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

Sea Floor Spreading Worksheet Analysis and Solutions

The provided worksheet is about the process of sea floor spreading, which is a key concept in plate tectonics. Let's solve each question step by step, referring to the diagram and our understanding of the process.

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#### 1) What feature of the ocean floor is shown at A?

- Answer: The feature at point A is the mid-ocean ridge.
- Explanation: The mid-ocean ridge is a mountainous underwater range where new oceanic crust is formed as molten material rises from the mantle. This is the site of divergent plate boundaries, where two tectonic plates move away from each other.

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#### 2) Describe the process shown occurring at B and explain what results from this.

- Answer: At point B, the process shown is volcanic activity or igneous intrusion. Molten material (magma) rises from the mantle through cracks in the oceanic crust at the mid-ocean ridge. As it reaches the surface, it cools and solidifies, forming new oceanic crust.
- Result: This continuous addition of new crust causes the ocean floor to spread outward from the mid-ocean ridge, pushing older crust away on either side.

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#### 3) What happens to old oceanic crust as new molten material rises from the mantle?

- Answer: As new molten material rises and forms new oceanic crust at the mid-ocean ridge, the older crust is pushed laterally away from the ridge. Eventually, the old oceanic crust moves toward a subduction zone (like the one shown at C) where it sinks back into the mantle due to its greater density compared to the surrounding mantle material.

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#### 4) The arrows on the figure show the ocean floor is spreading from the ridge. What are the two kinds of evidence that scientists found to support this idea?

- Answer:
1. Magnetic striping: Scientists discovered alternating bands of normal and reversed magnetic polarity in the rocks of the ocean floor. These patterns match the Earth's historical magnetic reversals and are symmetrical about the mid-ocean ridge, indicating that new crust is being formed and spreading outward.
2. Age of oceanic crust: Rocks near the mid-ocean ridge 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.

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#### 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 a continental plate or another denser oceanic plate. The denser oceanic plate sinks back into the mantle, forming a subduction zone.
- Why it occurs: Due to the higher density of the oceanic crust compared to the continental crust, the oceanic plate is forced beneath the lighter continental plate. This process recycles the oceanic crust back into the mantle.

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#### 6) Where would you expect to find the “newest” rock on the ocean floor?

- Answer: The newest rock on the ocean floor would be found at the mid-ocean ridge (point A).
- Explanation: New oceanic crust is continuously formed at the mid-ocean ridge as molten material rises from the mantle. Therefore, the rocks closest to the ridge are the youngest.

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#### 7) The feature on the ocean floor at C is called a(n) _______.

- Answer: The feature at point C is called a trench.
- Explanation: A trench is a deep depression in the ocean floor that forms at a subduction zone where one tectonic plate is forced beneath another. It is typically located near the edge of a continent or another oceanic plate.

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#### 8) The process that continuously adds new material to the ocean floor is called _______.

- Answer: The process is called sea floor spreading.
- Explanation: Sea floor spreading refers to the continuous formation of new oceanic crust at the mid-ocean ridge, which causes the ocean floor to expand outward.

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#### 9) The process by which the ocean floor sinks into the mantle is called _______.

- Answer: The process is called subduction.
- Explanation: Subduction occurs when the oceanic crust sinks back into the mantle at a subduction zone, typically near a trench or convergent plate boundary.

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#### 10) The chain of mountains that extends into all of Earth’s oceans is the _______.

- Answer: The chain of mountains is called the mid-ocean ridge system.
- Explanation: The mid-ocean ridge is a continuous mountain range that runs through all the world's oceans, forming the longest mountain chain on Earth. It is the site of sea floor spreading and volcanic activity.

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Final Answers:

1. Mid-ocean ridge
2. Volcanic activity/igneous intrusion; results in the formation of new oceanic crust.
3. Old oceanic crust is pushed away and eventually sinks back into the mantle at subduction zones.
4. Magnetic striping and the age of oceanic crust.
5. Subduction; occurs because the oceanic crust is denser and sinks beneath the continental crust.
6. At the mid-ocean ridge (point A).
7. Trench
8. Sea floor spreading
9. Subduction
10. Mid-ocean ridge system

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Final Answer Box:
\[
\boxed{
\text{1. Mid-ocean ridge} \\
\text{2. Volcanic activity/igneous intrusion; results in new crust.} \\
\text{3. Pushed away and sinks into the mantle.} \\
\text{4. Magnetic striping and age of crust.} \\
\text{5. Subduction; due to density.} \\
\text{6. At the mid-ocean ridge (point A).} \\
\text{7. Trench} \\
\text{8. Sea floor spreading} \\
\text{9. Subduction} \\
\text{10. Mid-ocean ridge system}
}
\]