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Bill Nye – Earth’s Crust
The Cross-Section of Earth
Review: The Cross-Section of Earth
Earth is over 1200 km thick, and has four
distinct layers.
These layers are the crust, mantle (upper
and lower), outer core, and inner core.
Crust
• Outer solid rock layer (granite on land,
basalt in oceans)
Mantle
• Thickest layer, mostly
solid except for upper
mantle being able to
flow like “thick
toothpaste”
Outer core
• Composed of liquid iron and
nickel
Inner core
• Mostly solid iron, at tremendous
temperature and pressure
Earth’s Layers
Review: Earth’s Layers
Tectonic plates make up the
lithosphere, which floats on the
asthenosphere.
Lithosphere
• The crust and upper portion of
the upper mantle.
Asthenosphere
• The molten layer of the upper mantle.
• Heat to keep asthenosphere molten comes from radioactive
elements.
• A convection current forms as hot, low density rock rises
Convection Current (Mantle Convection)
Review: Convection Current
Continents, attached to the
tectonic plates, float in the magma
of the asthenosphere.
As magma is heated in the
asthenosphere, convection currents
form.
Rising magma can reach the
surface at ridges (in the oceans) or
rifts (on land).
The magma cools when it reaches the surface, solidifies, and is pushed
aside as new magma pushes from below. This is called ridge push.
Pangaea Puzzle
Evidence for Continental Drift
Early maps of the world caused Wegener to
continental drift theory
propose the _______________________
because the continents looked as though they
fit together like ______________.
puzzle pieces
might _____
The continental shelves actually fit together
even better. This original supercontinent was
Pangaea
called ___________.
Wegener also realized that other evidence
also supported his theory.
geologic features
• There were matching __________________
and _______
rocks on different continents.
Like pieces of a jigsaw
puzzle, the continents fit
together into one, large
whole.
mountain
• It could help explain why ___________
ranges that begin on one continent,
________
end at the coastline, and then appear to
continue on a continent across an ocean.
http://geography.howstuffwo
rks.com/terms-andassociations/pangaeasupercontinent.htm/printable
fossils on different continents.
• There were matching ________
• There was evidence of different
__________
climates (e.g. glaciers) on
warm continents.
Glaciers vast masses of _____
ice
_________:
• Now found at the _______
poles and
high in the mountains
• Used to cover large areas of
_______
land during __________
ice ages
• When they __________
advance or
_________,
they _______
retreat
mark the
land, leaving behind large, Ushaped valleys, deeply scratched
rocks, and various types of
patterns of rock formations
How Can Continents Move?
Wegener’s evidence for continental drift didn’t explain how entire
continents could change ___________.
locations
New scientific equipment allowed scientists to measure the _______,
slow
but ________,
steady _______
drift of Earth’s _______________.
tectonic plates
It was noted that ______________
earthquakes and ___________
volcanoes appear in
certain patterns, which happen to be along the edges of tectonic
plates.
Volcanoes are frequently
boundaries
found on _____________
between tectonic
plates.
Earthquakes and ___________
volcanoes are __________
dramatic events, where
_____________
earthquake is a ________,
sudden _________
release of built-up ________
energy at or under
surface whereas volcanoes are __________
openings in Earth’s surface
Earth’s _________
that spew out _______,
gases chunks of ______,
rock and melted rock when active.
ocean floor revealed
Mapping of the ____________
the __________________,
MidMid-Atlantic Ridge a long
mountain range running down the
middle of the ________________.
Atlantic Ocean
________
Rocks taken from the
Mid Atlantic ridge were
younger than other
_________
ocean rocks.
Sediments along the Ridge
became _________
thicker further
away from the ridge.
magnetic field
liquid iron
Earth’s ________________
is produced by the motion of ____________
in the planet’s interior. Over time, the ____________
orientation of Earth’s
reversed (“__________________”).
magnetic field gets __________
magnetic reversal
__________________
align with the Earth’s magnetic field
IronIron-based metals in rocks _______
lines, similar to how a compass needle points north.
Paleomagnetism shows that iron-based rocks along the ridges are
_________
striped with reversing magnetic fields.
Sea Floor Spreading: An Explanation
magma rose to form new rock at certain
Hess suggested that _________
places.
melted rock
• Magma (_____________),
rises and falls like warm and cold
liquids.
The ___________________
convection current of magma formed a _________________
spreading ridge
where it broke through Earth’s ______
crust (“new crust” conveyer belt).
__________________
Magnetic striping of basalt rock shows long stripes of ______
new
rock ______________
moving away from ocean ridges, and also reveals the
direction of Earth’s magnetic field at that time.
hot spots are anywhere __________
magma rises to Earth’s
Geologic ___________
surface.
Wilson then unified the ideas of Wegener and Hess into the plate
tectonic theory. He explained continental drift occurs because of
areas like these ridges, that _______
push along ________________
tectonic plates
floating on Earth’s surface.
Figure 21 - Hawaiian hot spot volcanism, displaying the tell-tale track of volcanoes which grow older away
from current active volcanoes. These volcano tracks indicate that the lithospheric plate is moving over a
stationary mantle plume.
Plate Interactions
A plate boundary is where
contact
two plates are in _________.
The way the plates interact is
based on the type of plate,
and the direction the plates
are moving relative to each
other.
Tectonic plate boundaries, and their relative
movement to each other.
Divergent plate boundaries
1. ___________
spreading apart
• Plates are ________________
ridges and
• E.g. Ocean _______
rifts
continental ______
MidMid-Atlantic Ridge is the
• The ___________________
mountain range on Earth
longest __________
Divergent Plate Boundaries (Mechanism)
Divergent Plate Boundaries (Examples)
Tectonic plates
_______________
are all moving at the
same time.
There are 12 large
tectonic plates, and
many smaller ones.
Where continental and
oceanic plates meet,
subduction occurs.
____________
dense oceanic plate subducts under the ________
lighter
• More ________
continental plate.
slab pull
• By “__________”,
the rest of the plate follows.
volcanoes are found in subduction
earthquakes and ___________
• Large _____________
zones.
Convergent Plate boundaries
2. _____________
meet and ________
collide
• Plates _______
3 Types:
OceanicOceanic-Continental plate convergence
i) ___________________
The oceanic plate __________
subducts under the
trench
continental plate, forming a ________.
Cone-shaped ___________
volcanoes can form from magma
seeping to the surface.
• This is how the _____________
volcanic belt of the Pacific
Northwest has formed.
Coast Mountain
Mountain ranges like the ________________
range also form from the collision.
_______
Earthquakes can occur when subduction,
ridge push and slab pull stall.
Oceanic-Continental Convergent Plate Boundaries
(Mechanism)
Oceanic-Continental Convergent Plate Boundaries
(Examples)
Coast Mountains of
British Columbia
OceanicOceanic-Oceanic plate convergence
ii) _________________
cooler _____________
more dense
The ________,
plate (older crust) will subduct
under the other.
Convergence may produce a
volcanic island arc such
__________________,
as those found in Japan,
Indonesia and Alaska’s
Aleutian islands
_________________.
Oceanic-Oceanic Convergent Plate Boundaries
(Mechanism)
Oceanic-Oceanic Convergent Plate Boundaries
(Example)
Aleutian Island of
Alaska in U.S.
ContinentalContinental-Continental plate convergence
iii) _______________________
Since both are continental
densities are
plates, __________
equal
________.
fold
As they collide, edges ______
and crumple, forming
mountain ranges.
Himalayas are the world’s youngest (and tallest)
E.g. The ____________
mountain range.
• They formed as _______
Asia and
Africa plates collided 40
________
million years ago.
taller
• They are still growing _______
today.
Continental-Continental Convergent Plate Boundaries
(Mechanism)
Continental-Continental Convergent Plate Boundaries
(Examples)
Himalayas
3. ___________
Transform plate boundaries
move past each other horizontally
• Plates ___________
ocean ridges
• Usually are found near ______________
slides past rock in these boundaries,
• Since rock ________
NO
earthquakes and _________
faults are very common, but _____
_____________
mountains or volcanoes will be formed
Transform Plate Boundaries (Mechanism and Example)
Overall Summary
Earthquake Video
Earthquakes
Earthquakes often form from the
friction between moving
_________
tectonic plates. This accounts for
95% of all earthquakes.
Pakistan
Earthquakes are very difficult to
predict
_________.
Scientists understand
why they happen, but it is very
timing
difficult to predict their ________,
exact _________
location and _________.
strength
• Their build-up happens
underground over very
_____________,
long periods of time.
• What we do understand has
structures
helped prepare ___________
to survive them.
San Francisco
Earthquakes (Mechanism)
The ________
focus of the earthquake is the location inside Earth where an
starts This is where _________
energy and __________
pressure get
earthquake ________.
released
__________.
epicenter is the point on
The ___________
directly above the
the surface ______________
focus.
Waves of Energy travel
outwards from the focus
of an earthquake.
Example
Juan de Fuca convergent plate boundary west of Vancouver
The ______________
earthquakes Large earthquakes hit this region
Island has many _____________.
every 200 - 800 years.
Earthquakes occur at various _________,
depths depending on the type of
tectonic plate interaction plates involved.
Earthquakes at the _________
surface tend to cause _______________.
more damage
energy of an earthquake is
Seismic waves form when the ________
_______________
released.
Seismology is the study of these waves.
____________
source and _________
• These waves reveal the ________
strength of an
earthquake.
composition and __________
distances
• They also help us learn about the ____________
of the Earth’s interior.
Seismic waves behave ___________
differently in different Earth layers.
• The movement of waves through Earth’s interior is affected by the
density and depth of the different layers
composition (________)
• Knowing this, scientists can learn much about both earthquakes
and the ________
interior of Earth.
Note: S-waves disappear at the bottom of the mantle because they cannot
liquid outer core.
travel through the _______
______________
Seismometers are used to measure seismic wave energy.
• Records the ___________
vibrations
from earthquakes
• Early seismometers just
ground
measured if the ________
shook or not.
• Some seismometers
measure horizontal
movement, others vertical
movement.
seismogram is produced,
A _____________
showing when an earthquake
started, how long it lasted, and
magnitude
the ____________.
___
1 in magnitude = ______
10X stronger
100X more powerful than a 4.
E.g. A magnitude 6 earthquake is _______
Since seismic waves travel at different ________,
speeds a distance-time
graph, revealing the focus.
Bill Nye: Volcanoes
Volcanoes
The movement of tectonic plates causes volcano formation
Composite volcanoes - this is the stereotypical volcano,
1. ___________
smoke and ______
ash everywhere, found
erupting and belching _________
plate boundaries
along ________________.
Layers of ash and thick ______
lava (magma outside Earth) form
cone
a tall ______.
magma reaches the surface, it _______,
cools __________
hardens
As _________
gases below.
and traps _______
Pressure builds, eventually there is an ___________.
eruption
__________
Mount St. Helens, Washington
Shield volcanoes - these are NOT found at plate boundaries,
2. ________
but instead form over hot spots (a weak spot in the normal
lithosphere).
hot spot and forms a
Thin magma/lava flows out from a __________
_____
low , wide _______.
cone
The _________________
Hawaiian Islands are an example of a chain of shield
volcanoes.
Yellowstone National Park
cracks in the
3. ______________
Rift eruptions - these occur along long ________
lithosphere
_____________
massive amounts of
These are NOT explosive, but release _________
lava
______.
Ridges are due to rift eruptions
under the ocean.
The Krafla volcano,
Northern Iceland