Content Benchmark E.8.C.4
Students know the very slow movement of large crustal plates result in geological events. E/S
The first journal question posed to students in an Introductory Geology class might be “If
weathering and erosion have been wearing away Earth’s surface for billions of years then why is
Earth’s surface not flat?” This question generates more reflection prior to being able to formulate
a response – i.e. rocks are really hard material, maybe some types cannot be broken down, and
more time would be needed to make it flat; possibly many more millions or billions of years.
Although the answer to this question seems more straightforward today, it is at the heart of this
benchmark.
Earth’s Internal Structure
The Earth is composed of primarily three basic layers; crust, mantle, and core. Understanding the
very slow movement of large crustal plates requires a brief review of the properties of these
layers. Earth’s crust is the thin, rigid outermost layer which varies in thickness from 5
Kilometers under the oceans (oceanic crust) to 70 Kilometers thick under portions of the
continents (continental crust). Below the rigid crust is the mantle. This complex layer contains
most of the Earth’s mass and is composed of primarily iron, magnesium, aluminum, and silicate
compounds which are solid but can deform slowly in a plastic-like manner. The high temperature
of the core radiates thermal energy to the upper layers. This heat transfer to the upper layers is
believed to provide the mechanism for plate movement, i.e. plate tectonics.
Figure 1. Cutaway view showing the internal structure of the Earth. This view drawn to scale
demonstrates that the Earth’s crust literally is only skin deep. Right: a view not drawn
to scale to show Earth’s three main layers (crust, mantle, and core) in more detail.
(From http://pubs.usgs.gov/gip/dynamic/inside.html)
For detailed information on the Structure of Earth’s Interior visit MS TIPS Benchmark E.8.C.3.
Earth’s Lithosphere is composed of crust (both oceanic and continental) and the stiffer part of the
upper mantle. The lithosphere is broken into several large and small plates (Figure 2). These
plates move about on the sturdy liquid portion of the upper mantle called the asthenosphere. The
rigid lithospheric plates float on the asthenosphere, although more complicated; much the same
way ice floats on water.
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. Figure 3 provides a visual of the
inferred convection currents set up in the mantle - areas of intense heat rise, cool, and eventually
sink back down in a continuous cycle.
Figure 3. Convection currents – large convection systems in the mantle may carry along plates of
the lithosphere like a conveyor belt. Image by: Colin Salmon, Dorling Kindersley
(From http://mediatheek.thinkquest.nl/~ll125/en/fullconvect.htm)
For more information on the mechanism for Plate Tectonics visit,
http://www.ucmp.berkeley.edu/geology/tecmech.html
and, http://www.windows.ucar.edu/tour/link=/earth/interior/how_plates_move.html&edu=high
For an advanced discussion of Plate Tectonics visit HS TIPS Benchmark E.12.C.2.
Geologic Events Resulting From Plate Movement
Understanding that Earth’s crust is broken into several large and many smaller plates and
convection currents are providing a force on these plates to move them, several effects can result.
Geologic events are Earth changes that occur rapidly such as faults, earthquakes and volcanoes
or changes that take considerably longer time such as mountain building, polar shifts, and global
warming. A brief overview of faults, earthquakes, volcanoes, and mountain building will be
presented, as they relate directly to “the slow movement of large crustal plates results in
geological events.”
Faults
A fault is a fracture in the Earth’s crust along which two blocks have slipped with respect to each
other. Faults are classified into three groups depending on how they move. Normal, reverse (or
thrust), and transform (or lateral) faults result from different directions of stress building from
plate movement. For example, a normal fault results from an extension stress “pulling” crust in
different directions, while reverse fault results from compression stress pushing crust together, as
shown in the figure below.
Figure 4. Three types of faults
(From http://wapi.isu.edu/Geo_Pgt/Mod03_PlanetaryEvo/images/Faults.GIF)
In addition to faults, folding of rock layers provide evidence of tectonic activity. When large
pieces of the Earth’s crust move laterally, they create huge compressional forces that can bend or
even break rocks. Here, the sedimentary rock layers show an anticlinal fold, in which the layers
bend downward from the crest.
Figure 5. Compressional force created folded rocks. V. Englebert/Photo Researchers, Inc.
(From http://encarta.msn.com/media_461530095/folded_rocks.html)
For additional information on the three fault types and images of real world examples of each,
visit National Oceanic and Atmospheric Administration/ National Geophysical Data Center
Images at
http://www.iris.washington.edu/gifs/slides/faults/slideshow/index.htm
Earthquakes
An earthquake is a sudden movement of the Earth, caused by the abrupt release of strain that has
accumulated over a long time. For hundreds of millions of years, the forces of plate tectonics
have shaped the Earth as the plates that form the Earth's surface slowly move over, under, and
past each other. Sometimes the movement is gradual. At other times, the plates are locked
together, unable to release the accumulating energy. When this energy elevates to the elastic
limit of the rocks, they will break. If the earthquake occurs in a populated area, it may cause
many deaths and injuries and extensive property damage.
Figure 6. Anatomy of an earthquake
(From http://t3.pacific.edu/teams/M031606/focus_epicenter.jpg)
For a 20 page online booklet that explains the nature and causes of earthquakes, describes
techniques used to detect, record, measure, and predict seismic disturbances go to
http://pubs.usgs.gov/gip/earthq1/
For a comprehensive review of earthquakes, along with a geology overview of earthquake wave
types and measurement visit PhysicalGeography.net at
http://www.physicalgeography.net/fundamentals/10m.html
For a two page Natural Hazards Fact Sheet on Earthquakes presented by the USGS, visit
http://pubs.usgs.gov/fs/2006/3016/2006-3016.pdf
Volcanoes
More than 80% of the Earth’s surface is volcanic in origin. The ocean floor is composed almost
entirely of basalt, an extrusive igneous rock. Countless eruptions of gas, ash, and lava have
created the seafloor and some of the mountains that make up Earth’s landscape. Volcanoes are
often referred to as windows into the upper mantle of Earth. Pressure within the mantle forces
magma to the surface through areas of weakness in the crust. The lava they erupt, in many times,
comes from 10’s of Kilometers below the surface. They are geological events that shape the
planet and often times their activity triggers earthquakes.
Figure 7. Anatomy of a volcano
(From http://www.tetonwyo.org/em/docs/images/volcano_diagram_usgs.gif)
For a comprehensive review of volcanoes, along with a geology overview of the three
classifications of volcanoes visit PhysicalGeography.net at
http://www.physicalgeography.net/fundamentals/10n.html
For a two page Natural Hazards Fact Sheet on Volcanoes presented by the USGS, visit
http://pubs.usgs.gov/fs/2006/3014/2006-3014.pdf
Volcanoes and Earthquakes are found in similar locations around the Earth, primarily controlled
by the location of lithospheric plate boundaries - zones of crustal weakness, and regions of
increased stress resulting from relative plate movement. The following two images illustrate this
relationship.
Figure 8. Earthquake occurrences plotted on World Map
(From http://www.geophysics.rice.edu/plateboundary/DPB_map_gifs/quakes.50percent.gif)
Figure 9. Volcanoes Plotted on World Map.
(From http://www.geophysics.rice.edu/plateboundary/volcano.72.gif)
For an article titled Plate Tectonics II: Plates, Plate Boundaries, and Driving Forces visit
http://www.visionlearning.com/library/module_viewer.php?mid=66
Mountain Building
Most mountains were created from tectonic forces that elevate, fold, and fault solid lithospheric
material. As the plates are slowly pushed and/or pulled, strain builds up in the rigid crust until
portions of the crust are uplifted or subducted. Mountains can be created from volcanic activity
and build to high elevations from the extrusion of immense amounts of lava. However, the
majority of mountains present across our planet resulted from tectonic activity.
For a comprehensive review of mountain building, along with a geology overview of the
evolution of mountains visit PhysicalGeography.net at
http://www.physicalgeography.net/fundamentals/10k.html
Figure 10 provides an excellent overview of the geologic events that result from the slow
movement of large crustal plates. In the middle section of the diagram oceanic plate (crust)
collides with continental plate (crust) – forming a subduction zone. The subducted oceanic plate
melts as it is pushed deeper into the mantle, providing a source of magma fueling the volcanic
mountain range on the surface. On the far right side of the image, a continent-continent plate
collision zone is shown. As these two plates are pushed together, a faulted and folded mountain
system is formed.
Figure 10. Plate motion and resulting geologic events
(http://www.jenningsk12.net/WE/peimann/Science/Earth%20Movements/subduction.jpg)
For a comprehensive description of plate motion and types of plate boundaries visit the United
States Geological Survey’s online publication This Dynamic Earth: the Story of Plate Tectonics
at http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288
Now to come back to the journal question posed in the introduction of this benchmark; If
weathering and erosion have been wearing away Earth’s surface for billions of years then why is
Earth’s surface not flat? As we have seen, there are both destructive and constructive forces
shaping the planet. Earthquakes, volcanoes, and mountain building are geologic events that result
from the very slow movement of large crustal plates. Although earthquake and volcanic events
may be “destructive” to society, they are responsible for creating much of the topography present
on our planet. While it is true that many natural forces are working to wear our planet away such
as weathering and erosion, there is the slow and continual movement of Earth’s crustal plates
from plate tectonics and eruption of volcanic material creating new landforms.
Content Benchmark E.8.C.4
Students know the very slow movement of large crustal plates result in geological events. E/S
Common misconceptions associated with this benchmark
1. Students may believe that continents do not move or that they randomly drift about the
Earth.
Considering the slow rate at which lithopsheric plates move – a rate of a few centimeters per
year (about the rate your fingernails grow), it is understandable that students would have
difficulty relating to this concept. To tell them that the formation of the Rocky Mountains
(Laramide Orogeny) began 70 to 80 million years ago and ended some 40 million years ago
or that Nevada has been geographically located south of the equator in the geologic past
would be challenging to accept for middle school science students as well as most adults
without a strong science background.
Figure 11. Changing locations of the continents over time
(From http://pubs.usgs.gov/gip/dynamic/historical.html)
For additional information related to this misconception and background to address it visit
http://www.cst.cmich.edu/users/Franc1m/esc105/lectures/plate.htm
and, http://departments.weber.edu/sciencecenter/earth%20science%20misconceptions.htm
2. Students may believe that tectonic plates move around on top of a sea of molten lava.
This misunderstanding is not applicable to only middle school science students, many adults
believe that below Earth’s crust lies a sea of molten magma, ready to break through and erupt
at any instant. While it is a fact that temperature increases with depth below Earth’s surface
(shown by the red line in the figure), what is often times overlooked (or misunderstood) is
that pressures also increase with depth. As pressure increases, so too does the melting point
of the material keeping the material in the solid state at these higher temperatures.
Figure 12. Temperature and pressure relationship to depth
(http://scienceblogs.com/highlyallochthonous/2008/01/annoying_misconceptions_in_geo.php)
For more information on this and other geology misconceptions visit
http://scienceblogs.com/highlyallochthonous/2008/01/annoying_misconceptions_in_geo.php
3. Students have many misconceptions related to earthquakes.
The Southern California Earthquake Center has prepared a comprehensive resource
separating fact from fiction, and dispelling common earthquake myths. A few examples of
each are provided here.
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Fiction: There can be a magnitude 10.5 earthquake
Fiction: California will split apart from the rest of the US and become an
island/oceanfront property in Barstow
Fiction: The earth will open and swallow a train, my car, my town, or me
Fiction: You can prevent large earthquakes by making lots of small ones, or by
“lubricating” the fault with water
To access the complete list of fiction beliefs and the facts behind them visit
http://www.earthquakecountry.info/10.5/MajorMovieMisconceptions.html
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Myth: Big earthquakes always happen in the morning
Myth: Beachfront property in Arizona
Myth: We have good building codes so we must have good buildings
Myth: We can cause earthquakes, nuclear explosions can start earthquakes
To access the complete list of earthquake myths and the correct explanations visit
http://www.earthquakecountry.info/10.5/myths.html
Content Benchmark E.8.C.4
Students know the very slow movement of large crustal plates result in geological events. E/S
Sample Test Questions
Questions and Answers to be inserted from separate file
Content Benchmark E.8.C.4
Students know the very slow movement of large crustal plates result in geological events. E/S
Answers to Sample Test Questions
Questions and Answers to be inserted from separate file
Content Benchmark E.8.C.4
Students know the very slow movement of large crustal plates result in geological events. 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. Convection Resources
Plate Tectonics II: Plates, Plate Boundaries, and Driving Forces from Visionlearning
This article provides a good overview of the types of plate boundaries, their interactions, and
the driving force behind plate movement; convection. This article can be accesses at
http://www.visionlearning.com/library/module_viewer.php?mid=66
Activity: Colorful Convection Currents from Steve Spangler Science
Simple materials and equipment for demonstrating convection currents can be accessed at
http://www.stevespanglerscience.com/experiment/00000031
Visualization: Observe an animation of convection in the mantle from McDougal Littell
This animation shows a cross section of Earth; it illustrates a mathematical model of how
convection might occur in the mantle. Diagrams of convection cells in the mantle are often
highly simplified, but researchers are finding that the real world is much more complex.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0805/es0805pag
e01.cfm
2. Plate Tectonics Resources
Plate Tectonics Lesson from Teachers Domain
This site requires user to register, but registration is free. This two-day lesson’s three
objectives are; 1. Understand how Earth is dynamic and how moving plates form ocean
basins, mountain ranges, islands, volcanoes, and earthquakes, 2. Identify the three general
categories of plate boundaries recognized by scientists: convergent, divergent, and transform.
3. Understand how the theory of plate tectonics was developed and supported. Additionally,
several links to high-quality multimedia resources are provided at
http://www.teachersdomain.org/resource/ess05.sci.ess.earthsys.lp_platetectonics/
For a comprehensive description of plate motion and types of plate boundaries visit the
United States Geological Survey’s online publication This Dynamic Earth: the Story of Plate
Tectonics at
http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288
3. Earthquake Resources
Incorporated Research Institutions for Seismology (IRIS)
A GREAT resource for teaching about earthquakes! The following link will take you to the
Education and Outreach portion of their website which has a myriad of resources such as;
Demonstrations, Posters, Activities, Animations, Presentations, and Videos all classified by
audience level with a complete description of the intervention. Over 40 resources are
presented here!
http://www.iris.edu/hq/programs/education_and_outreach/resources
Earthquake by Kaye M. Shedlock & Louis C. Pakiser from the USGS
This 20 page online booklet explains the nature and causes of earthquakes, describes
techniques used to detect, record, measure, and predict seismic disturbances. Access this
resource at
http://pubs.usgs.gov/gip/earthq1/
Earthquakes Overview from Physical Geography
For a comprehensive review of earthquakes, along with a geologic overview of earthquake
wave types and measurement go to
http://www.physicalgeography.net/fundamentals/10m.html
4. Volcanoes Resources
United States Geological Society (USGS) Educational Resources Index
This link will take you to the USGS resources index on volcanoes for middle and high school
science topics. Activities, simulations, images, and teacher packets are found at
http://education.usgs.gov/common/secondary.htm#volcanoes
Volcanoes Overview from Physical Geography
For a comprehensive review of volcanoes, along with a geology overview of the three
classifications of volcanoes visit
http://www.physicalgeography.net/fundamentals/10n.html
Natural Hazards Fact Sheet on Volcanoes from the USGS
This is a 2 page pdf document that provides facts about volcanoes, the threat they pose to
society and links for further information. To download this sheet, go to
http://pubs.usgs.gov/fs/2006/3014/2006-3014.pdf