The Ocean Floor

Which of the following is best answer for how a section of ocean water become less dense?

• temperature decreases; salinity increase

• temperature and salinity remain the same

• temperature decreases; pressure decreases

• temperature increases; salinity decreases

Which of the following statements about the extent of Earth’s global ocean is correct?

• It covers about half as much of Earth’s surface as land covers. 
• It covers about the same amount of Earth’s surface as land covers
• It covers more than twice as much of Earth’s surface as land covers.
• It covers more than three times as much of Earth’s surface as land covers.

How do scientists use sonar to study Earth's oceans?

• to map ocean currents
• to map ocean floor
• to measure water density
• to measure underwater earthquakes 

Which two factors mainly determine the temperature of ocean water?

• latitude and depth
• volcanoes and wind 
• sunspot activity and density
• salinity and nutrient concentration 

A scientist is studying a region of the ocean floor. She discovers a long, deep canyon that runs parallel to the coastline of a nearby continent. What can she infer from this discovery?

• The oceanic plate is sliding past the continental plate.
• The oceanic plate is sliding under the continental plate
• The continental plate is sliding under the oceanic plate.
•  The continental plate is pulling away from the oceanic plate. 

Which pair of features of the ocean floor form as two tectonic plates pull away from each other?

• trench and abyssal plain
• trench and abyssal plain
• trench and mid-ocean ridge
• rift zone and mid-ocean ridge

Which statement correctly describes how temperature varies in the ocean's surface zone?

•  It is cooler in areas that have higher salinity. 
• It is warmer in areas that have lower density
•  It is cooler near the poles than near the equator.
• It is warmer where surface currents move the fastest

Which is the main effect that a high rate of evaporation has in a given region of the ocean?

• decreased salinity
• lower temperature
• increased salinity
• higher temperature

Which is a principle that allows scientists to use sonar to map the ocean floor?

• Sound waves travel more quickly through gases than they do through liquids or solids.
• Sound waves travel more quickly through solids than they do through liquids or gases.
• It takes more time for sound pulses to travel through deep water than through shallow water.
• Sound waves have a higher apparent frequency to an observer who is moving toward the sound's source.

Two oceanic plates are pushing against each other. One plate then begins to slide beneath the other. Which type of feature will form as a result of this movement?

• trench
• rift zone
• abyssal plain
• mid-ocean ridge