Section #: 17.2 Seafloor Spreading

Practice Test
  1.What causes the seafloor to spread?  
  a.   rising molten magma  
  b.   drifting continental crust  
  c.   sinking magma  
  d.   earthquakes  
  2.A __________ is a device that can detect changes in the strength of the magnetic field.  
  a.   satellite  
  b.   magnetometer  
  c.   sonar  
  d.   GPS  
  3.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  
  4.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  
  5.What is the study of Earth's magnetic record?  
  a.   paleogeography  
  b.   magnetometer  
  c.   paleontology  
  d.   paleomagnetism  
  6.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  
  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?

  a.   highly unlikely  
  b.   unlikely  
  c.   likely  
  d.   very likely  
  8.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  
  9.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  
  10.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  
  11.Harry Hess' theory of __________ explained how ocean crust is generated and destroyed.  
  a.   continental drift  
  b.   seafloor spreading  
  c.   plate tectonics  
  d.   continental movement  
  12.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  

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