1. Describe the landscape of the ocean floor.
2. (a) What is the Mid-Atlantic Ridge?
(b) What is the relationship between an ocean
ridge and an ocean trench?
3. What new technologies allowed scientists to
confirm that the sea floors are spreading?
4. Hess hypothesized that new sea floor was
produced at ocean ridges.
(a) Why are deep ocean trenches important to
his hypothesis?
(b) What would happen to the dimensions of
Earth if the sea floor did not descend into
the mantle at ocean trenches?
5. Which layers of Earth are involved in sea-floor
spreading?
A. crust and core
B. core and mantle
C. crust and asthenosphere
D. lithosphere and asthenosphere
6. (a) List the sources of heat within Earth.
(b) How does this heat contribute to mantle
convection?
7. How do convection currents in the mantle
contribute to sea-floor spreading?
8. Why does the sea floor bulge up at a spreading
ridge?
A. Rising mantle pushes up on the crust.
B. Magma piles up as it rises from the mantle.
C. Heated crust is less dense, so it floats higher.
D. Friction curls up the edges of the crust as it
moves.
9. Explain how the magnetic orientation of lava
layers demonstrates reversals of Earth’s
magnetic field.
10. Describe how each of the following was used to
argue that the sea floor is spreading.
(a) magnetic reversals
(b) age of rocks
(c) mid-ocean ridges
(d) deep ocean trenches
11. What evidence shows that the rock further from
ocean ridges is older than rock closer to the
ridges?
12. The colour coding in Figure 4 shows the age of
the sea floor around the Juan de a spreading
ridge.
(a) Which colour represents the current
location of the spreading ridge?
(b) The white regions indicate rocks with
reversed magnetic polarity. Explain how the
age and polarity of the rock suggests the
ocean floor on either side of the ridge has
moved.
(c) In what direction is the sea floor spreading?
How do you know?
2 answers
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