Section #: 17.2
Seafloor Spreading
Practice Test
1.
The thickness of ocean sediments that are close to a mid-ocean ridge is __________ the thickness of ocean sediments that are far from mid-ocean ridges.
a.
the same as
b.
always 100 times
c.
less than
d.
more than
Hint
2.
What is an isochron?
a.
a line on a seafloor map that connects points of equal elevation
b.
a line on a seafloor map that connects points of equal age
c.
a point on a seafloor map that has a magnetic reversal
d.
a part of a mid-ocean ridge
Hint
3.
What is the polarity of a magnetic field that has the same polarity as the present magnetic field?
a.
a magnetic reversal
b.
an isochron
c.
a normal polarity
d.
a reverse polarity
Hint
4.
According to the data shown in the figure, what was Earth's magnetic polarity like 5 million years ago?
a.
the same as today
b.
the reverse of today
c.
there was no magnetic field
d.
pointing in an east-west direction
Hint
5.
What two topographic features of the ocean floor were discovered only with the use of sonar?
a.
volcanic islands and mid-ocean ridges
b.
mid-ocean ridges and deep-sea trenches
c.
shallow-sea trenches and volcanic islands
d.
mid-ocean ridges and earthquakes
Hint
6.
What is the study of Earth's magnetic record?
a.
paleogeography
b.
magnetometer
c.
paleontology
d.
paleomagnetism
Hint
7.
Rocks close to mid-ocean ridges are __________ rocks far from mid-ocean ridges.
a.
older than
b.
the same age as
c.
younger than
d.
a different composition than
Hint
8.
What causes the seafloor to spread?
a.
rising molten magma
b.
drifting continental crust
c.
sinking magma
d.
earthquakes
Hint
9.
Harry Hess' theory of __________ explained how ocean crust is generated and destroyed.
a.
continental drift
b.
seafloor spreading
c.
plate tectonics
d.
continental movement
Hint
10.
An expedition finds a sample in the rock on the seafloor thought to be 4 million years old. What was the polarity of the Earth at that time, according to the figure?
a.
normal
b.
reversed
c.
nonexistent
d.
half-reversed
Hint
11.
An expedition brings up a piece of rock from the Gauss normal epoch. According to the figure, what is the probability that it came from a time when the magnetic field is the same as today?
a.
highly unlikely
b.
unlikely
c.
likely
d.
very likely
Hint
12.
A __________ is a device that can detect changes in the strength of the magnetic field.
a.
satellite
b.
magnetometer
c.
sonar
d.
GPS
Hint
