Sea-Floor Spreading - Science

Divergent Boundaries ?

Pull Apart.

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?

- Molten Material (Magma/Lava) - Magnetic Stripes - Drilling Samples

What is the mid-ocean ridge?

A chain of mountains that runs along the middle of the ocean floor. The mid-ocean ridge forms along a crack in the oceanic crust.

What happens to the ocean floor at deep-ocean trenches?

At deep-ocean trenches, subduction allows part of the ocean floor to sink back into the mantle, over tens of millions of years.

What is the process of sea-floor spreading?

At the mid-ocean ridge, molten material rises from the asthenosphere/mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge. As the molten material cools, it forms a strip of solid rock in the center of the ridge. Then more molten material splits apart the strip of solid rock that formed before, pushing it aside. This process, called sea - floor spreading, continually adds new material to the ocean floor.

What is the longest chain of mountains in the world?

Mid-ocean ridge

The chain of mountains that extends into all of Earth's oceans is the?

Mid-ocean ridge.

How does Earth's ocean floors move?

Move like Conveyor belts, carrying the continents along with them.

The process that continually adds new material to the ocean floor is called?

Sea-floor spreading.

How did scientists map the mid - ocean ridge in the 1900's?

Sonar

A device that scientists use to map the ocean floor?

Sonar.

What is subduction?

Subduction is the process which the ocean floor sinks beneath a deep-ocean trench and back into the mantle. (A process by which part of Earth's crust sinks downwards).

What are deep-ocean trenches?

The ocean floor doesn't just keep spreading. Instead, it sinks beneath deep underwater canyons called deep-ocean trenches.

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

The old crust is pushed away and new crust takes over.

Describe the process shown at point B and explain what results from this.

The process is called sea-floor spreading. Ridges form along cracks (divergent boundaries) in the oceanic crust (Molten rock (magma) rises through these cracks and pushes to both sides. When it cools, it forms new oceanic crust. The old crust is pushed away and new crust takes over. This is called Sea-Floor Spreading. (Sea-floor spreading adds more crust to the ocean floor. At the same time, older strips of rock move outward from either side of the ridge).

What process is shown occurring at point C and why does it occur?

The process is called subduction. Deep-ocean trenches. Where there are trenches, subduction takes place. Subduction is the process where the ocean floor sinks beneath a deep-ocean trench and back into the mantle. At deep-ocean trenches, subduction allows part of the ocean floor to sink back into the mantle, over tens of millions of years.

How does the ridge form?

The ridge forms along a crack in the oceanic crust.

What are 3 kinds of evidence scientists have found to support the theory of sea-floor spreading?

1) Molten Material (magma/lava) - scientists have found strange rocks shaped like pillows in the central valley of the ocean ridge. Such rocks can form only if molten material hardens quickly after erupting under water. The presence of these rocks supports the theory of sea-floor spreading. 2) Magnetic Stripes - The molten rock contains iron - it is magnetic. As it cools, the iron bits inside line up in the direction of the Earth's magnetic poles. Once the rock is hardened completely, it locks the iron bits in place, giving the ocean floor a pattern of magnetic stripes. The pattern is the same on both sides of the ridge. These stripes hold a record of reversals in Earth's magnetic field. 3) Drilling Samples - the Glomar challenger drilled holes in the ocean 6km deep. Samples from the sea floor showed that the further away the rocks were from the ridge, the older it was. The younger rocks were always found at the center of the ridges. At the ridge center, molten material erupts and cools to form new crust. Like the Conveyer Belt.

How does Sonar work?

A device that bounces sound waves off underwater objects and then records the echoes of these sound waves.

What is sonar?

A device that scientists use to map the ocean floor, using sound waves to measure the distance of an object.

Where does Earth's ocean floors' movement begin?

Begins at the mid - ocean ridge.

What impact does the process of subduction and sea-floor spreading have on the ocean floor?

Both processes can change the shape and size of the oceans. Because of these processes, the ocean floor is renewed about every 200 million years. That is the time it takes for new rock to form at the mid-ocean ridge., move across the ocean and sink into a trench. They move the ocean floor as if it were on a giant conveyor belt. The Pacific Ocean is shrinking. Its many deep ocean trenches are swallowing more ocean crust than the mid ocean ridge is producing. The Atlantic Ocean is expanding. This ocean has only a few short trenches. As a result, the spreading ocean floor has almost nowhere to go. In most places, the oceanic crust of the Atlantic Ocean is attached to the continental crust of the continents around the ocean. As the Atlantic's floor spreads, the continents along its edges also move. Over time, the whole ocean gets wider.

Convergent Boundaries?

Come Together.

The feature on the ocean floor at point C is called a?

Deep-ocean trench.

Name and describe the feature of the ocean floor shown at A.

It is called the mid-ocean ridge. This feature causes mountains to form when magma cools. Most of these mountains lie hidden under water. However, there are places where the ridge pokes above the surface. ex: Iceland is part of the mid-ocean ridge.

What is sea-floor spreading?

Process where mid-ocean ridges continually add new material to the ocean floor.

The process by which the ocean floor sinks into the mantel is called?

Subduction.

What structures lie beneath Earth's oceans?

The Earth has valleys and mountains, because of volcanoes that erupt in the ocean.

How are the sizes of Earth's oceans determined?

The sizes of Earth's oceans are determined by how fast new crust is being created at mid-ocean ridges and how fast old crust is being swallowed up at deep-ocean trenches An ocean surrounded by many trenches may shrink. An ocean with few trenches will probably grow larger.

What happens at deep-ocean trenches?

Where there are trenches, part of the ocean floor sinks back into the mantle (subduction takes place).