Transcript Notes for plate tectonics unit

Plate Tectonics Unit:
Composition of the Earth:
Layers of the Earth:
1. Crust: 5-100km thick.
a. Oceanic crust: thin and
more dense, mostly
basalt
b. Continental crust:
thicker and less dense,
made up of more
granite than oceanic
crust
Layers, Continued:
2. mantle: made of molten
(melted rock), very thick,
2,900 km, and likely to
have convection currents.
3. Outer Core: molten iron,
2,200 km thick
4. Inner Core: solid but very
hot iron, 1,230 km thick
The core makes up 33% of
Earth’s total mass
Tectonic Plates:
Because of convection
currents in the mantle,
plates of the earth’s crust
move around as they “float”
on the mantle. Over many
millions of years, the
location of the oceans and
continents have changed
dramatically, and surface
features like valleys and
mountain ranges are
continually created and
destroyed.
Wegener’s Theory of Continental Drift:
In 1910, a German
scientist named Alfred
Wegener proposed that
the continents had, in the
very distant past, been
joined together in one
supercontinent he called
Pangea, and had since
drifted apart into separate
continents. He called this
theory Continental Drift.
Wegener’s arguments in support of his theory:
1. Evidence from landforms:
• Continents along the Atlantic Ocean appear to
fit together like puzzle pieces.
• Mountain ranges in South Africa match up
with mountains in South America.
• Coal deposits in Europe match up with coal
deposits in North America.
2. Evidence from fossils:
• Fossils of the same species of land animals and land
plants had been found on different continents; they
could not have crossed oceans.
• Fossils of tropical plants were found on the island of
Spitsbergen, which is well north of the Arctic Circle.
Wegner proposed that this island had once been close
to the equator.
• Evidence of glaciers had been found in South Africa,
which currently has a subtropical climate. Wegner
thought South Africa must have been much farther
south millions of years ago.
Unfortunately, no one
believed Wegener at the
time. His evidence was
not totally convincing, and
he could not explain what
force could cause whole
continents to move.
Plate Tectonics: Wegener was Right!
Starting in the 1960’s, as
scientists started mapping
the ocean floor, they
discovered that the ocean
floor was spreading out
along the Mid-Ocean
Ridge. This very easily
explained how continents
could move.
How Sea-Floor Spreading Works:
Evidence for Sea-Floor Spreading:
1.
2.
3.
Rock samples from the ocean
floor close to the mid-ocean
ridge are younger than rock
samples farther away.
Magma can actually be
observed oozing up from the
mid-ocean ridge, and cooling
into rock.
Iron samples from the ocean
floor alternate their patterns,
showing that some parts of
the ocean floor were formed
at times when the magnetic
poles were reversed.
Subduction at Deep Ocean Trenches:
The Ultimate Cause of Plate
Movement? Convection!
Tectonic Plates of the Earth:
Homework:
LO: Describe the theory of plate tectonics
SLE: Work independently
1. Read p. 104-111
2. Answer review questions on p. 111
Types of Plate Boundaries:
LO: Describe the theory of plate tectonics
SLE: Meet or exceed NGSS
Checkpoint Quiz on Plate Tectonics:
1. List the layers of the interior of the earth,
starting with the middle and going outwards.
2. How do we know the earth’s core is solid?
3. Give one piece of evidence that the seafloor is
spreading.
4. Give one of Wegener’s arguments in favor of his
theory of continental drift.
5. Describe three types of plate boundaries (OK to
draw diagrams).
LO: Describe the theory of plate tectonics
SLE: Meet or exceed NGSS
Checkpoint Quiz on Plate Tectonics #2:
1. Describe the process of sea-floor spreading.
2. Give one piece of evidence that the sea floor
is spreading.
3. What causes the formation of most mountain
ranges?
4. Name three types of plate boundaries, and
describe the movement of plates along each
one (diagrams OK) (2 points)
The Effects of Tectonic Plate
Movement on Earth’s Surface :
Plate movement causes
the earth’s surface to
deform (noun:
deformation): layers of
rock bend or break
because of the stress
placed on them.
Main Types of Stress:
Compression: When two
plates are squeezed
together.
Tension: When two plates
are pulled apart.
Shearing: when two plates
are pulled past one
another.
Folds:
Folding is the bending of
rock layers due to one of
these three types of stress.
Types of folds:
Anticlines: upward-pointing
folds.
Synclines: Downwardpointing folds.
Monocline: A step-like fold
in which both ends are
horizontal.
Faults:
Faults are regions where
rock areas break and slide
past each other.
When faults are not
totally vertical, the upper
part is called the hanging
wall and the lower part is
called the footwall.
Types of Faults:
Plate Tectonics and Mountain
Formation:
The motion of Earth’s
plates causes mountains
to form, mostly at plate
boundaries.
The type of mountains
that are formed depends
on what type of plate
boundary it is.
Types of mountains:
Folded Mountains: When
plates are squeezed together
and pushed upward. These are
usually formed at convergent
boundaries.
Fault-Block Mountains: When
plates move apart and one
section of rock drops down
relative to other sections.
(These tend to be smaller
mountains.)
Volcanic Mountains: Formed
by volcanic eruptions, usually
near subduction zones.
Homework:
LO: Describe effects of the movement of
tectonic plates.
SLE: Articulate ideas clearly and effectively.
1. Read p. 112-118
2. Answer review questions on p. 119
LO: Describe motion of the earth along faults.
SLE: Meet or exceed NGSS
Checkpoint Quiz on rock movement:
Draw three kinds of faults. For each fault, draw
arrows to show how the earth moves along that
fault. Also mention the type of stress
experienced at each type of fault: (6 points)
1.
2.
3.
Earthquakes:
Where earthquakes occur:
Most earthquakes occur
at or near plate
boundaries. The crust
moves more often in
these places, and stress is
more likely to build up
there.
The cause of earthquakes:
Rock at plate boundaries or along faults will
stretch as sections move past one another, but
eventually so much pressure builds up that the
rock breaks and snaps back (like a rubber band),
which releases waves of energy. The sudden
snapping back of rock is called elastic rebound.
http://wn.com/elastic_rebound_and_earthquak
es
Seismic waves:
Seismic waves are energy waves caused by rock vibrations
along a fault. There are 3 kinds of seismic waves:
1. Primary (P): The first to arrive (the fastest). They
compress and expand like a Slinky.
2. Secondary (S): They come after primary waves. They
move from side to side and up and down. S waves,
unlike P waves, can not travel through liquids.
3. Surface waves: P or S waves that have reached the
surface. These are the waves that cause the most
damage, although they are slower than the other
two.
How earthquake strength is measured:
Earthquakes are detected,
located and their strength
measured by a machine
called a seismometer.
They record the
movement of the earth
using a needle; the more
the ground shakes, the
more the needle does,
too.
Earthquake measuring scales:
1. Mercalli Scale:
Developed early in the
20th century, this scale
does not measure the
energy precisely, but
records the amount of
damage that has been
done.
2. Richter Scale:
Developed in 1930, it
measures the strength of
an earthquake according
to how much motion the
nearest seismometer has
recorded. This could
change depending on how
far away from the
earthquake the
seismometer is.
3. Moment Magnitude
Scale: This is the scale
used today. It measures
the total energy produced
by the earthquake, not
the results of the
earthquake. In this scale,
each magnitude is ten
times larger than the next
lowest number.
Epicenter vs. Focus:
Focus: The location below
ground where the
earthquake begins. This
can be many Km below
the surface.
Epicenter: The first
location on the surface
where the earthquake can
be felt.
Homework:
LO: Describe cause and effects of earthquakes.
SLE: Meet or exceed NGSS.
1. Read p. 130-139
2. Review questions on p. 139
LO: Identify, describe causes and effects of
earthquakes
SLE: Articulate ideas clearly, effectively and creatively.
Earthquake paragraph:
Write a 5-7 sentence paragraph (including topic
sentence) that describes the Cascadia Fault.
Include information about where the fault is
located, what would cause an earthquake at this
fault, and what the effects of a “megathrust”
earthquake might be on cities in the Pacific
Northwest. (No hysteria or fear-mongering,
please.)
LO: Describe the cause and effects of earthquakes.
SLE: Meet or exceed NGSS
Checkpoint Quiz on Earthquakes:
1. Draw diagrams of normal, reverse and strike-slip
faults. For each type of fault, label the foot wall,
hanging wall, and the direction of movement along
the fault.
2. What causes earthquakes?
3. Where on on Earth are earthquakes most likely to
occur?
4. What device is used to measure the amount of energy
produced by earthquakes?
5. What’s the difference between an epicenter and a
focus of an earthquake?
Earthquake Safety:
The likelihood of
experiencing an
earthquake depends on
where you are. If you live
near a plate boundary,
your earthquake hazard
level is higher.
Forecasting Earthquakes:
Predicting when and where the next earthquake
will occur is very difficult. However, scientists
sometimes try the Gap Hypothesis:
Areas along faults that haven’t had an
earthquake in a while are more likely to
experience a strong one in the future.
Earthquake-Proof Building Design Features:
Mass Damper: A weight placed on the
roof to keep the building from swaying.
Shear wall: braces in walls to prevent
them from tearing in half.
Active tendon system: Shock absorbers
built into the frame of the building.
Base isolators: Felxible layers of material
built into the foundation of the building.
Pilings: In soft soil, long posts
underground attached to the bedrock
below the surface.
Cross braces: To keep the building from
shaking apart.
Flexible pipes: To prevent fires from gas
leaks.
What to do during an earthquake:
• Drop, cover and hold
• Wait 100 seconds in
case of immediate
aftershocks
• Quickly and calmly exit
the building
• Gather in an open area
and await instructions
from trusted adults.
Homework:
LO: Identify and describe earthquake-resistant
design features
SLE: Work independently
1. Read p. 140-145
2. Review questions p. 145
LO: Identify and describe earthquake-proof design
features.
SLE: Work collaboratively.
Design and build an earthquake-proof building.
Materials: 100 3 x 5 cards, 1m masking tape, 10 straws.
Rules:
1. You may only use the materials provided.
2. The building must be at least 50cm tall and 20cm
wide.
3. The building must be free-standing.
4. The building must have 4 or more earthquake design
features.
5. It must be able to withstand shaking for 30 seconds.
Volcanoes:
A volcano is a crack or
weak point in the earth’s
crust through which
magma comes near or
onto the surface. (Once
magma reaches the
surface, it’s called lava.)
Magma: below ground
Lava: above ground
Types of volcanic eruptions:
Explosive:
Non-explosive:
Structure of a volcano:
Products of Volcanic Eruptions:
• Lava: the thickness of lava is
determined by the amount of
the mineral silica- the more
silica, the thicker the lava.
• Volcanic ash: dust and small
bits of rock from explosive
eruptions
• Bombs: large rocks
• Lapilli: small rocks
• Gas: mostly CO2, but also toxic
gases
• Pyroclastic flow: an avalanche
of hot gas, ash and dust that
flows down the side of the
volcano at very high speeds.
LO: Model effects of pressure on volcanic eruptions.
SLE: Work Collaboratively
Problem: What effect does increased pressure have on the force of
volcanic eruptions?
Hypothesis:
Procedure:
1. Place 50ml of vinegar in the bottom of a flask with a wider
opening.
2. Add 2-3 tsp of baking soda, and observe what happens.
3. Repeat steps 1-2 with a flask with a narrow opening
4. Compare observations.
Data: Using words or pictures, describe what happens with each
“volcano.” (qualitative data; record observations in words. Diagrams
are OK.)
Conclusion:
Types of Volcanic Landforms:
A volcanic landform is a
feature of the earth’s
surface that is created by
volcanic eruptions. These
include:
• Shield volcanoes
• Cinder cone volcanoes
• Composite volcanoes
• Lava plateaus
• Calderas
Shield Volcanoes:
Shield volcanoes are
created by many layers of
non-explosive (lava-only)
eruptions. They have very
gentle slopes, and can
even be flat, but some of
them are enormous. (The
tallest mountain on earth
is a shield volcano.)
Cinder Cone Volcanoes:
Cinder cone volcanoes
result from small to
medium –sized explosive
eruptions, and are made
almost entirely of ash and
dust (pyroclastic material).
They tend to be small, but
have very steep sides full
of loose material.
Composite Volcanoes:
Composite volcanoes are
formed by alternating
explosive and non-explosive
eruptions. Inside, they have
alternating layers of ash and
lava. They are often
dormant for thousands of
years, but can also produce
extremely large, destructive
explosive eruptions. (All four
of WA’s volcanoes are
composite volcanoes.)
Lava Plateaus:
Lava plateaus are formed
when thin lava flows out
from one or more long
cracks in an area. Over
many thousands or
millions of years, many
layers of lava form a high
flat area (plateau). Some
lava plateaus are gigantic:
the Columbia Plateau in
WA is a lava plateau.
Caldera:
Sometimes, explosive
eruptions are so large and
violent that the entire
magma chamber beneath a
volcano empties out all at
once. With nothing below to
support the weight of an
entire mountain, it collapses
in on itself and forms a
gigantic hole in the ground
called a caldera.
LO: Identify and describe volcanic landforms
SLE: Meet or exceed NGSS
Volcanic Landforms Diagrams:
Create a diagram that describes all 5 of the volcanic
landforms we’ve discussed. For each landform, include:
1. A color diagram of the landform;
2. A caption that describes what kind of eruptions it has;
3. An example –name and location- of that type of
landform (example: Columbia Plateau, Washington
State, USA). Use a laptop to look up the names and
locations of specific volcanic landforms.
Homework:
LO: Identify and describe volcanic landforms.
SLE: Articulate ideas clearly and effectively.
Write a 7-sentence (more is OK) paragraph that
describes each major type of volcanic landform.
Include a description of how each one is formed
and what it looks like.
Causes of Volcanic Eruptions:
Volcanic eruptions are caused
by the movement of volcanic
plates at divergent and
convergent plate boundaries:
1. At Convergent plate
boundaries, rock is affected by
friction between the plates,
which causes the rock to get so
hot it melts. The magma then
reaches the surface via
convection pressures through
weak points in the rock.
The pressure placed on
rocks affects when and
where magma will form.
Rock that is under a lot of
pressure will not melt
even if it is very hot.
When pressure is
released, it becomes less
dense and turns into a
liquid.
2. At divergent plate
boundaries, volcanic
eruptions usually occur
because of lower pressure
instead of higher
temperatures, since
temperature in the upper
mantle is pretty constant.
When plates move apart,
the pressure decreases, the
rock turns into a liquid, and
magma floats to the surface.
Hot Spots:
Sometimes (not often)
volcanoes form in the
middle of plates. Scientists
believe this happens
because bubbles of liquid
rock (magma plumes)
float to the surface
through cracks or weak
spots in the earth’s crust.
Classes of volcanic activity:
1. Active: volcanoes that
have erupted recently,
are erupting now, or are
likely to erupt in the
near future.
2. Dormant: Have erupted
in the distant past, and
are likely to erupt in the
future, but not soon.
3. Extinct: Have not
erupted for a long time
and will not erupt again.
How volcanic eruptions are
predicted:
1. Measuring small earthquakes
near a volcano: if a lot of
small earthquakes, caused by
magma moving through the
crust, are detected, it’s likely
that an eruption will occur.
2. Measuring slope and
temperature: if the surface
on the slope of a volcano
begins to bulge or shift, or if
the temperature near the
crater increases, the chances
of an eruption are greater.
Homework:
LO: Describe how volcanic eruptions occur.
SLE: Meet or exceed NGSS
1. Read p. 166-171
2. Respond to the review questions on p. 171
LO: Describe volcanic landforms.
SLE: Meet or exceed NGSS
Checkpoint quiz on volcanoes:
1. Describe how calderas are formed.
2. Draw a diagram of the inside of a composite
volcano.
3. How does the mineral silica affect volcanic
eruptions?
4. List 2 ways that rock can turn into liquid magma.
5. What is a dormant volcano?
Rocks:
A rock is a naturally
occurring mixture of two
or more minerals. They
can be formed through
the cooling of magma or
lava, under intense heat
or pressure, through the
process of
erosion/deposition, or the
activity of living things.
The rock cycle:
How rocks are classified:
Scientists classify rocks
according to their:
1. Composition: the
minerals they’re made
of.
2. Texture: the size, shape,
and position of the
grains that the rock is
made of.
3. How they were formed
(this is the most general
way to classify rocks).
Homework:
LO: Describe how rocks are classified.
SLE: Meet or exceed NGSS
1. Read p. 28-34
2. Review questions p. 35
Main Types of Rocks:
Igneous: Rock that is formed from cooling magma or lava.
Intrusive igneous rock forms from cooling magma below
the earth’s surface. Because it cools very slowly, it has
coarse-grained texture and large, irregular crystals.
Extrusive igneous rock is formed from lava above the
surface. It cools quickly, so it has small crystals or no
crystals. Its texture depends on its mineral composition.
Sedimentary rock:
Sedimentary rock is formed from sedimenteroded bits of clay, dust, mud or small pebbles
that are pressed together into new rock at or
near the surface. A key feature of sedimentary
rock is that it forms in strata, or layers deposited
on top of one another.
Types of sedimentary rock:
Clastic sedimentary rock: when rock or mineral
fragments are cemented together.
Chemical sedimentary rock: When minerals in
rock crystallize out of a solution (such as sea
water) to form rock.
Organic sedimentary rock: formed from the
remains of dead organisms.
Metamorphic rock:
Metamorphic rock is rock that has been
transformed by heat and/or pressure deep
within the earth’s crust.
Types of metamorphic rock:
Foliated: Crystals or grains are arranged in
orderly, regular bands.
Nonfoliated: Crystals or grains are randomly
arranged.
Homework:
LO: Describe three main classes of rock.
SLE: Meet or exceed academic standards.
1. Read p. 36-49.
2. Complete the review questions on p. 52-53
(Due Monday)