Sea Floor Spreading Worksheet diagram depicting the formation of new oceanic crust at a mid-ocean ridge and the movement of tectonic plates.

Sea Floor Spreading Worksheet Solution

#### 1) What feature of the ocean floor is shown at A?
- Answer: Mid-ocean ridge (or divergent boundary)

#### 2) Describe the process shown occurring at B, and explain what results from this.
- Answer: At point B, the process shown is sea floor spreading. This occurs where two tectonic plates are moving apart from each other at a divergent boundary (mid-ocean ridge). As the plates separate, molten material from the mantle rises to fill the gap, solidifying into new oceanic crust. This continuous process leads to the formation of new oceanic crust and the widening of the ocean basin over time.

#### 3) What happens to old oceanic crust as new molten material rises from the mantle?
- Answer: As new molten material rises from the mantle and forms new oceanic crust at the mid-ocean ridge, the older crust is pushed away from the ridge in both directions. Over time, the oldest oceanic crust moves toward the edges of the ocean basin, where it eventually encounters subduction zones (like point C in the figure). Here, the old oceanic crust sinks back into the mantle due to its greater density compared to the surrounding mantle material.

#### 4) The arrows on the figure show the ocean floor spreading from the ridge. What are three kinds of evidence scientists have found to support this idea?
- Answer: Scientists have found the following three types of evidence to support the idea of sea floor spreading:
1. Magnetic striping: The ocean floor has alternating bands of magnetic polarity parallel to the mid-ocean ridges. These patterns match Earth's historical reversals of magnetic polarity, indicating that new crust forms symmetrically on either side of the ridge.
2. Age of oceanic crust: Rocks near the mid-ocean ridges are younger, while those farther away are progressively older. This supports the idea that new crust is continuously forming at the ridge and moving outward.
3. Heat flow measurements: Higher heat flow is observed near the mid-ocean ridges, indicating recent volcanic activity and the upwelling of hot magma from the mantle.

#### 5) What process is shown occurring at C, and why does it occur?
- Answer: At point C, the process shown is subduction. Subduction occurs when an oceanic plate collides with another plate (either oceanic or continental) and is forced to sink back into the mantle due to its greater density. This process typically occurs at convergent boundaries, such as where an oceanic plate meets a continental plate or another denser oceanic plate. Subduction results in the recycling of oceanic crust back into the mantle and is responsible for the destruction of old oceanic crust.

#### 6) Where would you expect to find the oldest rock on the ocean floor?
- Answer: The oldest rock on the ocean floor would be found farthest away from the mid-ocean ridge. This is because new oceanic crust is continuously formed at the mid-ocean ridge, and as it moves away, it becomes progressively older. The oldest oceanic crust is typically found near the edges of the ocean basins, close to subduction zones like point C.

#### 7) A device that scientists use to map the ocean floor is ___________.
- Answer: Sonar (Sound Navigation and Ranging)

#### 8) The feature on the ocean floor at C is called a(n) ___________.
- Answer: Trench

#### 9) The process that continually adds new material to the ocean floor is called ___________.
- Answer: Sea floor spreading

#### 10) The process by which the ocean floor sinks into the mantle is called ___________.
- Answer: Subduction

#### 11) The chain of mountains that extends into all of Earth’s oceans is the ___________.
- Answer: Mid-ocean ridge system

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Final Answers:

1. Mid-ocean ridge (or divergent boundary)
2. Sea floor spreading; new crust forms as plates move apart, widening the ocean basin.
3. Old oceanic crust is pushed away from the ridge and eventually sinks into subduction zones.
4. Magnetic striping, age of oceanic crust, heat flow measurements.
5. Subduction; occurs due to the denser oceanic plate sinking into the mantle.
6. Farthest away from the mid-ocean ridge, near subduction zones.
7. Sonar
8. Trench
9. Sea floor spreading
10. Subduction
11. Mid-ocean ridge system

Final Answer: \boxed{1. Mid-ocean ridge, 2. Sea floor spreading, 3. Pushed away and sinks, 4. Magnetic striping, age of crust, heat flow, 5. Subduction, 6. Farthest from ridge, 7. Sonar, 8. Trench, 9. Sea floor spreading, 10. Subduction, 11. Mid-ocean ridge system}