Download Why is there Lithosphere?

Why is there Lithosphere?
STUDENT PAGES
Procedure
“upper mantle.” The warm chocolate bar will be
referred to as a portion of the asthenosphere.
The asthenosphere is also part of the mantle.
So, now you know what each of the 3 layers of
your model represents.
Follow the steps below while taking notes in your
science notebook.
1.
Your teacher will provide each student group
with two small, square chocolate candy bars and
a graham cracker. Do not eat the materials
(yet!), and leave the wrappers on the chocolate
bars.
A volunteer must agree to sit on one of the
chocolate bars (wrapper on) for about 10
minutes.
a.
a.
5. The lithosphere is the outer portion of the
Earth comprised of the crust and upper mantle.
a.
What is the purpose of sitting on one of the
candy bars?
6. After about 10 minutes, the chocolate bar
should be warm enough for the activity. With
clean hands, unwrap both chocolate bars and
construct your proposed model.
2. Before removing the candy bar from under the
volunteer student, consider how these three
items (cracker and two chocolate bars) can be
arranged to model the outer portion of the
earth (i.e., excluding the outer and inner core).
Remember that the two chocolate bars have the
same composition.
READ THIS NEXT PARAGRAPH BEFORE YOU
BEGIN TO APPLY STRESS TO YOUR MODEL!
Your teacher will show on the overhead projector
the proper way to work with your model. One
student should hold the model in two hands in front
of him/her so everyone in the group can observe.
Slowly and carefully apply downward stress to the
edges and upward stress to the center.
When any portion of the model breaks – or
fractures – STOP applying the stress.
Draw your model in your science notebook.
Shade and label the different layers,
according to the different compositions.
3. The cracker represents the earth’s oceanic
crust and both chocolate bars are the mantle –
because they have the same composition.
a.
Of the three layers, where would the
warmest layer be located?
a.
b. Why?
c.
Which layer or layers represent(s) the
lithosphere?
b. Place a bracket } on your drawing next to
the layers that represent the lithosphere.
b. Why don’t we just heat the candy bar in the
microwave?
a.
Revise and label your initial drawing to
reflect these new observations. Labels
should show the earth layer represented
(not the type of candy bar).
Where should the room temperature
chocolate bar be located?
Draw what you observe in your science
notebook. Label this drawing with
appropriate terms for the layers and title it
as “Post-Stress.”
7. Use your observations of the model to answer
the following questions.
4. The room temperature chocolate bar represents
the uppermost portion of the mantle, or the
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Why is there Lithosphere?
STUDENT PAGES
a.
Which Earth layer or layers fractured when
stress was applied (NOTE: Use the Earth
layer terms, not “cracker” or “chocolate
bar”)?
c.
Compare your group’s results with results of
other student groups. Were any other
results different?
9. Why do you think geologists group the crust and
upper mantle together as the lithosphere, when
each layer is made of different materials?
b. Which layer or layers did not fracture?
c.
Which layer or layers would you consider to
be rigid and brittle?
10. Stress causes fracturing of the brittle
lithosphere. These broken pieces of lithosphere
are called plates, or lithospheric plates.
Continued stress (and other factors that won’t
be described here) cause plate motion. Because
of the rigid nature of the lithosphere, plates
move independently of the underlying plastic
asthenosphere.
8. The term plastic texture of solid rock means
that it has the ability to move or flow when
stress is applied. In other words, the rock is
not liquid, but it is still able to flow, because it
has a plastic texture. The layer of the mantle
that is plastic is called the asthenosphere. The
top of the asthenosphere lies approximately
between 100 and 200 km below the earth’s
surface. Geologists are uncertain where the
base of the asthenosphere is located, but
estimates are that it extends to a depth of
between 600 and 700 km. In other words, the
asthenosphere is NOT the remainder of the
mantle, but is just the hot, plastic portion of
the mantle below the lithosphere.
a.
a.
How many lithospheric plates are illustrated
in your Post-Stress drawing?
11. Review figures of the lithosphere and
asthenosphere from texts, web sites, or CDROMs and compare them to your model.
12. Discuss the results of applying stress on the
lithosphere and asthenosphere, based on your
observations of the model.
Which layer or layers would you consider to
be the asthenosphere with its plastic
texture?
13. If your teacher gives permission, and you have
been handling the model with clean hands, it is
now okay to eat the Earth model.
b. Add the term asthenosphere to your
diagram.
Summarize your observations and discoveries by
answering the questions on the next page.
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Why is there Lithosphere?
STUDENT PAGES
Questions
1.
Draw a side-view (called a cross-section) of the lithosphere and asthenosphere. Label the tectonic
layers. Also, label the individual layers of the cross-section.
2. Why does the upper mantle fracture differently from the mantle below it?
3. How do the differences in texture of the mantle and the crust relate to the formation of lithospheric
plates?
4. Are the upper mantle and mantle below it the same composition?
5. Write a one-paragraph summary of how the different textures of the mantle affect the formation of
lithosphere and asthenosphere. Include why the mantle has different textures.
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