Chapter 5 - Section 4 - Sea-Floor Spreading

Question 1

mid-ocean ridge

Answer 1

An undersea mountain chain where new ocean floor is produced; a divergent plate boundary.

Question 2

sonar

Answer 2

A device that determines the distance of an object under water by recording echoes of sound waves.

Question 3

sea-floor spreading

Answer 3

The process by which molten material adds new oceanic crust to the ocean floor.

Question 4

deep-ocean trench

Answer 4

A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.

Question 5

subduction

Answer 5

The process when the oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Question 6

What is the process of sea-floor spreading?

Answer 6

The sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added.

The ocean floors move like conveyor belts, carrying the continents along with them.

Question 7

What is the evidence for sea-floor spreading?

Answer 7

Scientists found strange rocks that could only have formed when molten material hardens quickly after erupting under water.

Question 8

What happens at deep-ocean trenches?

Answer 8

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

Question 9

What device is used to map the ocean floor?

Answer 9

sonar

Question 10

What process results in the formation of new oceanic crust?

Answer 10

sea-floor spreading

Question 11

What causes the rock of the ocean floor to have a pattern of magnetic stripes?

Answer 11

the reversals of the Earth’s magnetic poles

Question 12

Why is the Pacific Ocean shrinking?

Answer 12

subduction is happening faster than new crust is being added

Question 13

What scientist helped to discover the process of sea-floor spreading?

Answer 13

Harry Hess

Question 14

Along what feature of the ocean floor does sea-floor spreading begin?

Answer 14

a mid-ocean ridge

Question 15

What are the steps in the process of sea-floor spreading?

Answer 15

1. Sea-floor spreading begins at a mid-ocean ridge, which forms along a crack in the oceanic crust.
2. Along the ridge, molten material rises and erupts.
3. At the same time, older rock moves outward on both sides of the ridge.
4. As the molten material cools, it forms a strip of solid rock in the center of the ridge.
5. When more molten material flows into the crack, it forms a new strip of rock.

Question 16

What three types of evidence provided support for the theory of sea-floor spreading?

Answer 16

1. evidence from molten material
2. evidence from magnetic stripes
3. evidence from drilling samples

Question 17

How do rocks along the central valley of the mid-ocean ridge provide evidence of sea-floor spreading?

Answer 17

the type of rocks found could only have been made my molten material harding quickly after erupting under water.