Oceanography: Sea-Floor Spreading

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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?

An undersea mountain chain where new ocean floor is produced. Signup and view all the answers

What is sonar?

A device that bounces sound waves off underwater objects and then records the echoes. Signup and view all the answers

What device is used to map the ocean floor?

Sonar Signup and view all the answers

What is sea-floor spreading?

The process by which molten material adds new oceanic crust to the ocean floor. Signup and view all the answers

How does new oceanic crust form?

When molten material erupts through the mid-ocean ridge. Signup and view all the answers

What happens to the rock along the ridge when new molten material erupts?

The older rock moves outward on both sides of the ridge as new rock forms in the center. Signup and view all the answers

____________________ in the rock of the ocean floor show the direction of Earth's magnetic field at the time the rock hardened.

Magnetic Stripes Signup and view all the answers

How can the ocean floor keep getting wider and wider?

The ocean floor plunges into deep underwater canyons called deep-ocean trenches. Signup and view all the answers

What occurs at trenches?

Part of the ocean floor sinks back into the mantle at deep-ocean trenches. Signup and view all the answers

What is a deep-ocean trench?

A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle. Signup and view all the answers

What is subduction?

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle. Signup and view all the answers

What happens as subduction occurs?

Crust closer to a mid-ocean ridge moves away from the ridge and toward a deep-ocean trench. Signup and view all the answers

How do subduction and Earth's oceans interact?

The processes of subduction and sea-floor spreading can change the size and shape of the oceans. Signup and view all the answers

Along what feature of the ocean floor does sea-floor spreading begin?

Mid-Ocean ridge Signup and view all the answers

What three types of evidence provided support for the 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. Signup and view all the answers

Where would you expect to find the oldest rock on the ocean floor?

Nearer to deep ocean trenches Signup and view all the answers

What happens to oceanic crust at a deep-ocean trench?

The oceanic crust bends downward and sinks back into the mantle. Signup and view all the answers

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.