Download 3.5 Seafloor Spreading

Seafloor Spreading
Geo 12
Name______________
For each of the following, indicate the correct response for the multiple choice questions below.
1. Polarity reversals on Earth are believed to be related motion in the:
a) Lithosphere b) crust
c) inner core d) mantle
e) outer core
2. Magnetic minerals in basalts of the same age on the same continent:
a) point in opposite directions b) point in the same direction c) are always positively or normally
polarized
d) are always negatively or reversely polarized
e) none of the above
3. When the magnetic field of the Earth is reversed:
a) the Earth flips over so that the North Pole becomes the South Pole b) Earth alters its direction of
rotation from counter-clockwise to clockwise c) the north-seeking end of a compass would point
toward the south magnetic pole
d) all existing basaltic rocks in the ocean would reverse their
polarity
e) all the above
4. The pattern of magnetic anomalies on the ocean floor resembles:
a) a series of points of positive and negative anomalies b) discontinuous stripes of various lengths and
widths perpendicular to the ridge
c) parallel stripes symmetrical about the ridge axis
d) stripes of equal width parallel to the ridge axis
e) none of the above
5. If the Earth’s magnetic field did not occasionally reverse polarity:
a) compasses would not work b) magnetic stripes would not be produced on the sea floor
c) apparent polar wander curves would not exist
d) the North Pole would become the South Pole
more frequently
e) continents would never have moved
Answer the following questions with written responses.
6. Why is apparent polar wandering called “apparent”?
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Use the figure 19.15 below that depicts the periods of normal and reversed polarity on Earth during the
past 5 million years to answer the following questions.
7. How many periods of normal polarity has the Earth
experienced in the last 5 million years?
8. How many periods of reversed polarity has the
Earth experienced in the last 5 million years?
9. What is the name given to the period the Earth is
presently experiencing? Is this period characterized by
normal or reversed polarity? For how long has the
Earth been in this period?
10. Is there a pattern to the data represented on
figure 19.15? Or do polarity reversals appear to be
random? Explain your reasoning.
11. Was the Earth experiencing a norm or reversed
polarity?
i) 2 million years ago (M.Y.A)
ii) 3 M.Y.A
iii) 4 M.Y.A
Use figure 19.17 to answer the following questions.
12. How old are the oldest rocks in the Atlantic Oceans?
13. Where are these rocks located in relation to the Atlantic mid-ocean ridge?
14. Where are the youngest rocks located in the Atlantic Ocean in relation to the mid-ocean ridge?
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15. Using the following terms, explain the pattern of the ages of the ocean floor rocks in the Atlantic
Ocean:
Mid-ocean ridge
basalt
lava
Volcanism
age
ridge axis
Seafloor spreading
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