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Performance Benchmark E.12.C.2
Students understand the concept of plate tectonics including the evidence that supports it
(structural, geophysical and paleontological evidence). E/S
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)
Figure 1: As noted by Snider-Pellegrini and Wegener, 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.html)

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.ohio-state.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.ohio-state.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/Wegener/
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.
Evidence that the seafloor is ever changing include;

Samples of the deep ocean floor show that basaltic oceanic crust become progressively
older as one moves away from the mid-ocean ridge. (Figure 3)
Figure 3: Crustal Age of the
Ocean Floor.
(from
http://www.ngdc.noaa.gov/mgg/ima
ge/images/AtlanticAge.jpg)

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. Pwaves 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/eqscience.php
The Earth’s radius is approximately 4000 miles (6,400 kilometers) and divided into four major
layers; crust, mantle, outer core and inner core. Diagrams like the one below (Figure 9) have
been constructed from the study of seismic waves, not from direct observation. The deepest
wells drilled only penetrate Earth’s crust to a depth of approximately 10 miles. As seismic
waves from an earthquake spread from the source (focus) outward, P and S-waves arrive at
seismic stations around the world at different times, yielding an “X-ray” image of Earth’s
internal structure.
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
Performance Benchmark E.12.C.2
Students understand the concept of plate tectonics including the evidence that supports it
(structural, geophysical and paleontological evidence). E/S
Common misconceptions associate 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%20misconceptions.htm
http://k12s.phast.umass.edu/~nasa/misconceptions.html
For more on slow but continuous change, got to
http://www.project2061.org/publications/textbook/mgsci/report/Glencoe/GLEN_es2.htm
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/
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
Performance Benchmark E.12.C.2
Students understand the concept of plate tectonics including the evidence that supports it
(structural, geophysical and paleontological evidence). E/S
Sample Test Questions
1. What type(s) of evidence did Alfred Wegener use to support his theory of Continental
Drift?
a.
b.
c.
d.
Earth’s magnetic field reversals discovered from ocean floor samples.
Molten material in the lithosphere pushed the continents in various directions.
Rocks of similar age, type, and structure found on widely-separated continents.
Core samples from the mantle of the Earth.
2. Why was Alfred Wegener’s theory of Continental Drift rejected by the scientific
community in the 1920’s?
a.
b.
c.
d.
The earth was thought to be too young for such movements.
Lack of a mechanism for continents to plough through oceanic crust.
The discovery of underwater mountains made continental drift unlikely.
The continental crust would have sunk as it drifted into the oceans.
3. The diagram below is a portion of Earth’s interior
Figure reference: http://www.nysedregents.org/testing/scire/sciarch/psestestja02.pdf
The arrows shown in the asthenosphere represent the inferred slow circulation of the
plastic mantle believed to drive plate motion. This process is called
a.
b.
c.
d.
Convection
Conduction
Radiation
Insolation
4. The diagram below is a portion of Earth’s interior
Figure reference: http://www.nysedregents.org/testing/scire/sciarch/psestestja02.pdf
Which layer contains the deepest wells humans have drilled to directly observe Earth’s
internal structure?
a.
b.
c.
d.
Crust
Mantle
Outer Core
Inner Core
5. The diagram below is a cross-section view of Earth which shows seismic waves traveling
from the focus of an earthquake. Points A and B are located on Earth’s surface. (Figure
reference: http://www.nysedregents.org/testing/scire/es106.pdf)
Which statement best explains why only one type of seismic wave was received at
location B?
a.
b.
c.
d.
S-waves cannot travel through the liquid outer core
S-waves cannot travel through the liquid inner core
P-waves cannot travel through the solid outer core
P-waves cannot travel through the solid inner core
6. Compared to the speed of S-waves in a given Earth material, the speed of P-waves is
a.
b.
c.
d.
always slower
always faster
always identical
sometimes slower and sometimes faster
7. A seismic station received the P-waves generated by an earthquake but did not receive
any S-waves. Which statement best explains the absence of S-waves?
a. The earthquake had a relatively small magnitude and therefore did not produce
any S-waves..
b. The earthquakes epicenter and focus were at the same location.
c. The S-waves were absorbed by a fluid layer as they traveled toward the seismic
station.
d. All of these are possible reasons.
8. Scientists have classified Earth’s internal structure into four zones based primarily on
evidence gained by studying
a.
b.
c.
d.
Earthquake seismic waves
Gravity measurements
Deep drill cores
Volcanic eruptions
9. Which information indicates that new seafloor rock is forming along the mid-ocean ridge
and then moving horizontally away from the ridge?
a. Most volcanoes are located under ocean water.
b. Paleomagnetic studies of the ocean floor demonstrate that the orientation of
Earth’s magnetic field has remained constant
c. Fossils of marine organisms can be found at high elevations on continents.
d. The age of the seafloor rock increases as the distance from the mid-ocean ridge
increases.
10. What does the plate tectonic theory predict about the distribution of volcanoes and
earthquakes?
a.
b.
c.
d.
They should occur primarily on continents.
They should be evenly distributed throughout the earth.
They should only occur along continental margins.
They should occur primarily along plate boundaries.
Performance Benchmark E.12.C.2
Students understand the concept of plate tectonics including the evidence that supports it
(structural, geophysical and paleontological evidence). E/S
Answers to Sample Test Questions
1. (c)
2. (b)
3. (a)
4. (a)
5. (a)
6. (b)
7. (c)
8. (a)
9. (d)
10. (d)
Performance Benchmark E.12.C.2
Students understand the concept of plate tectonics including the evidence that supports it
(structural, geophysical and paleontological evidence). E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. 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.html
2. Plot that Quake!
The goal of this exercise is to motivate students to question why earthquakes 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_plot/
3. 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
4. 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
5. 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
6. Southern California Integrated GPS Education Module
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
Associated activities,
http://scign.jpl.nasa.gov/learn/activity.htm
7. 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_geology.html