Ocean floor Ocean floor Continent Molten material (on back) Oceanic crust Mantle Continental crust 1. Name and describe the feature of the ocean floor shown at A. 2. Describe the process shown occurring at B, and explain what results from this. 3. What happens to old oceanic crust as new molten material rises from the mantle? 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? 5. What process is shown occurring at C, and why does it occur? Building Vocabulary Fill in the blank to complete each statement. 6. A device that scientists use to map the ocean floor is 7. The feature on the ocean floor at C is called a(n) 8. The process that continually adds new material to the ocean floor is called Sea-floor spreading 9. The process by which the ocean floor sinks into the mantle is called 10. A chain of underwater mountains along which sea-floor spreading occurs is a Mid-ocean ridge
The Correct Answer and Explanation is:
- Name and describe the feature of the ocean floor shown at A.
The feature at A is likely a mid-ocean ridge. A mid-ocean ridge is an underwater mountain range that runs along the ocean floor, formed by tectonic plates moving apart. It is the site where new oceanic crust is created as molten material rises from the mantle and solidifies.
- Describe the process shown occurring at B, and explain what results from this.
At B, the process is sea-floor spreading. Sea-floor spreading occurs at mid-ocean ridges where tectonic plates move apart, allowing magma from the mantle to rise and solidify, forming new oceanic crust. As the plates continue to move apart, new material is added to the ocean floor, pushing older crust away from the ridge. This process is responsible for the widening of the ocean basins over geological time scales.
- What happens to old oceanic crust as new molten material rises from the mantle?
As new molten material rises from the mantle and creates new oceanic crust at mid-ocean ridges, the older oceanic crust is pushed away from the ridge and moves towards subduction zones. There, it sinks into the mantle and is recycled. This process is part of the plate tectonics cycle, where old crust is destroyed and replaced by new crust, ensuring that the Earth’s crust remains dynamic.
- 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?
Three types of evidence for sea-floor spreading are:
- Magnetic striping: The ocean floor shows alternating bands of magnetic polarity that are symmetrical on both sides of mid-ocean ridges, indicating that new crust is being created and periodically reverses its magnetic polarity.
- Age of oceanic crust: The oceanic crust near the mid-ocean ridges is younger than the crust farther away, supporting the idea of spreading and older crust moving outward.
- Paleontological evidence: Fossil evidence from marine organisms found on opposite sides of mid-ocean ridges suggests that the sea floor has moved apart over time.
- What process is shown occurring at C, and why does it occur?
At C, the process is subduction. This occurs when older, denser oceanic crust moves towards a subduction zone, where it is forced downward into the mantle under the influence of gravity. This happens because the oceanic crust becomes denser as it cools and ages, making it more likely to sink back into the mantle. Subduction plays a key role in the recycling of Earth’s crust and helps drive the movement of tectonic plates.
Building Vocabulary
- A device that scientists use to map the ocean floor is sonar.
- The feature on the ocean floor at C is called a(n) subduction zone.
- The process that continually adds new material to the ocean floor is called sea-floor spreading.
- The process by which the ocean floor sinks into the mantle is called subduction.
- A chain of underwater mountains along which sea-floor spreading occurs is a mid-ocean ridge.
This explanation ties together the processes and features associated with ocean floor dynamics and provides a clearer understanding of how Earth’s tectonic processes shape the oceanic crust.
