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Magnetic Evidence for Seafloor Spreading Quiz
1) How do scientists determine the age of a seafloor basalt?
a) They can get a radiometric age if they can collect a sample.
b) They can use the time scale for magnetic reversals.
c) They can look at fossils in the sediments on top of the basaltic rocks.
d) All of these.
2) What is true about the seafloor near mid-ocean ridge?
a) Rocks are younger closer to the ridge.
b) The crust is thicker near the ridge.
c) The magnetic stripes are thinnest near the ridge and get thicker with distance away
from the ridge.
d) All of the above.
3) Submarines during WWII discovered the magnetic patterns on the seafloor.
a) True
b) False
4) The magnetic stripes on either side of the mid-ocean ridge, the same distance out
from the ridge, have opposite polarity.
a) True
b) False
5) With increasing age, seafloor rocks
a) Wear away to become thinner.
b) Become hotter.
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c) Collect an increasing amount of sediment on top.
d) All of these.
6) The oldest seafloor is less than 180 million years old.
a) True
b) False
7) What is not true about the magnetic stripes on the ocean floor?
a) Stripes alternate, normal and reverse polarity, across the ocean floor.
b) Stripes indicate the age of the basaltic rock.
c) Stripes are evidence of apparent polar wander.
d) Stripes end abruptly at the edges of continents.
8) Navy ships use these to search for enemy submarines, but accidently discovered
the magnetic polarity of the seafloor.
a) Bar magnets
b) Magnetometers
c) Electromagnets
d) Echo sounders
9) Observations of the seafloor support the idea that new seafloor is created at midocean ridges.
a) True
b) False
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10) If it is true that new seafloor is created at mid-ocean ridges, then
a) The planet must be getting bigger.
b) Old seafloor must be destroyed somewhere.
c) New seafloor must sink directly into the mantle.
d) None of these.
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