Activity 6
Lesson Topic: The Physical Setting: Processes that Shape Earth
Objectives: To acquaint students with the concept of plate tectonics.
Introductory Information: The surface of the earth is always shifting and moving. This
movement causes stress on the Earth’s crust, allowing rocks to fracture, fault, or fold.
Fractures are large cracks in the Earth’s surface while faults are when rocks break and
then slide against one another.
Normal Fault
Reverse Fault
Thrust Fault
All of this activity occurs within the Earth’s rock mantle which is made liquid due to the
intense heat from the Earth’s core. The crust then moves over the mantel and has
fractured into seven major tectonic plates, which collide and grind past each other.
Tectonic plates are responsible for the creation of mountains, volcanoes, and earthquakes.
The oceanic plates are mostly made of dense basaltic rock and the continental plates are
mostly made of lighter granitic igneous, sedimentary, and metamorphic rocks. When an
oceanic plate collides with a continental plate, it is often pushed beneath the continental
plate. This is known as subduction. This subduction process carries the rock to increased
temperature and pressure zones within the earth’s crust and mantle, and eventually causes
the rock to become molten magma. New sources of volcanic or intrusive igneous rocks
can form from the material to begin another process in the rock cycle.
Activity 6
When looking at the map of the world for example, it is often observed that the
continents appear like they could fit together like pieces of a jigsaw puzzle. Geologic
discoveries have thus found that although the continents may seem fixed in one place,
they were not always where they are located today. The implication that al the continents
were once joined as one supercontinent is known as Pangaea, and it is because of plate
tectonics: the fracturing, faulting, and slow movement over time that has shaped the
Earth’s crust into how we are familiar with it today.
NCTM Content Standard Objectives:
 Earth and Space Sciences
o
The Nature of Science
o
The Physical Setting
o
Historical Perspectives
Ohio Science Academic Content Standards: Students demonstrate an understanding
about how Earth systems and processes interact in the geosphere resulting in the
habitability of Earth. In addition, it includes understanding the properties and the
interconnected nature of Earth’s systems, processes that shape Earth and Earth’s history.
Note to Educators: This activity has two similar but different sub-activities concerning
plate tectonics. Four additional worksheets and five transparencies can further be used to
aid in a classroom activity/discussion concerning plate tectonics and Pangaea.
Activity 6
Activity 6A: Plate Tectonics with an Orange
Materials:
 Oranges (one for each student, or they can work in pairs)
 Clay or play dough (optional)
 Toothpicks
Instructional Strategy: Have students peel an orange without using a knife and by
creating as few pieces as possible. The peel represents the earth’s crust and the crust is in
pieces. Then have the students lay the orange peel on their work surface and record their
observations. Finally, tell the students to replace the peel back onto the orange, securing
the peel in place with the toothpicks. Option: Since the fault lines on the earth’s crust
are not visible, students may wish to roll out thin pieces of clay or play dough to cover
the cracks in the peel pieces that are replaced over the orange.
Topics for Discussion:
1. The earth is spherical like the orange although it is often difficult to see this
roundness of the earth except from space.
2. What did the students observe when the orange peel was laying on their work
surface? Did they notice that the pieces flattened out?
3. When the peel is back on the orange, how does this represent the earth’s crust?
What do the cracks represent?
Activity 6B: Milk Chocolate Movement
Materials:
Any type of popular candy bar that has several layers
“Milk Chocolate Movement” Worksheet to record observations
Instructional Strategy: Use a plastic knife to make 2-3 cracks across the middle of the
candy bar. The cracked chocolate layer represents the plates of the earth’s lithosphere.
Stretch the candy bar, pulling it apart just a little. The exposed caramel represents the
new material that rises to form new crust (divergence). Then, push the candy bar back
together. Add pressure to form “mountains”. Then, slide one chocolate “plate” beneath
another (convergence). Continue to push and pull to observe the movements of the plates
and the effects this has on the surface of the earth. Have students draw/record their
observations on the “Milk Chocolate Movement” worksheet provided.
Activity 6
Milk Chocolate Movement
What’s Happening?
2-3 cracks are being made across
the middle of the candy bar.
The candy bar is being pulled apart,
slowly stretching plates away from
each other (divergence).
The candy bar is being pushed back
together with enough pressure to
form “mountain”-like bumps, and
sliding “plates” together
(convergence).
What happens to the candy bar as
this cycle happens again?
Draw/Record Your Observations