Earth Science: Geology, the Environment, and the Universe

Section 2: Seafloor Spreading

Seafloor Spreading

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)more than
B)the same as
C)always 100 times
D)less than
2
What causes the seafloor to spread?
A)sinking magma
B)rising molten magma
C)earthquakes
D)drifting continental crust
3
Harry Hess' theory of __________ explained how ocean crust is generated and destroyed.
A)continental drift
B)continental movement
C)seafloor spreading
D)plate tectonics
4
What two topographic features of the ocean floor were discovered only with the use of sonar?
A)shallow-sea trenches and volcanic islands
B)volcanic islands and mid-ocean ridges
C)mid-ocean ridges and earthquakes
D)mid-ocean ridges and deep-sea trenches
5
What is an isochron?
A)a line on a seafloor map that connects points of equal age
B)a point on a seafloor map that has a magnetic reversal
C)a line on a seafloor map that connects points of equal elevation
D)a part of a mid-ocean ridge
6
What is the study of Earth's magnetic record?
A)magnetometer
B)paleogeography
C)paleomagnetism
D)paleontology
7
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?
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A)very likely
B)unlikely
C)likely
D)highly unlikely
8
According to the data shown in the figure, what was Earth's magnetic polarity like 5 million years ago?
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A)there was no magnetic field
B)the reverse of today
C)the same as today
D)pointing in an east-west direction
9
Rocks close to mid-ocean ridges are __________ rocks far from mid-ocean ridges.
A)younger than
B)a different composition than
C)older than
D)the same age as
10
A __________ is a device that can detect changes in the strength of the magnetic field.
A)GPS
B)sonar
C)magnetometer
D)satellite
11
What is the polarity of a magnetic field that has the same polarity as the present magnetic field?
A)an isochron
B)a magnetic reversal
C)a normal polarity
D)a reverse polarity
12
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?
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A)nonexistent
B)reversed
C)normal
D)half-reversed
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