Download CONSTRUCTING A SEA-FLOOR SPREADING MODEL

Name _________________________________________ Date __________ Period _________
CONSTRUCTING A SEA-FLOOR SPREADING MODEL
PURPOSE: To demonstrate processes and features at mid-ocean ridges and at trenches.
BACKGROUND INFORMATION:
The lithosphere is composed of the crust and upper mantle and is broken into large pieces
know as plates. The lithospheric plates, carrying both oceanic and continental rock, “float” on the
plastic part of the mantle below the lithosphere. Plates move together, separate, and slide past each
other creating regions of volcanic activity, mountain building and earthquakes. The plates are
thought to be driven by a convection current mechanism that is deep within the earth.
Rocks in the ocean basins are younger than the Paleozoic Era. Sea-floor spreading was
suggested to account for this age. The sea floor is spreading from the ocean ridges where new
ocean crust is created and spreads outward. Rocks directly next to the ocean ridges on either side
are younger than the rocks farther away. The youngest rocks are in the center of the ridges. A great
deal of activity—volcanoes, earthquakes, fault zones, trenches—take place along these ridges.
The concept of sea-floor spreading was devised to explain the lack of very old (Pre-Cambrian
and Paleozoic) oceanic crust. It is now generally accented as part of the driving mechanism for plate
tectonics. According to this concept, the lithosphere is being pulled apart by forces deep within the
Earth, possibly creating convection currents, resulting in large fractures. Partial melting then occurs,
producing magma. This magma rises to the surface “filling in” the gaps left by the pull-apart
fractures and solidifies, forming new oceanic crust. This process continues and even newer magma
rises to the surface, filling in the most recent fracture. This results in an ocean floor which has
formed over several million years. The youngest or newest part of the ocean floor is at the spreading
center. As we move away from the spreading center in either direction, the ocean floor located
farthest from the spreading center.
PROCEDURES:
1. Cut along the lines indicated on the Sea-Floor Model
worksheet that accompanies this activity. Color the areas
indicated on the two strips.
2. Tape together the red ends of the strips. Fold this one
long strip in half at the taped seam, with the colored
portion on the inside.
3. Pull the loose edges of the colored paper strip up through
the Slit B of the uncolored, larger piece of the worksheet. Pull
one end of the strip down through Slit A and one end through
Slit C. See the sketch below.
4. Practice moving the colored paper strips through the slits so that
the same color “emerges” from Slit B at the same time, and the
same color “disappears” from Slits A and C simultaneously.
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DISCUSSION QUESTIONS/CONCLUSTION: (10 pts each)
1. What do the strips represent?
2. What do the colors of the strips represent?
3. What kind of plate boundary does Slit B represent?
4. What Earth feature forms at Slit B?
5. What kind of plate boundary do Slits A and C represent?
6. What Earth feature forms underwater when an oceanic plate slides under a continental plate?
7. If you were to sample and date the rocks along the colored strip starting at Slit B and moving
toward Slit A, what change, if any, would you observe in the age of the rocks?
8. If you were to sample and date the rocks along the colored strip starting at Slit B and moving
toward Slit C, what change, if any, would you observe in the age of the rocks?
9. New seafloor rock is continually being formed at mid-ocean ridges and old seafloor is continually
removed at ocean trenches. If the rock on the continents is continually formed but not removed,
how would the age of the oldest rocks on the continents compare with the age of the oldest rocks
on the seafloor? Do not use the words it or they, be specific.
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SEA-FLOOR MODEL WORKSHEET
_________________________________slit A
red
red
orange
orange
yellow
yellow
green
green
____________________________________slit B
_________________________________________slit C
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