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HANDOUT B
WEGNER’S PROOF: Plate Tectonics; How Sweet it Is!
PRE LAB DISCUSSION and REVIEW
The theory of Plate Tectonics proposes that the Earth’s crust is made up of nine to
fifteen large, major plates and several smaller ones. The Earth is not one large solid
piece, as most people think.
The plates move very slowly across the upper part of the mantle,where they float on a
layer called the asthenosphere. This layer is thick, extremely hot and plastic-like.
The edges of the plates are referred to as plate boundaries. The Plate Tectonic theory
proposes that three types of movements occur at the plate boundaries as the plates
move: convergent, divergent and transform. Subduction occurs where two plates
of unequal density converge, with the denser plate sinking under the less dense plate.
Below is an example of a cross section diagram:
PURPOSE:
1. To represent the natural world using models to demonstrate interactions of
movement at plate boundaries.
2. To identify the strengths and the limitations of using models to explain how the
Earth’s surface has changed over time and to help predict how it will continue to
change.
MATERIALS: For Group of Two
1. Blue cake icing (approximately ½ cup)
6. One plastic cup
2. Two Graham Cracker squares
7. 12” by 12” sheet of wax paper
3. Two chewing gum squares
8. Wet wipes
4. One plastic knife
9. Disposable aprons
5. Small bottle of water
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PROCEDURE:
1. Before putting your wax paper on the table, place a few drops of water on the table
in order to keep the paper from sliding.
2. Use the knife to spread the frosting to the outer edges of the wax paper, making the
layer about two times as thick as a Graham Cracker. Refer to the picture (Set Up)
provided on Handout B --- Lab Diagram.
3. Place two squares of chewing gum in their wrappers side-by-side lightly on top of the
frosting so that they are touching; press down as you slowly push them apart (about ¼
of an inch). Observe what happens to the frosting where the plates are separated. On
the Data Sheet for Handout B draw a cross section diagram (NOT a replica of what
is on the Lab Sheet) to show what the divergent plate boundary looks like and answer
the questions. Remove the two pieces of chewing gum, scrape off the frosting and
smooth the frosting back onto the wax paper. (refer to the Handout B --- Lab Diagram
#1)
4. Break a whole Graham Cracker into two squares. Place one Graham Cracker
square lightly onto the frosting. Place one of the chewing gum squares next to the
Graham Cracker square so that they are almost touching. Gently push the Graham
Cracker square toward the chewing gum until the two overlap and the Graham Cracker
is on top (refer to Handout B --- Lab Diagram #2). On the Data Sheet for Handout B
draw a cross section diagram to show what a Continental-Oceanic Convergent
Boundary (subduction) looks like and answer the questions.
5. Remove both the Graham Cracker and the chewing gum from the frosting. Scrape
off the frosting from both the cracker and the chewing gum and smooth the frosting back
onto the wax paper. Place a smooth edge of both crackers into the cup of water for five
seconds. (refer to the Handout B --- Lab Diagram #3). Place the crackers with the
wet edges next to each other on the frosting. Slowly push the Graham Crackers toward
each other. Observe the edges of the Graham Crackers where they are colliding. On
the Data Sheet for Handout B draw a cross section diagram to show what a
Convergent Continental-Continental Boundary looks like and answer the questions.
6. Remove the two Graham Crackers from the frosting and turn them around so that
two dry edges are next to each other. Gently push them together, applying steady
pressure; at the same time, push one piece away from you and pull the other toward
you. If you do this correctly, the Graham Crackers should initially hold along the edges;
as you increase the push/pull pressure, the edges will eventually crumble due to the
opposing forces. On the Data Sheet for Handout B, draw a cross section diagram to
show what a Transform Plate Boundary looks like and answer the questions (refer to
Handout B --- Lab Diagram #4).
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