what lies beneath?
(2 Hours)
In this activity, students will build a model to show several layers of different rock types. They will then
use simple tools to sample the layers and create a cross-sectional map of the subsurface layers.
Overview
Topic: Earth’s layers
Real-World Science Topics:
• An exploration of the different layers that make up Earth’s crust
• An exploration of rock and soil types
• An exploration of creating maps for various purposes
Objective
Students will gain an understanding of the ways subsurface layers of Earth’s crust can vary, and
they will develop a method for mapping these subsurface layers. Materials Needed for Teacher Demonstration
• access to the outdoors
• prepared bin with layers of soil (see Teacher Preparation)
Materials Needed for Student Teams
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opaque plastic bin
clay
sand
potting soil
small pea gravel
toothpicks
rulers
clear plastic straws
two sheets of paper
Teacher Preparation
Prepare the plastic bin with soil layers ahead of time for each group of students. To do this, begin
with a layer of clay and/or wet sand. Clay or wet sand is the best material for the bottom layer, as
it helps “plug” the straw when students take core samples. Then, add other materials such as small
gravel and potting soil on top of the bottom layer. Vary the depth of each layer at different points
in the bin. Then, label the bin with a grid system. The photos on the next page show the layers
being constructed within the bin (with layers of varying thickness).
If you opt to have your students build the bin with layers, it will still be helpful to prepare a sample
model for students. To make sure your model is successful, use soft clay so the straw will be able
to penetrate through that layer. Also, wet sand works better than dry sand, as dry sand can slip
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what lies beneath?
(2 Hours)
out of the straw. Finally, make sure all of the layers are well compacted. When students take core
samples, their straws can compress the different layers. Well-compacted layers can help alleviate
this problem. The plastic bin used in the pictures is shown to illustrate the layers of soil that should
be constructed. However, the actual bins used for student investigations should be opaque so that
students cannot see the layers.
Standards Met
National Science Standards Addressed
CONTENT STANDARD A:
As a result of activities in grades 5-8, all students should develop
• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry
CONTENT STANDARD B:
As a result of activities in grades 5-8, all students should develop an understanding of
• Properties and changes of properties in matter
CONTENT STANDARD D:
As a result of activities in grades 5-8, all students should develop an understanding of
• Structure of the earth system
• Earth’s history
CONTENT STANDARD E:
As a result of activities in grades 5-8, all students should develop
• Abilities of technological design
• Understandings about science and technology
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what lies beneath?
(2 Hours)
CONTENT STANDARD F:
As a result of activities in grades 5-8, all students should develop an understanding of
• Natural hazards
• Risks and benefits
• Science and technology in society
National Math Standards Addressed
• Select appropriate methods and tools for computing with whole numbers from among mental
computation, estimation, calculators, and paper and pencil according to the context and nature
of the computation and use the selected method or tools
• Represent and analyze patterns and functions, using words, tables, and graphs
• Identify and describe situations with constant or varying rates of change and compare them
• Make and use coordinate systems to specify locations and to describe paths
• Identify and draw a two-dimensional representation of a three-dimensional object
National Technology Standards Addressed
Creativity and Innovation Students demonstrate creative thinking, construct knowledge, and develop innovative products
and processes using technology. Students:
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Apply existing knowledge to generate new ideas, products, or processes.
Create original works as a means of personal or group expression.
Use models and simulations to explore complex systems and issues.
Identify trends and forecast possibilities.
Sources
National Science Teachers Association, http://books.nap.edu/html/nses/overview.html
National Council of Teachers of Mathematics, http://standards.nctm.org/document
National Educational Technology Standards, http://cnets.iste.org/currstands/cstads-netss.html
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Steps for
what lies beneath?
1. Warm-up Activity: If possible, take your students outside for a few minutes. Ask them to make
observations about the ground, including details about the top layer of soil. Then, ask students
to guess what is below that top layer of soil. Student answers might include things like bedrock,
gravel, or water. Ask students to brainstorm ways that they could learn about the layers of Earth
that are beneath their feet. Explain that these are called subsurface layers. (It may help to explain
that the prefix “sub-” means “below,” so subsurface layers are layers that are below a surface.)
Use their answers to help you gauge their preexisting knowledge about the layers of Earth and
subsurface mapping. Then, tell students that in this activity, they will learn one technique that
scientists use to figure out what layers are beneath the surface of Earth.
2. B
ring the class inside and show them the pre-prepared bin that represents the subsurface layers
of Earth. Explain to students that there are several different layers, such as clay, sand, gravel, and
soil. Their job will be to determine the thicknesses of each layer at several points in the bin.
3. Divide students into groups of six. Distribute the prepared bins, toothpicks, rulers, paper, and clear
plastic straws along with the Student Handouts. Explain to students that they will create a grid
system so that they can map the layers of soil in an organized way. To do this, students will insert
12 toothpicks into the bin, at evenly spaced intervals, to create three rows and four columns. Then,
they will label each row with the numbers 1-3, and they will label each column with the letters A-E
using the sheets of paper. They should also label six “lines,” labeling lines 1-3 along three of the
columns and lines 4-6 along the three rows, as shown below.
4. Explain that each student in the group will map a line on this grid. Instruct each student to
determine the points they will be mapping. For example, if one student is assigned line 5, he
or she will be mapping the points A2, B2, C2, D2, and E2. Instruct students to write down their
assigned lines and all of their points on their Student Handouts.
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Steps for
what lies beneath?
5. Next, tell students that they will drill “core samples.” Ask students to think about what a core
sample might be. Then, explain that a core sample is a tube-shaped section of land that is
pulled out of the ground. When scientists look at the layers in the tube, they learn about the
layers of soil under Earth’s surface. Model taking a core sample so your students can see the
process. To do this, insert the clear plastic straw into a section of the soil, cover your finger over
the top of the straw, and then lift the straw out vertically. The photo below shows a straw with a
core sample.
Help students troubleshoot any problems they might encounter when they take their samples.
It may help to instruct students to use the straw as they would use a drill by twisting it into the
different layers using even and firm pressure.
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Steps for
what lies beneath?
6. Once all students have taken a core sample, they will create a cross-sectional map of their
line. You may need to explain the concept of a cross-sectional map. If so, see the background
information on the next page for more information. Students should create a cross-sectional
map of their line, showing the different layers, the approximate depths of each layer, and the
points where core samples were taken. The image below shows a sample cross-sectional map.
7. H
ave groups work together to see how the layers in the bin changed at different points along
the lines. Have each group come forward and describe the layers along the lines in their bins.
Encourage them to describe the layers that are present, the approximate depths of each layer,
and how the layers changed over the course of the lines.
8. Wrap-up Activity: Bring the class together to discuss the technique explored in this lesson. Have
students think about what information was represented by the cross-sectional map and why it
is important to make several cross-sectional maps for an entire area. Students should reflect on
the challenges in this experiment and propose modifications for future investigations. Finally,
have students think about what types of materials they would need to take larger core samples
from Earth’s surface. How would this process be similar to and different from the method in this
investigation?
What Lies Beneath? Extension Activities
1. Obtain soil profile maps of your town or region. Check your local library or http://soils.usda.gov/
gallery/state_soils/ to find soil maps. Then, challenge your students to use the maps to help
decide where different activities should take place. Students can work in groups to determine
appropriate locations for wells, extraction of mineral resources, and construction sites for
buildings. Students should justify their decisions based on the underlying soil types in the region.
2. H
ave students predict the layers of soil that are present in columns B and D on their grids. Then,
allow students to drill into these layers and check their predictions.
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what lies beneath?
Background Information
What is subsurface mapping?
Subsurface mapping is a method of representing the different layers beneath Earth’s surface.
A region can have several underlying soil and rock types, and subsurface mapping shows these
layers. Subsurface mapping involves the drilling of core samples. To obtain a core sample, a hollow
metal cylinder in drilled into Earth to a selected depth. The layers become stacked inside the
cylinder, and they offer a representative view of that section of land. For subsurface mapping to be
reliable and accurate, many samples must be taken across a broad field. Because the cross sections
are small, they are not harmful to the land. Core samples and subsurface mapping give geologists a
clear view of the composition of soil beneath Earth’s surface.
What is a cross-sectional map and how do I create one?
A cross-sectional map shows a section of something, as if it were cut straight through along an
axis. In this lesson, students will create a cross-sectional map of the different layers of soil in a
plastic tub. To create the cross-sectional map, they will first be assigned a line. It is along this line
that they will create their map, showing what the layers would look like if they sliced through the
tub along the line.
To create a cross-sectional map, you need several data points along an axis. In the case of this
lesson, your students will need data points from one line of a larger grid. You should discuss with
your students the idea that the cross section only shows one line. To gain a complete picture of
the subsurface, they must examine several cross sections, from along several different lines. A
more thorough understanding of the subsurface layers becomes evident when many lines of a
grid are mapped.
What are some of the different materials of rock strata?
People have long observed that Earth has many distinct layers. People first observed this in rock
outcrops (where many different layers of rock are visible). We now know that Earth’s crust is
composed of many different layers of rock. These layers are different from region to region, and there
is no set order of rock layers. The composition of layers of rock depends upon the parent material
(underlying rock) and historic events (such as ancient oceans, rivers, or volcanic eruptions).
In this lesson, students also examine different layers of soils, such as gravel, sand, or clay. As with
rock strata, these layers vary from region to region, depending greatly on the geography and
history of a region. An area with an old streambed, for instance, would likely have deeper layers of
gravel and sand than an area that has always been dry and desert-like.
What are some real-world benefits to knowing the subsurface rock strata?
In this lesson, students are challenged to identify some of the real-world applications of subsurface
mapping. Knowing what goes on beneath the surface can affect our lives on the surface. For one,
subsurface mapping can help identify aquifers or areas of water, and it can help us identify areas
suitable for wells. Second, subsurface maps and core samples can help us locate sources of natural
resources. These maps can help us locate resources like coal or oil, and they allow geologists and
miners to locate the exact location for a mine. Third, subsurface maps can help people identify
suitable locations for buildings and foundations. For example, an architect might hire a geologist to
analyze the subsurface of a hillside before building a house. If the map revealed a layer of clay, the
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Background Information
architect may opt to not build a house or to use a foundation set atop pillars drilled deep into the
earth because the clay layers can cause a hillside to slip or erode more quickly than other materials.
Key Vocabulary
core sample: a cylindrical sample of material lifted from beneath Earth’s surface that shows
different layers of rock and soil
cross section: an image produced by cutting straight through an object on an imaginary axis
subsurface mapping: the process of creating a map that shows the layers of underground rock and soil
strata: the layers of rock in the ground
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Teacher Handout
1. Write down your assigned line. What are all of the points along that line?
[Sample answer: I was assigned Line 4. I needed core samples from points A1, B1, C1, D1, and E1.]
2. Draw a picture to show your core sample. Label all of the different layers present in your straw.
[Images will vary.]
3. Once you have completed the cross-sectional map, describe the process you went through to
determine the different layers. In your answer, be sure to explain why having several core samples
was important.
[Sample answer: The core samples told us that the clay layer was really small and didn’t run all
the way across the tub. By having different core samples, we were better able to estimate what
was happening to the layers we couldn’t see. If we had only used one layer, we could have made
mistakes, like thinking the clay layer ran all the way across the tub.]
4. W
hat challenges did you face during this activity (in terms of taking the core samples and
creating the cross-sectional map)? How did you overcome those challenges?
[Sample answer: One challenge I faced was that the thickness of the amount of material in my
straw was less than the thickness of the tub. The straw compressed the layers. To solve this
problem, I measured the thickness of all the layers in the tub, and then estimated the correct
thickness of the layers in my straw.]
5. Work with your group to brainstorm at least three real-world uses for subsurface mapping. Write
the uses below.
[Sample answer: Subsurface mapping could help us know where to build large buildings. It could
also help us know where to find natural resources like oil or coal. It could also help us find water,
which would help us know where to drill a well.]
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Student Handout
Name:
Date:
1. Write down your assigned line. What are all of the points along that line?
2. Draw a picture to show your core sample. Label all of the different layers present in your straw.
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Student Handout
3. Once you have completed the cross-sectional map, describe the process you went through
to determine the different layers. In your answer, be sure to explain why having several core
samples was important.
4. What challenges did you face during this activity (in terms of taking the core samples and
creating the cross-sectional map)? How did you overcome those challenges?
5. Work with your group to brainstorm at least three real-world uses for subsurface mapping. Write
the uses below.
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