SECTION 17.2 Seafloor Spreading

Question

In the space at the left, write true if the statement is true: if the statement is false, change the italicized word or phrase to make the statement true.

_________1. Sonar uses sound waves to measure water depth. The italicized word is Sonar

___________ 2. Maps made from sonar and magnetometer data led to the discovery of ocean ridges and deep-sea trenches. The italicized words are ocean ridges and deep-sea trenches

___________ 3. Deep-sea trenches are vast, underwater mountain chains. The italicized words are Deep-sea trenches

____________ 4. Rock samples taken near ocean ridges are older than rock samples taken near deep-sea trenches. The italicized word is older

_____________ 5. The thickness of ocean-floor sediments decreases with distance from an ocean ridge. The italicized word is decreases

__________6. The oldest ocean floor rocks are about 3.8 billion years old. The italicized word is billion

____________7. The study of the magnetic record preserved in Earth's rocks is called paleomagnetism. The italicized word is paleomagnetism

____________8. An isochron is a change in Earth's magnetic field. The italicized word is isochron

___________ 9. Earthquake activity and volcanism are common along ocean ridges. The italicized word is ocean ridges

_____________ 10. The magnetic patterns on either side of a deep-sea trench are mirror images of each other. The italicized word is deep - sea trench

_____________11. The theory of continental drift states that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches. The italicized word is continental drift

___________ 12. As new seafloor is carried away from an ocean ridge, it becomes more dense heats up, expands, and becomes less dense than the material beneath it. The italicized word is heats up, expands, and becomes less dense

___________13. The theory of seafloor spreading explains that Earth's continents move because they ride atop ocean crust as it moves away from
ocean ridges. The italicized words is ride atop ocean crust as it moves away from ocean ridges

The statements below describe the steps involved in the process of seafloor spreading. Number these steps in the order in which they occur.

14. Magma fills the gap that is created.
15. Magma hardens to form new ocean crust.
16. Magma is forced upward toward the crust.

Answer 1

Here are the corrections and numbers in the order of the steps of seafloor spreading:

1. True

2. False - The italicized words are ocean ridges and deep-sea trenches.
   Corrected: Maps made from sonar and magnetometer data led to the discovery of ocean ridges and mid-ocean ridges.

3. False - The italicized words are Deep-sea trenches.
   Corrected: Mid-ocean ridges are vast, underwater mountain chains.

4. False - The italicized word is older.
   Corrected: Rock samples taken near ocean ridges are younger than rock samples taken near deep-sea trenches.

5. False - The italicized word is decreases.
   Corrected: The thickness of ocean-floor sediments increases with distance from an ocean ridge.

6. True

7. True

8. False - The italicized word is isochron.
   Corrected: An isochron is a line on a map that connects points of equal age.

9. True

10. False - The italicized word is deep-sea trench.
    Corrected: The magnetic patterns on either side of a mid-ocean ridge are mirror images of each other.

11. False - The italicized word is continental drift.
    Corrected: The theory of seafloor spreading states that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches.

12. False - The italicized words are heats up, expands, and becomes less dense.
    Corrected: As new seafloor is carried away from an ocean ridge, it becomes more dense, cools down, contracts, and becomes denser than the material beneath it.

13. False - The italicized words are ride atop ocean crust as it moves away from ocean ridges.
    Corrected: The theory of seafloor spreading explains that Earth's continents move because they are carried on the tectonic plates that move due to seafloor spreading.

For the order of the steps in the process of seafloor spreading:

1. 16. Magma is forced upward toward the crust.
2. 14. Magma fills the gap that is created.
3. 15. Magma hardens to form new ocean crust.