Earth’s Structure
http://www.brainpop.com/science/earthsystem/earthsstructure/
Label the structure as you watch the BrainPop video.
Why is the Atlantic Ocean Expanding?
You receive an e-mail with the subject, “The Atlantic Ocean is expanding!” Thinking this
e-mail is very strange, you begin to read it:
Dear Earth Science Student,
According to our research at the United States Geological Survey (or
USGS), the Atlantic Ocean is getting bigger, and we don’t know why! There
is something “strange” happening on the ocean floor near the mid-ocean ridge.
We heard that you are currently studying plate tectonics in earth science
class, and we were hoping that you’d be able to help us out.
John Johnson
Head Scientist, United States Geological Survey
Since you have been learning about plate tectonics, you decide to offer your help. You
borrow a deep-sea exploring vehicle called Alvin to explore the mid-ocean ridge located
in the middle of the Atlantic Ocean. The mid-ocean ridge is the largest mountain range
in the world and is formed when two oceanic plates are diverging in the middle of the
Atlantic Ocean.
On your trip you make the following observations:
1.
When you reach the mid-ocean ridge, you see signs of volcanic
activity. The magma seems to come out of the mid-ocean ridge, cool,
and form new rock.
2. Looking at the plate boundary between North America and the Atlantic
Ocean, you see the ocean floor entering a deep ocean trench beneath
the continental crust of North America! As you recall from our plate
boundaries activity, this process is called subduction. The location
where subduction occurs is called a subduction zone
Using the magnetic stripes diagram below, make two additional observations:
1.
Examine the map indicating the age of the rocks
around the mid-ocean ridge. What pattern(s) do you
notice?
Examine the map that indicates the polarity of the
rocks around the mid-ocean ridge. What pattern(s) do
you notice?
Using your observations, answer the following questions:
What do you think is causing the ocean floor to increase in size?
Why do you think the rock farther from the mid-ocean ridge is older than the rock near
the mid-ocean ridge?
How do you think subduction affects the size of the Atlantic Ocean?
What do you think is going to happen to the crust once it enters the deep ocean trench?
Why is the Atlantic Ocean NOT expanding at the same rate that the new crust is being
made? (It is increasing in size, but the rate of growth is MUCH LESS than the rate that
new rock is formed at the mid-ocean ridge. How can you explain this?)
Answer the questions below:
a. Have your answers to the previous questions changed after building a
model?
b. Why do you think it is important to construct models?
c. Write a response to the original e-mail with your findings.
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