SEA-FLOOR SEA-FLOOR SPREADINGSPREADING

Sea-Floor SpreadingSea-Floor Spreading

Mapping the Mid-Ocean RidgeMapping the Mid-Ocean Ridge

The mid-ocean ridge The mid-ocean ridge is the longest chain is the longest chain of mountains in the of mountains in the world.world.

Scientists mapped Scientists mapped the mid-ocean ridge the mid-ocean ridge using sonar.using sonar.

Sonar is a device that Sonar is a device that bounces sound bounces sound waves off underwater waves off underwater objects and records objects and records it.it.

Sea-Floor SpreadingSea-Floor Spreading At the mid-ocean At the mid-ocean

ridge, molten material ridge, molten material rises from the mantle rises from the mantle and erupts. The and erupts. The molten material molten material spreads out, pushing spreads out, pushing older rock to both older rock to both sides of the ridge.sides of the ridge.

This process that This process that continually adds to continually adds to the ocean floor is sea the ocean floor is sea floor spreading.floor spreading.

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Evidence for Sea Floor Evidence for Sea Floor SpreadingSpreading

In the 1960s In the 1960s scientists found scientists found evidence that new evidence that new material is erupting material is erupting along the mid-ocean along the mid-ocean ridge.ridge.

The presence of The presence of pillow shaped rocks pillow shaped rocks has showed that has showed that molten material has molten material has erupted again and erupted again and again.again.

Evidence for Sea-Floor Evidence for Sea-Floor SpreadingSpreading

Evidence in the Evidence in the rocks shows rocks shows that Earth’s that Earth’s magnetic poles magnetic poles have reversed.have reversed.

The iron bits The iron bits lined up in the lined up in the opposite opposite direction and direction and shows this shows this evidence.evidence.

Evidence of Sea-Floor Evidence of Sea-Floor SpreadingSpreading

Evidence from Evidence from drilling into the drilling into the sea floor shows sea floor shows evidence of the evidence of the ages of rocksages of rocks

The closer you The closer you get to the mid-get to the mid-ocean ridge the ocean ridge the younger the younger the rock. The farther rock. The farther you get, the you get, the older the rock.older the rock.

Subduction in Deep-Ocean Subduction in Deep-Ocean TrenchesTrenches

As the ocean spreads As the ocean spreads apart, it also plunges apart, it also plunges into deep water into deep water canyons called deep-canyons called deep-ocean trenches.ocean trenches.

Subduction is the Subduction is the process by which the process by which the ocean floor sinks ocean floor sinks beneath a deep-beneath a deep-ocean trench and ocean trench and back into the mantle.back into the mantle.

SubductionSubduction The processes of subduction and sea-floor The processes of subduction and sea-floor

spreading can change the size and shape of the spreading can change the size and shape of the oceans.oceans.

Because of this processes, the ocean floor is Because of this processes, the ocean floor is renewed about every 200 million years.renewed about every 200 million years.

Subduction in the OceansSubduction in the Oceans The Pacific Ocean is shrinking! This is due to the The Pacific Ocean is shrinking! This is due to the

fact that a deep-ocean trench is swallowing more fact that a deep-ocean trench is swallowing more crust than the mid-ocean ridge can produce.crust than the mid-ocean ridge can produce.

The Atlantic Ocean however, is expanding!The Atlantic Ocean however, is expanding!