Download Seafloor Spreading Lab with Makeup

Names______________________________&_______________________________B___Date___
your name (first and last)
partner
Sea Floor Spreading Lab ES2 # 1
Purpose: Show rock age and magnetism patterns in spreading sea floor with a paper model.
Background: In the last few decades, scientists have discovered both age and magnetic patterns in the seafloor,
which are evidence for plate tectonics. These patterns show that new seafloor has been forming for millions of
years at mid-ocean ridges throughout the oceans. Magma melted within the crust rises to the seafloor, cools and
solidifies into new rock. In some places this new seafloor is spli t by movement of the asthenosphere under the
plates, forming two ocean crust which moves slowly from the ridge. Geologists call this seafloor spreading.
Elsewhere, one plate slides under another, or subducts, and deep ocean trenches are formed. Rock on the subducting plate becomes part of the asthenosphere. Oceanic crust is denser and thinner than continental crust, so
all seafloor rock is eventually destroyed in this way. Thus, the oldest seafloor rocks are only 180 million years old,
but the oldest continental rocks, which cannot be pulled into the trenches, are as old as 4,000 million years, or 4
billion years.
Pre-lab thinking. Read the Background above
1. What pulls the new seafloor apart in opposite directions?___________________________
2. Where are trenches formed?______________________
3. How old is the oldest seafloor?____________the oldest continental rocks?______________
Why are the continental rocks so old?
Procedure: Look at the diagram on p. 131 in text to see the model. Pull off pages 4 & 5 of your packet..
The black and colored stripes represent north and south paleomagnetism frozen into lava as it leaves the
mid-ocean ridge during sea floor spreading. The different colors represent rock ages.
1. Cut the color strip from p. 5 lengthwise and tape the orange ends together. Label the black stripes
“north” and the colored stripes “south”
(If no color printer, color the 4 sections of the rectangle as labeled, and put your name on the strips.
Color lightly, and don’t take too long, it needn’t be perfect. Tape the orange ends together and label
stripes as above.
2. Fold pg. 4 lengthwise. Cut slits A, B & C in the center, but not out to the edges. Flatten the paper
3. Put the “start” ends of the colored strip together, and pull them up through center slit B, like lava
erupting from the mid-ocean ridge. Pull the sides, like new sea floor, towards slits A and C. Insert the
ends in slits A and C like oceanic crust subducting at a deep ocean trench. Practice moving the strips
until you can make the two ends of the strip come up through B and subduct at A and C at the same
speed.
Analyse 1. Is the rock represented by the orange strip the oldest or youngest?_________________
MU (only do if incorrect on or missed original question) Explain how you know:
2. Is the mid-oceanic ridge at SLIT B or SLITS A& C? ________
Circle one: At this boundary are plates coming together or pulling apart?
Is this called converging or diverging?_______________
MU Explain how ridge is formed:
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3. Is the rock represented by the blue strip the oldest or youngest?____________________
MU Explain how you know:
4. Is the subduction zone with ocean trenches at SLIT B or SLITS A& C? _______
Are the plates at this boundary converging or diverging? _____________
MU Explain how trench is formed:
5. New seafloor rock is continually being formed at mid-ocean ridges and destroyed at trenches in
subduction zones. Rock is formed on the continents, but then pushed up into mountains. Which
rock will be older, continental or ocean floor?________________
MU Explain why:
6. Ocean plates slide under continental plates.
Which are denser, oceans or continents? ________________ Which are thicker? ______________?
MU Give average thickness of each with measurement unit (use textbook if needed):
7. Pick a color for convergent boundaries and use it on the symbol on the map key at the bottom of page 3. Color
all convergent boundaries that color on the map. Are the plates coming together, spreading apart or sliding by
each other?__________
Look at the diagram on p. 134.
4 of these features are formed at convergent boundaries. Circle them:
volcanic islands
trench mid-ocean ridge
new sea floor
volcanic mountain chain
rift valley
non-volcanic mountain range
MU Explain how two are formed--7a:
MU Explain how two are formed--7b:
8. Repeat step 7 for divergent boundaries.
Are the plates coming together, spreading apart or sliding by each other?__________
3 of these features are formed at divergent boundaries. Circle them:
volcanic islands
trench mid-ocean ridge
new sea floor
volcanic mountain chain
rift valley
non-volcanic mountain range
MU Explain how two are formed--8a:
MU Explain how two are formed--8b:
9. On the map, color the transform boundaries a third color and mark it on the map key.
Are the plates coming together, spreading apart or sliding by each other?_________
Earthquakes happen at transform boundaries. At what other boundary types do they occur? ____________________ & ______________________ MU Explain cause of earthquakes--see text and notes
Look at diagram 24 on p. 134, and read the paragraph on transform boundaries. What is caused by the plates rubbing together?____________________
10. What kind of mountains are formed when from the magma when 2 pieces of ocean crust separate, volcanic, or non-volcanic?_____________________
MU Explain why:
Label the Mid-Atlantic Ridge, and Iceland on your map. What kind of boundary is this, divergent or
convergent?_____________________ MU Explain how you know
11. Why are the magnetic stripes on the ocean floor the same on either side of the mid-ocean ridge? (see p. 126)
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Key: color divergent, convergent,
and transform each
a different color,
here and on map
Connect boundaries where possible.
Compare to map on p. 133
Key: don’t color complex or uncertain
boundaries
Name_______________________
Give a new fact you learned, or question you still have about seafloor spreading:
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continent
Names______________________&________________________
fold along line
slit A
slit B
slit C
continent
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start start
Name_____________________
blue blue
green
green
yellow
yellow
orange
orange
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