Transcript Earth`s Movement - Book Units Teacher

Earth’s Movement
Plate Tectonics and Faults
Pangaea
Approximately 200 million years ago
Earth's land was grouped together in
one large super-continent named
Pangaea.
http://pubs.usgs.gov/gip/dynamic/historical.html
Jurassic & Cretaceous Periods
Pangaea began to break apart during
the Jurassic Period.
http://pubs.usgs.gov/gip/dynamic/historical.html
Present Day
http://pubs.usgs.gov/gip/dynamic/historical.html
Notice the shape of South America
and Africa. Can you picture how
these two land masses fit together
like a puzzle?
Evidence
Scientists have found evidence that
the continents are moving in fossils.
For example, fossils of tropical plants
were found in Antarctica which led to
the conclusion that this frozen land
had previously been closer to the
equator.
Fossil Evidence
http://pubs.usgs.gov/gip/dynamic/continents.html
Plate Tectonics
Plate Tectonics is a theory that was
developed in the 1960's. This theory
states that Earth's top layer called
the crust is divided into plates that
are moving at a speed of 1 to 10 cm
per year.
Tectonic Plates
http://pubs.usgs.gov/gip/dynamic/slabs.html
Another Picture of the
Tectonic Plates
Fault
The breaks in the Earth’s crust where
the plates meet (push together, pull
apart, and slide beside each other)
are called faults.
Plate Movement
The plates move in three ways:
 Divergent
Plate Movement ← →
 Convergent
 Transform
Plate Movement → ←
Plate Movement or
Lateral Slipping Plate Movement ↓↑
Divergent Plate Movement ← →
Convergent Plate Movement → ←
Transform Plate Movement
or
Lateral Slipping Plate Movement ↓↑
Mid-Ocean Ridges
Mid-Ocean Ridges are places where
the Earth's tectonic plates are
gradually moving apart. As the
plates move apart, magma rises up
to fill the gap. This can cause
undersea volcanic eruptions.
This shallow magma provides a heat
source that creates many seafloor
hot springs along the ridges which
transport heat and chemicals into the
ocean.
Mid-Ocean Ridge
http://pubs.usgs.gov/gip/dynamic/baseball.html
Activity
You will be given a piece of waxed
paper. On the wax paper spread a
spoonful of icing about a half of a
centimeter thick. The icing
represents the magma that is
under the Earth’s crust. Next you
will be given two squares of fruit
rollups. Place the two squares of
fruit rollup onto the frosting right
next to each other. These
represent oceanic plates. Press
down slowly on the fruit rollups
because oceanic plates are dense
and will sink a bit. Slowly push the
“plates” apart about half a
centimeter. Notice how the frosting
is exposed and pushed up where
the plates are separated. This is
how magma comes to the surface
where real plates are moving apart
at divergent plate boundaries.
Volcanic Activity
The black
dots
represent
volcanic
activity.
Notice that
most of
these are
along the
edges of
the plates.
These are
called fault
lines.
http://pubs.usgs.gov/gip/dynamic/zones.html
Earth Gains New Crust
On divergent plate boundaries new
crust is being formed as magma
escapes from the Earth's core. In
other locations under the ocean are
deep trenches.
Earth Loses Old Crust
Scientist believe these deep trenches
are where the old crust is being
lowered back into the Earth’s core.
This cycle is known as the Wilson
Cycle, named after John Tuzo
Wilson.
Wilson Cycle
The cycle, beginning with new crust
being formed to the old crust
returning to the Earth's core, takes
approximately 100 million years.
Continents do not fall back into the
Earth's core, so land masses are
much older than the Earth’s crust
beneath the ocean.
Points to Remember
When plates move apart, volcanoes
may form.
←
→
← Divergent →
2 Oceanic Plates
 Submarine mountain ranges
 Volcanic activity
 Earthquakes
 New seafloor
2 Continental Plates
 Rift valley
 Earthquake activity
 Volcanic activity sometimes occurs
Convergent Plate Movement → ←
Convergent boundaries are where
plates are moving toward each other.
The outcome of convergent plate
movement varies depending on the
types of plates that meet:
– Oceanic–Oceanic
– Oceanic-Continental (Land)
– Continental-Continental or (Land-Land)
Vocabulary
Lithosphere - outermost layer of the
earth's crust & is broken up into large
solid plates called tectonic plates - about
40 - 250 miles deep
 Asthenosphere - part of the earth just
below the lithosphere - not liquid but
there is a small amount of melted rock
there - 250 - 435 miles thick
 Subduction - the process that takes place
at convergent boundaries → ← in which
one tectonic plate moves under the other

Oceanic-Oceanic Convergence
When two oceanic plates collide, one is
pushed under the other and magma
from the mantle rises, forming
volcanoes.
http://pubs.usgs.gov/gip/dynamic/understanding.html
Lava Flow
In some cases the magma calmly
erupts. The lava emerges and cools
forming new crust.
Violent Eruption
In other cases the volcano erupts
violently sending dust and ash into
the sky.
Calderas
In other cases the area above the
volcano has cracks which release
gases usually during a volcanic
eruption. As the gases release the
emptied chamber can no longer
support the weight of the earth
above it. The earth falls into this void
leaving deep craters called calderas.
Crater Lake
One famous example of a caldera is North
America’s Crater Lake located in Southern
Oregon. Around 7,000 years ago a
massive volcanic peak reaching 12,000
feet in elevation set in this location. A
powerful eruption blasted the top 4,000
feet away, leaving a deep bowl shaped
caldera. Since that
time, a new dome
has begun to form in
the center of
the caldera.
The factor that determines the type of
eruption is the amount of silica that
is in the lava. Silica is a very
common mineral composed of silicon
and oxygen (SiO2). Silicates makes
up about 95% of the Earth’s crust.
Volcanoes rarely change the type of
eruption that occurs.
Slide the two
pieces of fruit
rollups together.
Notice that one
piece slides under
the other. A hump
forms where the
two pieces hit.
Volcanic mountain
building occurs
when two oceanic
plates meet.
Activity
Oceanic-Continental Convergence
When an oceanic plate pushes against
a continental plate, the oceanic plate
moves under the continental plate.
http://pubs.usgs.gov/gip/dynamic/understanding.html
Activity
Remove one of the fruit rollups
from the frosting. (You may
eat it.) Place one of the
graham cracker halves lightly
onto the frosting next to the
remaining fruit rollup piece.
The graham cracker
represents the continental
crust, which is thicker and less
dense than oceanic crust (fruit
rollup). It floats high on the
asthenosphere (upper mantle
of the Earth) so don't push it
down. Gently push the
continent (graham cracker)
towards the ocean plate (fruit
rollup) until the two overlap,
and the graham cracker is on
top. The oceanic plate is
subducted below the
continental one.
When an oceanic plate meets a
continental (land) plate usually an
oceanic trench will develop on the
ocean side and a mountain range on
the continental side.
Continental-Continental
Convergence
When two continental plates collide,
mountain ranges are created as the
crust is pushed upwards. You can feel
this movement through earthquakes.
http://pubs.usgs.gov/gip/dynamic/understanding.html
Activity
Remove both the cracker
and fruit roll up from the
frosting asthenosphere.
Place one edge of both
crackers into the glass of
water for just a few
seconds. Place the
crackers onto the frosting
with wet edges next to
each other. Slowly push
the graham crackers
towards each other.
Notice how the wet edges
crumple. This is how
mountains are made at
convergent plate
boundaries! When
continents move towards
each other there is
nowhere for the rock to
go but up!
Point to Remember
When two plates move towards each
other mountains form.
→
←
→ Convergent ←
Oceanic and Continental Plates
 Earthquake activity
 Sometimes ocean trench
 Volcanoes
 Destruction of oceanic lithosphere
2 Oceanic Plates
 Earthquakes
 Oceanic trench
 Destruction of oceanic lithosphere
2 Continental Plates
 Folding and faulting
 Mountain ranges
 Earthquake activity
 Shortening of plates
Transform Plate Movement or
Lateral Slipping Plate Movement
↓↑
When two plates move sideways
against each other, there is a
tremendous amount of friction which
makes the movement jerky. This is
known as an earthquake.
Activity


Pick the two crackers up off the
frosting and turn them around so that
two dry edges are next to each other.
Push one cracker past the other to
simulate a transform plate boundary
like the San Andreas fault!
Point to Remember
When two plates move past each other
earthquakes are likely to happen.
↓
↑
↓Transform Boundary↑
 Recurring
earthquake activity
 Volcanic activity
Review
 Divergent
Plate Movement ← →
 Convergent
 Transform
Plate Movement → ←
Plate Movement or Lateral
Slipping Plate Movement ↓↑
http://pubs.usgs.gov/gip/dynamic/Vigil.html
http://pubs.usgs.gov/gip/dynamic/world_map.html
Ring of Fire
The Ring of Fire is a chain of volcanoes and
oceanic trenches. Seventy-five percent of
Earth’s volcanoes are in the Ring of Fire.
http://pubs.usgs.gov/gip/dynamic/fire.html
http://pubs.usgs.gov/gip/dynamic/Farallon.html