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Earth Science

Content Benchmark E.8.C.3
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 Earth Science Atmospheric Process and Water Cycle Solar System and Universe Earths Composition and Structure E.8.C.1 E.8.C.2 E.8.C.3 E.8.C.4 E.8.C.5 E.8.C.6 E.8.C.7 E.8.C.8 Content Areas Nature of Science (NOS) Life Science Earth Science Physical Science

Students know Earth is composed of a crust (both continental and oceanic); hot convecting mantle; and dense, a metallic core. E/S

Anyone who has attended elementary school knows Earth is layered. Most can even identify the layers as; inner core, outer core, mantle, and crust. But rarely can one answer the following questions:

What is each layer of the earth made of?
What is going on in each layer of the Earth?
How do we know about all the layers of Earth?

Although the interior of Earth is only ~40km beneath our feet, it is more difficult to reach than the moon! Twelve kilometers is as deep as anyone has ever dug underneath Earth’s surface. So, how do we know that Earth has four layers and each layer is made of different materials? It is these questions that scientists try to find answers to using both direct and indirect science processes. Current information comes from studying earthquake waves travelling through the Earth, as well as from laboratory experiments on surface minerals and rocks at high pressure and temperature.

Earth’s Structure

Earth is composed of three basic layers; core, mantle, and crust. The core represents 15% of Earth’s volume, the mantle 84%, and the crust only 1%. Each of the layers is unique in what materials compose it, specifically in regards to density, temperature, and unique properties. Let’s use diagrams to give a detail description of each layer of Earth.

The Crust

Figure 2. This diagram shows the crust in relation to other layers and depicts the
differences between continental and oceanic crust.
(From http://www.vulkaner.no/v/vulkinfo/tomtech/etomtech.html)

Sometimes compared to the skin of an apple or peach, Earths’ crust is the thinnest layer. It is composed of two types of crustal material; continental and oceanic. Landmasses are composed predominately of continental crustal material, while oceanic crust is the material that typically makes up the floor of ocean basins. The main difference between the two crusts is density. Oceanic crust is composed of thin, but dense layers of Basaltic material. Its average density is 3.0 g/cm3. Continental crust is composed of thick, but less dense rock, mainly Granite. Its average density is 2.7g/cm3. Teaching density fits well in conjunction with this benchmark.

The following resources contain information about demonstrating or calculating density:

You Are My Density, an activity that compares the differences in crust densities,
http://www.usoe.k12.ut.us/curr/science/
sciber00/7th/earth/sciber/earthden.htm

Activities that are divided into two lists, grocery store “only” items, and “chemicals needed”,
http://www.elmhurst.edu/~chm/demos/index.html

Simple online activity that challenges students to calculate the density of different “types” of blocks, can be found at http://www.edinformatics.com/math_science/density.htm

The Mantle

Figure 3. The mantle and convection currents
(From http://www.windows.ucar.edu/earth/images/convection.gif)

The Mantle is the thickest layer of the Earth and the most diverse. It has a large temperature range, the molten material behaves differently through out, and it is responsible for the movement of both continental and oceanic crust via convection currents.  Because the mantle is so thick, it has a large temperature difference between where it meets with the core and crust. At its deepest parts, near the core, the temperature can reach 4000 degrees Celsius, while directly under the crust, in the asthenosphere, the temperature is 500-900 degrees Celsius. Although these temperatures are well beyond melting points of rock material, the mantle consists of semi-solid molten rock material. The discrepancy in temperature causes the molten material to flow in a circular pattern, called a convection cell. Convection is defined as heat transfer by the upward movement of heated material and the downward movement of cooled material. It is caused by differences in temperature and density.

Convection Currents

Figure 4 & 5. Convection examples
(From http://www.acer-acre.org/ClimateChangeCD/sec3/311a.htm)

For a colorful visual of how convection currents move the crustal plates and can produce both rifting and mountain building, visit
http://education.sdsc.edu/optiputer/flash/convection.htm

For a colorful visual of convection currents in the mantel, visit
http://homepages.see.leeds.ac.uk/~eargah/Conv.html

Convection currents are the driving force of plate tectonics. Plate tectonics is the movement of continental and oceanic crust. Earth’s crust is made up of many different plates that move towards, away, and along side one another.

Earth Floor is a site that discusses plate tectonics in student friendly terms,
http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html

The US Geological Services (USGS) site has links to plate tectonics and much more,
http://pubs.usgs.gov/gip/dynamic/dynamic.html

For animations explaining plate tectonics, go to
http://www.ucmp.berkeley.edu/geology/tectonics.html

The Core

Figure 7. The liquid and solid core
(From http://news.nationalgeographic.com/news
/2005/08/images/050824_earthcore.jpg
)

The core is often explained as two separate entities. The entire core is composed of iron and nickel, but the inner core is solid while the outer core is liquid. The inner core is solid due to the great pressure present at that depth beneath Earth’s surface. The origin of the Earth's magnetic field is not completely understood, but is thought to be associated with convection in the outer core causing the inner core to spin creating Earth’s magnetic field. The magnetic field blocks solar wind (ionized particles from the sun) from reaching the surface of the Earth and is one of the contributing factor in producing the Auroras (the northern and southern lights that can occur in the night sky at extreme latitudes).

Figure 8. Earth’s magnetic field
(From http://www1.fccj.edu/pacrews/new_page_35.htm)

For more detailed information of Earth’s magnetic field, see
Student friendly descriptions of the Earth’s Magnetic field and the Van Allen Belts,
http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html

British Geological Services site that discusses the Magnetic field and the flips and reversals it can experience, at
http://www.geomag.bgs.ac.uk/reversals.html

For illustrations and information about the Auroras, go to
http://csep10.phys.utk.edu/astr161/lect/earth/aurora.html

Content Benchmark E.8.C.3

Students know Earth is composed of a crust (both continental and oceanic); hot convecting mantle; and dense, a metallic core. E/S

Common misconceptions associated with this benchmark

1. Students incorrectly assume that what is known about the layers of Earth was gathered from “digging” down to the core.

Understanding Earth’s depth is very difficult for students. To confront this misconception, students need to learn how scientists have gathered their data about the layers of Earth and have an understanding of pressure and it effects on the melting point of materials. Additionally, knowledge of seismic wave travel through different earth materials should be explored.

For information on seismic waves and their relationship to Earth’s interior, go to
http://eqseis.geosc.psu.edu/~cammon/HTML/
Classes/IntroQuakes/Notes/waves_and_interior.html

2. Students have difficulty visualizing how semi-solid rock in the mantle flows.

Doing simple demonstrations of viscosity can help students understand how the mantle is able to flow and create convection currents. The following sites are provided;

For a very brief activity on viscosity using Honey, visit
http://www.princeton.edu/~gasdyn/Research/
T-C_Research_Folder/Viscosity_def.html

For a much more technical explanation of viscosity, visit
http://www.spacegrant.hawaii.edu/class_acts/ViscosityTe.html

For a simple explanation of how to build a viscosometer, visit
http://www.science-projects.com/Viscosity.htm

For an online application that lets student explore differences in viscosity, visit
http://www.seed.slb.com/en/scictr/lab/visco_exp/index.htm

3.
Students mistakenly believe that Earth’s continents are floating on ocean water.

Looking at images showing convection currents in water and using them to explain continental drift can fuel this misconception. When discussing oceanic and continental crust, it is essential to show students that the crust includes both land and the ocean floor. Water is not the division of continental crust.

To view maps showing all tectonic plates go to
http://pubs.usgs.gov/gip/dynamic/slabs.html

Content Benchmark E.8.C.3

Students know Earth is composed of a crust (both continental and oceanic); hot convecting mantle; and dense, a metallic core. E/S

Sample Test Questions

1st Item Specification: Given a model, identify the major structural elements of the Earth (i.e. continental and oceanic crusts, mantle, core).

Depth of Knowledge Level 1

1. Use the model of Earth below to answer the following question.
1. What is the number of the layer representing the mantle of Earth?
1. 1
2. 2
3. 3
4. 7
1. The primary cause of crustal movement is
1. conduction.
2. convection.
3. magnetism.
1. A major difference between continental crust and oceanic crust is
1. density.
2. gravity.
3. pressure.
4. temperature.
1. Which of the following is MOST similar between the inner and outer core of Earth?
1. Composition
2. Pressure
3. Movement
4. Density

Depth of Knowledge Level 2

1. Use the map of Earth’s Major Plates to answer the following question.
1. What do the black lines on the map represent?
1. They represent continental borders.
2. They represent the boarders of countries.
3. They outline the major ocean basins.
4. They outline the crustal plate boundaries.
1. Use the following diagram of a tectonic plate boundary to answer the following question.
1. Analyzing the diagram above, what can you infer the about the type of plate boundary being shown here?
1. Divergent boundary
2. Convergent boundary
3. Transform boundary
4. Static boundary
1. Which of the following is possible evidence that the Earth’s core has both a solid and liquid portion?
1. The Earth has a strong magnetic field that periodically fluctuates.
2. The Moon is held in orbit around the Earth by the gravitational attraction.
3. The Earth’s oceans experience 2 high tides and 2 low tides a day.
4. The visible light from the Sun is deflected by the Van Allen Belts.
1. Use the diagram showing liquid in a container being heated to answer the question that follows.
1. In what way can this diagram serve as a model for what is occurring in the interior of the Earth?
1. The interior of the Earth is composed of water.
2. The interior of the Earth is also heated with fire.
3. Both have circular movement of fluids due to convection.
4. Both have circular movement of fluids due to conduction.
1. Use the diagram below showing a model of a cross section of the Earth to answer the question that follows.
1. Which characteristics of the Earth’s interior are most likely being represented by this model?
1. Compositional as there are more than three layers
2. Compositional as the Earth is shown in layers.
3. Physical as there are depths indicated.
4. Physical as the core is divided into two sections.

Constructed Response E.8.C.3

1. Use the diagram to answer the following questions. The diagram is a cross-section model of Earth with several layers labeled with numbers.

1. Label the names of layers 1, 2, 6, and 7 on the diagram.
2. Describe the differences between continental and oceanic crust.
3. Provide an explanation for the process occurring within the Earth that drives plate tectonics.

Content Benchmark E.8.C.3

Students know Earth is composed of a crust (both continental and oceanic); hot convecting mantle; and dense, a metallic core. E/S

1. B, DOK level 1
2. B, DOK level 1
3. A, DOK level 1
4. A, DOK level 1
5. D, DOK level 2
6. B, DOK level 2
7. A, DOK level 2
8. C, DOK level 2
9. D, DOK level 2

Constructed Response Answer and Score Rubric

 3 points Response addresses all parts of the question clearly and correctly. Part A is a list of, Crust, Mantle, Outer Core, and Inner Core. Part B will include; density and rock type (Granite for Continental, Basalt for Oceanic). Continental crust (primarily granite) is less dense than Oceanic crust (primarily basalt). Part C will include; The core is the source of heat (from radioactive decay) that drives the convection currents in the mantel.  Heated magma rises through the mantel, as it rises the magma cools as it nears the surface / crust.  The magma moves horizontally pushing the crustal plates then sinking back into the mantel. 2 points Response addresses all parts of the question and includes only minor errors. 1 point Response does not address all parts of the question. 0 points Response is totally incorrect or no response provided.

Content Benchmark E.8.C.3

Students know Earth is composed of a crust (both continental and oceanic); hot convecting mantle; and dense, a metallic core. 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. 3-D models of Earth from Explorations in Earth Science

This site offers several ways to build models of Earth. Procedures for construction of a 3-D model of the interior of the Earth, to help visualize the main layers or regions - inner core, outer core, mantle and crust.  This project enhances visualization and illustration of the relative volumes of Earth’s layers.  This activity also provides an opportunity for some practice in problem solving and math skills.

To access this activity, visit
http://web.ics.purdue.edu/~braile/edumod/threedearth/threedearth.htm

2. How Do We Know About Layers of Earth? by ClassZone Exploring Earth

This is a great series of animations showing the layers of Earth and how waves travel through each layer. This site can be used to clear up misconceptions about how scientists understand the composition of the layers or as an extension for teaching wave movement. The following link takes you to a page (Step 1) containing images of A View of Earth from Above. Below the image are questions for discussion. “Steps” at the bottom of the page link to additional topics directly related to this benchmark such as; 2) A View from Below, 3) Seeing with Seismology, 4) Modeling Internal Structure, 5) Locating Layers, 6) Another Model, 7) Changing the Thickness of a Layer, 8) Structure of Earth, 9) Seismic Tomography, 10) Beneath the Surface, and 11) Find Out More About Seismic Tomography.

To access these animations, visit
http://www.classzone.com/books/earth_science/
terc/content/investigations/es0402/es0402page01.cfm

3. Convection Currents

There are a variety of ways to create convection in the classroom. However, if using a flame or hot plates is a safety issue these sites offer visual representations, simulations, and movies of convection.

Educators Guide to Convection from Jet Propulsion Laboratory contains convection animations and videos and can be accessed at
http://www.solarviews.com/eng/edu/convect.htm

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.

To access this animation, visit
http://www.classzone.com/books/earth_science/terc/
content/visualizations/es0805/es0805page01.cfm