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 sinks back into the mantle at subduction zones 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: Three kinds of evidence supporting sea floor spreading include:
1. Magnetic striping patterns: The ocean floor has alternating bands of normal and reversed magnetic polarity, which match the Earth's past magnetic reversals. These patterns are symmetrical about the mid-ocean ridge, indicating that new crust forms there and spreads outward.
2. Age of oceanic crust: Rocks near the mid-ocean ridge are younger, while those farther away are progressively older, consistent with the idea that new crust forms at the ridge and spreads outward.
3. Heat flow measurements: Higher heat flow is observed near the mid-ocean ridge, indicating recent volcanic activity and magma upwelling, which supports the idea of sea floor spreading.

#### 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 oceanic plate. Subduction results in the recycling of oceanic crust back into the mantle and can lead to the formation of deep ocean trenches, volcanic arcs, and earthquakes.

#### 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 from the mid-ocean ridge. This is because new oceanic crust is continuously formed at the mid-ocean ridge and spreads outward, with the oldest crust being pushed toward the edges of the ocean basin, where it eventually subducts.

#### 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 back into the mantle at subduction zones.
4. Magnetic striping patterns, age of oceanic crust, and heat flow measurements.
5. Subduction; occurs due to the denser oceanic plate sinking beneath another plate.
6. Farthest from the mid-ocean ridge.
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 subducted, 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}