Transcript Plate Tetonics Aug 30

Inside the Earth
Composition (What it is made of)
•
•
•
•
Crust (where we live)
Mantle (hot)
Outer Core (even hotter)
Inner Core (HOTTEST)
The Four Layers
The crust is the layer that
you live on and most
widely studied and
understood. The mantle is
much hotter and has the
ABILITY TO FLOW.
The outer core and inner
core are even hotter with
pressures so great you
would be squeezed into a
ball smaller than a marble
if you were able to go to
the center of the Earth!
The Crust
• Outer layer
• 2 types of crust
– Continental (less
dense, made of
granite)
– Oceanic (very
dense, made of
basalt)
The Crust
The CRUST is composed of two rocks. The continental
crust is mostly granite. The oceanic crust is basalt.
Basalt is much denser than the granite. Because of this
the less dense continents ride on the denser oceanic
plates.
Oceanic and Continental Crust
The Lithosphere
The crust and the upper layer of the
mantle together make up a zone of rigid,
brittle rock called the Lithosphere.
The Mantle
• Middle layer
• Very thick layer
The Mantle
The Mantle is the
largest layer of the
Earth. The middle
mantle is composed
of very hot dense rock
that flows like asphalt
under a heavy weight.
The movement of
the middle mantle
(asthenosphere) is
the reason that the
crustal plates of
the Earth move.
The Asthenosphere
The asthenosphere is
the semi-rigid part
of the middle
mantle that flows
like hot asphalt
under a heavy
weight.
The Outer and Inner Core
• Made mostly of iron
• 1/3 of the earth’s mass
• Very hot
Earth’s Layers
• How are the earth’s
layers similar to an
egg?
• Shell=crust
• Egg white=mantle
• Yolk=core
Physical Structure of the Earth
(5 Layers)
• Lithosphere- rigid outer layer (crust)
• Asthenosphere- solid rock that flows slowly
(like hot asphalt)
• Mesosphere- middle layer
• Outer Core- liquid layer
• Inner Core- solid, very dense
Convection Currents
The middle mantle "flows"
because of convection
currents. Convection
currents are caused by the
very hot material at the
deepest part of the mantle
rising, then cooling and
sinking again --repeating
this cycle over and over.
Convection Currents
The next time you heat anything like
soup or water in a pan you can watch
the convection currents move in
the liquid. When the convection
currents flow in the asthenosphere
they also move the crust. The crust
gets a free ride with these currents,
like the cork in this illustration.
Safety Caution: Don’t get your face
too close to the boiling water!
The Outer Core
The core of the Earth
is like a ball of very
hot metals. The
outer core
is so
hot that the metals in
it are all in the liquid
state. The outer core
is composed of the
melted metals of
nickel and iron.
The Inner Core
The inner core of the
Earth has temperatures
and pressures so great
that the metals are
squeezed together and
are not able to move
about like a liquid, but
are forced to vibrate in
place like a solid.
Movie or animation
Plate Tetonics Defined
• Plate tectonics is the theory that the outer
rigid layer of the earth (the lithosphere) is
divided into about a dozen " plates" that
move across the earth's surface relative to
each other, like slabs of ice on a lake
Watch the video NASA Layers of
the Earth
Continents
• Click and drag
• http://www.playkidsgames.com/games/conti
nentNames/default.htm#
Continents
• the continents are merely the crust exposed above sea
level
• the solid surface of the Earth below sea level is also
crust.
• the crust is broken into pieces which are called
"plates."
• The continents are the exposed portions of the Earth's
plates.
• However, some continents may be composed of the
exposed sections of more than one plate. Therefore
"continent" does not equal a plate.
Figure 2. Map showing Earth’s main lithospheric plates and some of the
world’s earthquake occurrences (red dots).
(From http://www.iris.edu/edu/onepagers/Hi-Res/OnePager2.pdf)
Powering the Movement of Plates
• The driving mechanism believed responsible for
plate movement is heat transfer within Earth’s
interior. The source of the intense heat powering
this great task is radioactivity deep within Earth’s
mantle and primordial heat from Earth’s
formation.
The movement of the plates is driven by convection cells in the
mantle so the plates are continuously jostling against each
other. Geologically, the most important things happen at plate
boundaries, including most of the earthquakes, volcanos,
igneous rocks, major metamorphism, and mountain building
processes. Interplate regions tend to be rather boring.
There are three kinds of plate
boundaries
• . Divergent boundaries are where plates
separate from each other, and magma
oozes up from the mantle into the crack
(a fissure volcano) making the ocean
basin wider. This is known as sea floor
spreading.
http://geology.com/nsta/divergent
-plate-boundaries.shtml
• When a divergence occurs within a
continent it is called rifting. Hot magma
rises from deep within the mantle pushing
up the crust and causing pressure forcing
the continent to break and separate. Lava
flows and earthquakes would be seen.
Sea Floor Spreading
• Watch Bill Nye Video on disk
•
Convergent boundaries are where plates
come together, but to do so one of the plates
must dive below the surface into the mantle
along a subduction zone. Convergent
boundaries produce mountain chains of very
large, explosive volcanos (composite type).
• Here crust is destroyed and recycled back into the
interior of the Earth as one plate dives under
another. These are known as Subduction Zones mountains and volcanoes are often found where
plates converge. There are 3 types of convergent
boundaries: Oceanic-Continental Convergence;
Oceanic-Oceanic Convergence; and ContinentalContinental Convergence.
Oceanic-Continental
Convergence
• When an oceanic plate pushes into and subducts
under a continental plate, the overriding
continental plate is lifted up and a mountain range
is created. Even though the oceanic plate as a
whole sinks smoothly and continuously into the
subduction trench, the deepest part of the
subducting plate breaks into smaller pieces. These
smaller pieces become locked in place for long
periods of time before moving suddenly and
generating large earthquakes. Such earthquakes
are often accompanied by uplift of the land by as
much as a few meters.
Oceanic-Oceanic Convergence
• When two oceanic plates converge one is usually
subducted under the other and in the process a
deep oceanic trench is formed. The Marianas
Trench, for example, is a deep trench created as
the result of the Phillipine Plate subducting under
the Pacific Plate.
Oceanic-oceanic plate convergence also results in
the formation of undersea volcanoes. Over
millions of years, however, the erupted lava and
volcanic debris pile up on the ocean floor until a
submarine volcano rises above sea level to form
an island volcano. Such volcanoes are typically
strung out in chains called island arcs.
Continental-Continental
Convergence
• When two continents meet head-on, neither is
subducted because the continental rocks are
relatively light and, like two colliding icebergs,
resist downward motion. Instead, the crust tends to
buckle and be pushed upward or sideways. The
collision of India into Asia 50 million years ago
caused the Eurasian Plate to crumple up and
override the Indian Plate. After the collision, the
slow continuous convergence of the two plates
over millions of years pushed up the Himalayas
and the Tibetan Plateau to their present heights.
Most of this growth occurred during the past 10
million years.
• And, transform boundaries where plates
slide past each other, ideally with little or
no vertical movement. Most transform
boundaries are below sea level and so not
easy to see. The San Andreas fault in
California is a transform boundary.
Transform-Fault Boundaries
• Transform-Fault Boundaries are where two
plates are sliding horizontally past one
another. These are also known as transform
boundaries or more commonly as faults.
• Most transform faults are found on the ocean floor
and are generally defined by shallow earthquakes.
A few, however, occur on land. The San Andreas
fault zone in California is a transform fault. The
San Andreas is one of the few transform faults
exposed on land. The San Andreas fault zone,
which is about 1,300 km long and in places tens of
kilometers wide, slices through two thirds of the
length of California. Along it, the Pacific Plate has
been grinding horizontally past the North
American Plate for 10 million years, at an average
rate of about 5 cm/yr. Land on the west side of the
fault zone (on the Pacific Plate) is moving in a
northwesterly direction relative to the land on the
east side of the fault zone (on the North American
Plate).
ocean-to-continent convergence
ocean-to-ocean convergence
continent-to-continent convergence
Examples: subduction zones which occur at deep sea trenches such as the Marianas
Trench, and sites of continental collision forming mountain belts, such as the
Himalaya Mountains, the Ural Mountains, the Appalachian Mountains, and the Alps.
Animation of convergent plate motion
Transform - where the plates are sliding past one
another, such as one sliding to the north and the adjacent
plate sliding to the south.
Examples: transform faults (easily seen where they cut
at right angles to the mid-ocean ridges); includes the San
Andreas fault.
Geologic Processes that occur at
plate boundaries
PLATE TECTONICS AND THE
EARTH'S EVOLUTION
• When the earth originated it contained no continents
• There were only a few kinds of igneous rock – rock
made from cooled lava.
• Then, due to plate movement…volcanoes formed
island chains
• and then these enlarged to form the large continental
masses we live on today.
• at convergent and divergent plate boundaries, new
rock is formed due to the magma.
• This magma cooled and fractured eventually creating
the continental masses.
Supercontinents
•
•
•
•
•
Continents grew
Came together
Drifted apart
Came together again
They fragment and form smaller isolated
continents
Pangaea
• The last supercontinent
• formed about 300 million years ago when the
isolated continents collided.
• During its existence only the one large continent
existed, balanced by one large ocean, Panthalassa.
During the fragmentation stage (beginning about
230 million years ago and still going on) the
present Atlantic ocean opened up, and all the
continents are now scattering across the globe.
Watch pangaea video on disk
• The present day Atlantic ocean is getting
wider because of sea floor spreading.
• But since the earth is spherical that means
things must be coming together some place
else, and that is in the Pacific ocean.
• The Pacific ocean is getting smaller along
subduction zones (convergent plate
boundaries) under North and South
America, and Japan, as western North
America and Asia get closer together.
• Sometime in the future the Pacific ocean
will close completely and Asia and North
America will collide to form another
supercontinent.
• The history of Gondwana and Rodinia tell
us that this supercontinent will not stay
together long either, and will fragment into
isolated continents scattered across the earth
again.
• The main force that shapes our planet’s
surface over long amounts of time is the
movement of Earth's outer layer by the
process of plate tectonics.
• Movements deep within the Earth, which
carry heat from the hot interior to the cooler
surface, cause the plates to move very
slowly on the surface, about 2 inches per
year.
• Interesting things happen at the edges of
plates. Subduction zones form when plates
crash into each other, spreading ridges form
when plates pull away from each other, and
large faults form when plates slide past each
other.
Rock Evidence for Continental
Drift
• There are lots of rocks in Antarctica, but the
one that scientists just found is special. It
may provide evidence that part of
Antarctica was connected to North America
hundreds of millions of years ago.
• The rock, made of granite - a common
intrusive igneous rock, was found on a
glacier in Antarctica by a team of scientists
who are trying to figure out how the
continents were connected into a large
supercontinent named Rodinia hundreds of
millions of years ago.
• This rock supports the hypothesis that about
600-800 million years ago part of the
supercontinent broke away from what is
now the southwestern United States and
drifted south to become eastern Antarctica
and Australia.
• The rock was taken to laboratories for testing to
see if its chemistry was like that of rocks in the
US. They found that the rock is very similar to
igneous rocks in the United States. Particularly, it
is similar to rocks that are found in parts of
California, New Mexico, Kansas, and Illinois, as
well as New Brunswick and Newfoundland in
Canada. The rocks in this area were part of the
supercontinent Rodinia.
• Figuring out where continents where hundreds of
millions of years ago is a bit like putting a jigsaw
puzzle together. The pieces are the continents we
have today, but they have been moved from where
they used to be because of plate tectonics. By
finding rocks on different continents that are made
of the same minerals and chemicals, scientists can
piece together where the continents used to be
located and how they were connected.
Why is the Earth so restless?
What causes the ground to shake
violently, volcanoes to erupt with
explosive force, and great
mountain ranges to rise to
impressive heights?
• The answers to these questions were
discovered as one of sciences’ most
revolutionary and recent theories took
shape. It began with Alfred Wegener…
Continental Drift
• Alfred Wegener (German Astronomer and
Meteorologist) proposed in 1914 that all
landmasses were at one time connected as a
supercontinent approximately 200 million years
ago which he called Pangaea. In Wegener’s theory
of continental drift, Pangaea progressively split up
as the continents detached themselves and
“drifted” away. Wegener provided physical, fossil,
geological, and climate evidence to support this
theory;
• Fit of the continents
• Wegener noted that the shape of the
continent’s coastlines appeared to match
like pieces in a jigsaw puzzle.
• Fossil evidence (Mesosaurus,
Lystrosaurus, Glossopteris)
• Noted the occurrence of plant and animal fossils
found on the match coastlines of South America
and Africa. (Figure 1)
the locations of certain fossil plants and animals on present-day, widely
separated continents would form definite patterns (shown by the bands of
colors), if the continents are rejoined. (from
http://earthobservatory.nasa.gov/Library/Giants/Wegener/wegener_4.htm
l)
• Rock type and structural correlations
• • Similar age, structure, and rock types on
continents on opposite sides of the Atlantic
Ocean. i.e. Appalachian Mountains (North
America) and mountains in Scotland and
Scandinavia
• • Paleoclimatic evidence
• • Found dramatic climate changes on some
continents. Most notable was the discovery
of coal deposits (made of tropical plants) in
Antarctica which led Wegener to conclude
that this frozen continent in an earlier time
in Earth’s history must have been positioned
closer to the equator – where the milder
climate allowed lush, swampy vegetation to
grow. (Figure 2)
Figure 2: Paleoclimatic evidence for continental drift.
(from http://www.geology.ohiostate.edu/~vonfrese/gs100/lect25/index.html)
• Detailed information regarding Wegener’s
evidence can be found at;
http://pubs.usgs.gov/gip/dynamic/historical.
html
http://www.geology.ohiostate.edu/~vonfrese/gs100/lect25/
• The main reason Wegener’s hypothesis was not
accepted was because he suggested no mechanism
for moving the continents. His belief that the force
of Earth’s spin (rotation) was enough to cause the
continents to move was not shared by the
geologists of the time who knew that rocks were
too strong for this to be true.
• For an article outlining the grand vision of drifting
continents and widening seas to explain the
evolution of Earth’s geography and his theory of
continental drift, go to
http://earthobservatory.nasa.gov/Library/Giants/W
egener/
History of Plate Tetonics
• The idea that continents can move was
proposed by Wegener in 1915 on the basis
of fossil evidence, the way in which
coastlines seemed to fit together, and other
features, but it was not widely accepted at
the time.
• Evidence that led to the development of
plate tectonic theory in the 1960s came
primarily from new data from the sea floor,
including topography and the magnetism of
rocks.
• Seafloor spreading was proposed as a
mechanism to drive the movement of the
continents on the basis of symmetrical
patterns of reversed and normal magnetic
rocks on the sea floor.
• The Himalayas are often referred to as the "roof of
the world" because they host the highest peaks on
earth, most famously Mt. Everest at 8,848 meters
above sea level. The rock that caps Mt. Everest is
limestone, which forms at the bottom of warm,
shallow seas and is composed entirely of
fossilized marine creatures, everything from
plankton to clams and fish. For years, geologists
struggled to explain how the hardened remains of
tiny sea organisms could exist at the top of a
mountain range.
Permian
Jurassic
225 million years
135 million years
ago
ago
Today
• Geologic events are Earth changes that
occur rapidly such as faults, earthquakes
and volcanoes
Watch video nasa plate tetonics
and fossil
• Volcano short movie on disk
This Dynamic Earth: The Story
of Plate Tectonics
by W. Jacquelyn Kious and Robert I. Tilling.
An outstanding resource covering the
historical perspective, development the
theory, understanding plate motion, and
plate tectonics and people. It is available as
an online edition and as a downloadable
PDF edition (77 pages, 3.7MB) at
http://pubs.usgs.gov/gip/dynamic/dynamic.h
tml
Plot that Quake!
• The goal of this exercise is to motivate
students to question why earthquakes and
volcanoes occur where they do. Students
plot earthquake data over time in order to
discover that a pattern develops in the
occurrence of earthquakes worldwide.
http://seismo.berkeley.edu/istat/ex_quake_p
lot/
Berkeley Seismological
Laboratory
• This site is a great starting place which contains a
worldwide earthquake catalog, along with links to
United States seismic data, and a map of
California and Nevada earthquakes.
http://seismo.berkeley.edu/faq/catalog_0.html
• Link to education and outreach activities,
http://seismo.berkeley.edu/iup.overview.html
Earth Science Education
• Professor Larry Braile of Purdue University
has complied links with a great deal of
activities, simulations, teaching modules,
and investigations targeting earthquakes and
plate tectonics.
http://web.ics.purdue.edu/~braile/educindex
/educindex.htm
• IRIS (Incorporated Research Institutions for
Seismology
The IRIS website contains a host of lesson
plans and resources for educators along
with earthquake maps, lists, and interactive
software. To access IRIS
Education and Outreach, go to
http://www.iris.washington.edu/about/ENO/
index.htm
• Southern California Integrated GPS Education
Module
For simulations showing animated divergent (midocean ridge) boundary, convection in the mantle
and seafloor spreading, and convergent
(subduction) boundary, go to
http://scign.jpl.nasa.gov/learn/plate4.htm
Associated activities,
http://scign.jpl.nasa.gov/learn/activity.htm
• Earthquakes/tectonics
This site is a great educational resource, which
provides students with numerous links for
studying continental drift, plate tectonics, the
structure of the Earth, earthquakes, and seismic
waves. The following is a link to animations,
simulations and additional teaching resources
within the science of geology.
http://www.scienceman.com/pgs/00_links_geolog
y.html
• http://www.coolschool.ca/content/showcase.
php?type=science
Sea Floor Spreading
• Harry Hess (geologist and Navy submarine
commander during WWII) studied newly published
maps of the seafloor topography indicating the
existence of a world-wide mid-ocean ridge system.
He proposed, in the 1960’s, that ridges are where
new seafloor is created from upwelling in the mantle.
It was possible, he stated, that molten magma from
beneath the earth’s crust could ooze up between
plates and as this hot magma cooled, it would expand
and push on either side of it. He also proposed
subduction as a mechanism for recycling of the
seafloor. His theory provided a mechanism for
continental movement that Wegener’s model was
lacking.
Volcanoes
•
•
•
Volcanoes can occur where two tectonic plates move against each other or over special
regions called ‘hot spots’.
Eruptions occur when magma rises from the mantle and bursts through the surface of the
Earth to become lava. A main pipe or vent connects the mantle to the crater at the
Earth’s surface and other side pipes can also form. How a volcano erupts and the shape
of a volcano depends on the magma. For example some magma forms thick lava which
flows slowly and doesn’t travel very far before it cools and sets, so it forms steep sided
volcanoes. Very thick lava can also ‘clog’ the vent so that pressure builds up and an
eruption can be explosive with rocks and clouds of ash being thrown out.
Hot spots are sources of high heat below the mantle that seem to ‘burn through’ the
Earth’s crust at a weak spot. These volcanoes mainly erupt lava with very little ash. This
type of volcano is often found on the bottom of the ocean where it continually releases
lava that is cooled by the sea. Eventually enough lava is built up to form a small island.
The entire chain of Hawaii’s islands was created as a tectonic plate moved slowly over a
hot spot.
Earthquakes
•
Tectonic plates that form the surface of the Earth slowly move around, but
sometimes the jagged edges of plates lock together. Stress builds until
something gives and a large amount of energy is suddenly released at a point
called the focus. The surface of the Earth immediately above the focus is
called the epicentre. The energy travels in all directions through the Earth as
seismic waves. Some seismic waves travel quickly and squeeze and stretch the
rocks, some waves make the rock move up and down. Other waves cause a
circular motion near the surface of the Earth and cause most damage.
• Samples of the
deep ocean
floor show that
basaltic oceanic
crust become
progressively
older as one
moves away
from the midocean ridge.
(Figure 3)
• • The rock making up the ocean floor is
considerably younger than the continents –
no rock samples older than 200 million
years are found in the ocean crust while
ages in excess of 3 billion years can be
found in continental rocks.
• Paleomagnetism studies of the ocean floor demonstrate that the
orientation of the Earth’s magnetic field has changed over time.
(Figure 4)
• Figure 4: A theoretical model of the formation of
magnetic striping. New oceanic crust forming
continuously at the crest of the mid-ocean ridge,
cools and becomes increasingly older as it moves
away from the ridge crest with the spreading of
the seafloor: a. the spreading ridge about 5 million
years ago; b. about 2 to 3 million years ago; and c.
present-day (from
http://pubs.usgs.gov/gip/dynamic/developing.html
).
For detailed background on ocean floor mapping,
magnetic striping and polar reversals, go to
http://pubs.usgs.gov/gip/dynamic/developing.html
Plate Tectonics
• Since the early 1960s, the emergence of the theory of plate tectonics started a
revolution in the Earth Sciences. The theory has revolutionized our
understanding of the dynamic planet upon which we live. Unifying the study of
Earth, the theory has drawn together the many branches of earth science, from
paleontology (the study of fossils) to seismology (the study of earthquakes) to
volcanism and mountain building. It provides explanations as to why
earthquakes and volcanic eruptions occur in very specific areas around the
world, and how and why great mountain ranges like the Alps and Himalayas
formed.
• The theory of plate tectonics states that the Earth’s rigid outermost layer
(lithosphere) is fragmented into seven major plates and over a dozen smaller
plates that are moving relative to one another as they ride atop the hotter, more
mobile material of the asthenosphere (Figure 5 and 6). The primary force
responsible for the movement of the plates is heat transfer which sets up
convection currents within the upper mantle.
Figure 5: The layer of Earth we live on is broken into a dozen or so
rigid plates
(from http://pubs.usgs.gov/gip/dynamic/slabs.html)
• The boundary between these lithospheric
plates is where most of the action
(earthquakes) takes place. Three primary
plate boundaries exist (Figure 6);
• • Divergent boundaries – where new crust is
created as the plates pull away from each
other (mid-ocean ridge)
• Convergent boundaries – where crust is
recycled back into the mantle
• Transform boundary – where plates slide
horizontally past one another
• Figure 6: Artist's cross section illustrating the main
types of plate boundaries (see text); East African
Rift Zone is a good example of a continental rift
zone. (Cross section by José F. Vigil from This
Dynamic Planet -- a wall map produced jointly by
the U.S. Geological Survey, the Smithsonian
Institution, and the U.S. Naval Research
Laboratory.) (from
http://pubs.usgs.gov/gip/dynamic/Vigil.html)
• For simulations showing animated divergent
(mid-ocean ridge) boundary, convection in
the mantle and seafloor spreading, and
convergent (subduction) boundary, go to
http://scign.jpl.nasa.gov/learn/plate4.htm
Earthquakes
• Hold a wooden pencil at its ends and push up with your
thumbs in the middle. The pencil will bend with little
stress placed upon it. However, apply too much stress
and the pencil snaps – rapidly releasing its stored
energy. The rocks of the lithosphere act in a similar
manner to the pencil. Due to relative plate motion,
rocks of the lithosphere are under considerable stress.
An earthquake is a phenomenon that results from the
sudden release of stored energy in the Earth’s crust that
generates seismic waves. The boundaries between
Earth’s plates are where earthquake (and volcano)
occurrences are concentrated (Figure 7).
Figure 7: World seismicity map revealing earthquake occurrences are
concentrated in zones around the world (from
http://earthquake.usgs.gov/regional/world/seismicity/index.php).
• Each and every earthquake generates
Primary (P-wave) and Secondary (S-wave)
seismic waves. P-waves are compression or
longitudinal waves that travel the fastest of
all seismic waves. P-waves travel through
solids, liquids, and gases. S-waves are shear
or transverse waves which travel slower and
pass through solids only.
Figure 8: The different types of motion in P and S waves
http://www.exploratorium.edu/faultline/basics/waves.html
• For more information the science of
earthquakes and characteristics and
behavior of seismic waves, go to
http://www.earthquake.gov/learning/kids/eq
science.php
Figure 9: Earth’s internal structure as inferred from the study of
seismic waves
http://www.seed.slb.com/en/scictr/watch/living_planet/beneath.htm
• To learn more about seismic waves and Earth’s
interior, go to
http://www.solarviews.com/eng/earthint.htm
•
USGS facts about earthquakes can be found at,
http://earthquake.usgs.gov/learning/kids/facts.php
Common misconceptions associated with
this benchmark:
• 1. Students incorrectly believe that the continents randomly drift about the
Earth or that the continents are no longer moving.
• Continental Drift, the supercontinent Pangaea, and plate tectonics are likely
terms with which students are familiar, however the idea that continents are
still on the move today offers a challenge to students and adults.
Considering the two timescales involved - human timescale (say 10,000
years of civilization) of observation is far too limited compared to the
processes of plate tectonic occurring on a geologic timescale (tens and
hundreds of millions of years).
• For more on this and other misconceptions related continental drift visit
http://departments.weber.edu/sciencecenter/earth%20science%20misconcep
tions.htm
http://k12s.phast.umass.edu/~nasa/misconceptions.html
• For more on slow but continuous change, go to
http://www.project2061.org/publications/textbook/mgsci/report/Glencoe/GL
EN_es2.htm
Common misconceptions associated with
this benchmark:
• 2. Students incorrectly believe that California will split apart from the rest of
the United States and become an island (or fall into the Pacific Ocean),
leaving parts of Southern Nevada with oceanfront property.
• The San Andreas Fault is a transform plate boundary that exists between the
North American Plate and the Pacific Plate. This means that the land west of
the San Andreas Fault is sliding northwest past the rest of the United States,
towards San Francisco. This sliding does not create any space between the
two plates for water to fill in, in fact the two plates are actually being
pushed together by the two plate’s relative motions as they slide horizontally
by each other (VERY slowly).
• For more on this and other misconceptions related to earthquakes go to
Earthquake Country Southern California’s website, separating fact from
fiction, at
http://www.earthquakecountry.info/10.5/MajorMovieMisconceptions/
Assessment
• 1st Item Specification: Describe how
convection in Earth’s mantle has changed
the locations and shapes of continents based
on tectonic plate movement.
Depth of Knowledge Level 1
Use the diagrams below to answer the question.
Which diagram correctly shows how mantle convection currents
are most likely moving beneath colliding lithospheric plates?
A. Diagram 1
B. Diagram 2
C. Diagram 3
D. Diagram 4
Which part of Earth’s interior is inferred
to have convection currents that
cause tectonic plates to move?
A. Rigid mantle
• Asthenosphere
• Outer core
• Inner core
The movement of tectonic plates is
inferred by many scientists to be driven by
A. tidal motions in the hydrosphere.
B. density differences in the troposphere.
• convection currents in the
asthenosphere.
• olidification in the lithosphere.
The cross section below shows the direction of
movement of an oceanic plate over a mantle hot
spot, resulting in the formation of a chain of
volcanoes labeled A, B, C, and D. The geologic
age of volcano C is shown.
What are the most likely geologic ages of volcanoes
B and D?
A. B is 5 million years old and D is 12 million years old.
B. B is 2 million years old and D is 6 million years old.
C. B is 9 million years old and D is 9 million years old.
D. B is 10 million years old and D is 4 million years old.
The cross section below shows the direction of movement of an oceanic
plate over a mantle hot spot, resulting in the formation of a chain of
volcanoes labeled A, B, C, and D. The geologic age of volcano C is
shown.
The geographic position of Australia on Earth’s surface has been
changing mainly because
A. the gravitational force of the Moon has been pulling on Earth’s
landmasses forcing them to move.
B. the tilt of Earth’s axis has changed several times shifting Earth’s
landmass
C. Earth’s rotation has spun Australia into different locations.
D. temperature differences have been creating convection currents
in Earth’s interior moving landmasses.
2nd Item Specification: Identify
the evidence for seafloor
spreading.
• http://www.rpdp.net/sciencetips_v2/E12C2.
htm
3rd Item Specification: Identify
the three major types of tectonic
plate boundaries.
Diagram 1
Diagram 2
Diagram 3
Diagram 4
Which cross section best represents the crustal
plate motion that is the primary cause of the
volcanoes and deep rift valleys found at the
mid-ocean ridges?
A. Diagram 1
B. Diagram 2
C. Diagram 3
D. Diagram 4
Which type of plate boundary is shown in the diagram?
A. Divergent
B. Transform
C. Convergent
D. Universal
Which type of plate boundary occurs along the San Andreas Fault?
A.Transform
B.Universal
C.Convergent
D.Divergent
Base your answers to the question on the map, which shows the
location of mid-ocean ridges and the age of some oceanic bedrock
near these ridges. Letters A through D are locations on the surface
of the ocean floor.
Oceanic bedrock on either side of a mid-ocean ridge is supporting
evidence that at the ridges, tectonic plates are
A. diverging.
B. converging
C. locked into place
D. being subducted
Common misconceptions associated with
this benchmark:
• 3. Students incorrectly believe that Earth’s crust is several
100’s of kilometers thick.
• Earth’s crust consists of two types; continental and oceanic.
The less dense continental crust is the thickest, having an
average thickness of approximately 30 km while the much
thinner and more dense oceanic crust has an average thickness
of approximately 5 km. In fact, Earth’s crust occupies less than
1% of Earth’s total volume and represents the extent to which
the deepest wells drilled have not exceeded.
• http://www.nagt.org/files/nagt/jge/abstracts/Steer_v53p415.pdf
• For details about Earth’s Interior go to,
http://pubs.usgs.gov/gip/dynamic/inside.html