest.
Plate Tectonics Comic Book
Page 3
Sea-floor spreading
• In the 1950’s scientists started to believe
that the mid-ocean ridges were pushing
the crust apart.
• New crust forms at the ridge and is
pushed away from the ridge – the seafloor is spreading
Plate Tectonics Comic Book
Page 4
• We cannot see it spread.
• Evidence for sea-floor spreading:
– Rocks closest to the ridge are younger than
those further away.
– Paleomagnetism
Plate Tectonics Comic
Book Page 4
Paleomagnetism
• When new crust cools quickly – the magnetic
pieces in them line up and point north.
• Every 70 million years or so, the magnetic poles
reverse – north is south and south is north.
• This can be seen inside of rocks
Plate Tectonics Comic
Book Page 5
• The crust on either side of the mid-ocean ridges
shows patterns of magnetic reversals.
• These patterns show that the sea-floor is
spreading.
Plate Tectonics Comic
Book Page 5
Plate Tectonics part 2
How continents move.
• The continents sit on top of pieces of the
lithosphere.
• The lithosphere sits on top of the
asthenosphere.
• The asthenosphere is hot and soft and
moves slowly, like putty.
Plate Tectonics Comic Book
Page 6
• The chunks of the lithosphere (plates)
move around on top of this soft, hot layer.
• Plates can be made of oceanic crust,
continental crust, or both.
• Oceanic crust is more dense than
continental crust.
Plate Tectonics Comic Book
Page 6
Plate contact
• Anywhere one plate touches another there
are usually earthquakes and volcanoes.
• All of the plates are in motion.
Plate Tectonics
Comic Book
Pages 6-7
Plate boundaries
• Plate boundaries are the places that plates
touch.
• There are 3 types:
– Convergent – Where plates push towards
each other.
– Divergent – Where plates are moving away
from each other.
– Transform – Where they are sliding past each
other
Plate Tectonics Comic Book
Page 7
Plate Boundaries
Plate Tectonics Comic Book
Page 7
Why do the plates move?
• Convection – When a liquid or a gas is
heated it becomes less dense.
– The cooler and more dense material sinks.
– This pushes aside the hot material and it
rises.
– This sets up convection currents.
Plate Tectonics Comic Book
Page 8
• There are convection currents in mantle.
• Heat from the core drives these
convection currents.
• These currents drag the plates above
them.
Plate Tectonics Comic Book
Page 8
Plate Tectonics Notes
Part 3
Effects of continental change
• As continents move their climate can
change.
– Ex. Parts of Antarctica used to be covered
with jungle.
• Living organisms change as well.
– When a population is separated it can evolve
differently until they are no longer the same
species.
Plate Tectonics Comic Book
Page 9
Supercontinent
• A supercontinent is when most of the
earth’s landmasses are attached.
• Pangaea was the last supercontinent.
• It broke apart and continents that were
once attached are moving apart.
• In about 250 million years a new
supercontinent might form.
Plate Tectonics Comic Book
Page 10
Rock Stress
• Rocks can be changed as pressure is
added in different ways.
• Compression is when rocks are pushed
together.
– This can cause rocks to fold or crack.
– Happens mostly at convergent boundaries.
Plate Tectonics Comic Book
Page 11
• Tension happens where rocks are being
pulled away from each other.
– Mainly happens at divergent boundaries.
– Rocks can become thinner or crack.
Plate Tectonics Comic Book
Page 11
• Shear stress – when rocks are being
pushed in opposite directions (sideways)
– Happens mainly at transform boundaries
– Causes rocks to twist, bend, or break.
Plate Tectonics Comic Book
Page 11
Mountains
• Mountains are formed mainly by the
collision of 2 plates.
• When oceanic crust meets continental
crust the continental crust is pushed.
• The oceanic crust sinks underneath and
melts forming volcanoes.
Plate Tectonics Comic Book
Page 12
• When two oceanic plates collide, the more
dense one sinks below the other.
• As it sinks, it melts to form volcanoes.
• Examples are Japan and Hawaii
Plate Tectonics Comic Book
Page 12
• When two continents collide, the crust is
pushed upwards.
• The Himalayas were formed this way
when India ran into Asia. (still growing)
• Some crust may also sink and melt
forming volcanoes.
Plate Tectonics Comic Book
Page 12
Types of Mountains
• Folded Mountains
– Highest mountain ranges in the world
– Tectonic plates colliding squeeze rock layers
upward, folding and faulting them
– Himalayas, Appalachians, Alps are examples
Plate Tectonics Comic Book
Page 13
Types of Mountains
• Fault-Block Mountains
– Crust has been stretched and broken into
large blocks
– Happens where plates are being pulled apart
– Sierras, Wasatch, and Teton’s are examples
Plate Tectonics Comic Book
Page 13
Wasatch
Mountains in Utah
County
•
•
Fault Block Mountains
Provided by:
Sandy Gertsch, Utah County, Utah, School System
•
Thirty miles south of Salt Lake City, near the mouth of Provo Canyon in Orem, Utah
is an excellent example of fault block mountains. The north-south trending Wasatch
Range extends throughout the center of Utah. The western flank of the range is very
steep and relatively straight, the result of displacement along the extensive and stillactive Wasatch Fault. Summits along the crest of the range have elevations between
9,000 and 10,000 feet. The mountain-sized fault blocks of this region developed in a
fairly orderly fashion, breaking roughly at right angles to the westward direction of
stress. As visible in this photo, the truncated spurs of the Wasatch Mountains provide
evidence that movement on the Wasatch fault is geologically recent. Utah lays claim
to many thousands of faults, large and small. Mountains have been formed by normal
faults, reverse faults, thrust faults and extension or detachment faults. The valley held
an arm of Lake Bonneville, a lake that formerly covered this area 25,000 years ago in
the Pleistocene era. This lake varied in level over the years and left clearly seen
shorelines, benches, ridges and gravel bars. The slope on the left of this picture is an
example of this ancient deposition.
Types of Mountains
• Domed Mountains
– Rare type formed when magma rises and
pushes up against the surface without
breaking through
– A rounded mountain with a center peak
– Henry Mts. In Utah, Black Hills of S.D. are
examples
Henry Mountains In Utah
Plate Tectonics Comic Book
Page 13
Salt Domed Mountain
• Astronaut view of domed mountain created when salt,
underlain with petroleum deposits was squeezed up
through more dense rock layers towards the surface.
The End ?????