Questions and Answers
What is the process of sea-floor spreading?
In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added.
What is the evidence for sea-floor spreading?
Several types of evidence supported Hess's theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.
What happens at ocean trenches?
Part of the ocean floor sinks back into the mantle at deep-ocean trenches.
What are mid-ocean ridges?
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What is sonar?
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What device is used to map the ocean floor?
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What is sea-floor spreading?
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How does new oceanic crust form?
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What happens to the rock along the ridge when new molten material erupts?
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____________________ in the rock of the ocean floor show the direction of Earth's magnetic field at the time the rock hardened.
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How can the ocean floor keep getting wider and wider?
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What occurs at trenches?
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What is a deep-ocean trench?
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What is subduction?
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What happens as subduction occurs?
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How do subduction and Earth's oceans interact?
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Along what feature of the ocean floor does sea-floor spreading begin?
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What three types of evidence provided support for the theory of sea-floor spreading?
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Where would you expect to find the oldest rock on the ocean floor?
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What happens to oceanic crust at a deep-ocean trench?
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Study Notes
Sea-Floor Spreading
- Sea-floor spreading occurs along mid-ocean ridges, where new oceanic crust is formed as molten material erupts, pushing older crust outward.
- The process acts like a conveyor belt, gradually shifting continents.
Evidence for Sea-Floor Spreading
- Key evidence includes:
- Eruptions of molten material.
- Magnetic stripes in ocean floor rocks, revealing Earth's magnetic field direction at solidification.
- Age of rocks, showing a correlation with distance from mid-ocean ridges.
Ocean Trenches
- Deep-ocean trenches are significant geological features where ocean floor is recycled by sinking back into the mantle over millions of years.
- These trenches represent convergent plate boundaries.
Mid-Ocean Ridges
- Mid-ocean ridges are undersea mountain chains where new ocean floor is generated, essential for the process of sea-floor spreading.
Sonar Technology
- Sonar is utilized to map the ocean floor by emitting sound waves and measuring the time for echoes to return, allowing for the determination of underwater features and distances.
Formation of Oceanic Crust
- New oceanic crust is formed through molten material that erupts at mid-ocean ridges and cools, a pivotal aspect of sea-floor spreading.
Movement of Rocks
- As new molten material erupts at mid-ocean ridges, older rocks are displaced outward, illustrating the process of continual crust renewal and ocean floor expansion.
Magnetic Stripes
- Magnetic stripes in oceanic rocks indicate past magnetic orientations, providing insights into tectonic movements over geological time.
Width of the Ocean Floor
- The ocean floor does not infinitely expand; it concurrently sinks into deep-ocean trenches, ensuring a balance between spreading and subduction.
Subduction
- Subduction involves oceanic crust descending beneath deep-ocean trenches and contributes to geological changes over millions of years, effectively cycling oceanic crust.
Interaction of Processes
- Sea-floor spreading and subduction function as interconnected processes, together facilitating the movement of ocean floors like a conveyor belt.
Ocean Floor Renewal
- The ocean floor experiences renewal approximately every 200 million years, transforming its size and shape due to subduction and sea-floor spreading activities.
Oldest Ocean Floor Rocks
- The oldest ocean floor rocks are typically found closer to deep-ocean trenches, indicating their longer exposure and history compared to newer rocks formed at mid-ocean ridges.
Deep-Ocean Trench Characteristics
- Deep-ocean trenches are characterized as deep valleys on the ocean floor where oceanic crust makes a gradual descent towards the mantle, playing a key role in tectonic activity.
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Description
Explore the fascinating process of sea-floor spreading and its significance in plate tectonics. This quiz covers the formation of new oceanic crust, deep-ocean trenches, and the evidence supporting this geological phenomenon. Test your knowledge on mid-ocean ridges and sonar technology.