Download Sea Floor Spreading LAB 2017

Name _____________________________________________________
Lab Group Members ________________________________________ , ______________________________
___________________________________________ , ____________________________________________
Date ______________________
Lab # ________________
The Theory of Plate
Tectonics and Sea Floor
Spreading
Modeling Seafloor Spreading Occurring at Mid Ocean Ridges
Introduction:
A map of the ocean Seafloor shows a variety of topographic features: flat Abyssal plains, long
mountain chains called ridges, and deep ocean trenches. Today we know that Mid-Ocean Ridges are
part of chain of mountains some 84,000 km long and the Mid-Atlantic Ridge is the longest mountain
chain on Earth but these are relatively new discoveries.
Geologist Harry Hess, while serving in the U.S. Navy during World War II began mapping out
the oceans floor using a new tool called sonar, which was developed originally to find hidden
submarines. His research during and after the war helped Hess to develop a revolutionary theory that
later would be called Seafloor Spreading.
Through direct sampling, Hess measured the age of the sea floor and realized that new seafloor has
continually been forming over millions of years at the mid-ocean ridges. Hess found that on each side
of the ridge, sea floor got older as a person moved away from the ridge towards the continents. The
older, denser oceanic crust eventually descends into deep trenches along the continents and is recycle,
this is called Subduction.
The deep sea trenches are long, narrow basins which extend 8-11 km below sea level. Trenches
develop at subduction zones, where denser oceanic lithosphere slides back into the mantle under the less
dense continental crust. The oldest seafloor rocks are only about 180 million years old compared to the
oldest continental rocks, which can be as old as 4,000 million years.
Pre Lab:
1. In the diagram above,
 highlight both the word Mid-ocean ridge and the ridge. Label this plate boundary.
 highlight both the word Ocean trench and the trench. Label this plate boundary.
 Using a highlighter, draw in the convection currents in the asthenosphere.
2. Describe what Hess found when he scanned the ocean floor with sonar.
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3. Describe what Hess found when he measured the age of the sea floor.
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Objective:
To construct a paper model that will illustrate
how the seafloor is created at mid-ocean ridges
and is recycled where it descends into trenches.
Materials:
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Colored Pencils
Scissors
Tape
Procedure: Follow the steps in order, check off each step as you complete it.
1. Tear off the past page and color the strips with colored pencils.
2. Cut the strips out after coloring. Tape the end of one strip at blue end to the other strip at the
blue end. It helps if you make sure the colored sides are touching/ facing each other, blue to
blue, orange touching orange etc.
3. On the lab page Labeled “Sea Floor Diagram”, fold and cut along the short dotted lines.
4. Thread the two ends of your strip of paper through Slit B.
5. Pull one side down through Slit A and the other through Slit C, color side up
6. Pull the strips through the slits so that the same colors on both strips come out from Slit B and go
into or disappear into Slits A and C at the same time.
Label your Sea Floor. Check off each item below as you label it.
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Label the Mid-Atlantic Ridge/ Mid Oceanic Ridge
Record the relative age of the rock found here. (older vs younger)
Name the type of tectonic boundary found at this ocean ridge (use ESRT pg5)
Label the Deep Sea Trenches
Record the relative age of the rock found here. (older vs younger)
Name the type of tectonic boundary found at a zone of Subduction (ESRT pg5)
Record the density of the Ocean Crust
Analysis:
1. Explains what happens at Slit B? _____________________________________________________
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2. Name the land feature occurs at this location on the seafloor. __________________________________
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3. What happens to the tectonic plates at Slit B? (Circle one)
Divergence / Subduction
4. Explains what happens at both Slit A and C? _______________________________________________
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5. What land features occur where sea floor is pulled under continental crust? _______________________
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6. What happens to the crustal plates at Slit A and C? (Circle one)
Divergence
7.
Subduction/
If you were to start sampling and date the rocks along the colored strip starting at Slit B and move
outward towards Slit A or Slit C, explain what changes would you see in the age of the rocks.
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8. Why is it important that your model have an identical color patterns on both sides of the center slit?
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9. What is something that could possibly cause the plates to be pulled apart at the Mid Ocean ridge?
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Conclusion:
Briefly stated in your own words: What is Sea Floor Spreading? Make sure you include in your summary
data that helped Harry Hess his develop his theory.
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SEA FLOOR DIAGRAM
Land feature formed at slit A is a ____________________________
Here, ocean crust is formed a ____________ time ago so the rock age is
very ___________________
This is a _________________________________ Plate Boundary
where subduction occurs.
Land feature formed at slit B is a ____________________________
Here, ocean crust is formed a ____________ time ago so the rock
age is very ___________________
This is a _________________________________ Plate Boundary
where sea floor spreading occurs.
.
Land feature formed at slit C is a ____________________________
Here, ocean crust is formed a ____________ time ago so the rock age is
very ___________________
This is a _________________________________ Plate Boundary
where subduction occurs.