FQ: How could continents move FQ: How could continents move apart?apart?

1. Think, pair, share1. Think, pair, share

2. Write your ideas in your scientist 2. Write your ideas in your scientist notebooknotebook

Mapping the Ocean FloorMapping the Ocean Floor

SonarSonar was used in the mid 1900’s to was used in the mid 1900’s to map the ocean floormap the ocean floor

Sonar bounces sound waves off Sonar bounces sound waves off objects and records the echoes of objects and records the echoes of these waves.these waves.

Time it takes for echo to come back Time it takes for echo to come back indicates the distance from the indicates the distance from the objectobject

Sonar discovered the Sonar discovered the mid-ocean mid-ocean ridgesridges

Sonar Animation

Mid-Ocean RidgesMid-Ocean RidgesThe Mid-ocean Ridge The Mid-ocean Ridge is a chain of is a chain of underwater mountains that extend into underwater mountains that extend into all of Earth’s oceans. all of Earth’s oceans. They are more than 50,000 km longThey are more than 50,000 km longMost are under hundreds of meters of Most are under hundreds of meters of waterwaterThey reach the surface in a few places They reach the surface in a few places such as Iceland.such as Iceland.Rift Valley Rift Valley - A steep sided valley splits - A steep sided valley splits the top of some mid-ocean ridges.the top of some mid-ocean ridges.

Iceland Rift ValleyIceland Rift Valley

MID-OCEAN RIDGES

Mid- Ocean RidgesMid- Ocean Ridges

Sea Floor SpreadingSea Floor Spreading

In 1960 In 1960 Harry HessHarry Hess, an American , an American geologist, suggested that the sea floor geologist, suggested that the sea floor spread apart along both sides of a mid-spread apart along both sides of a mid-ocean ridge as new crust is added.ocean ridge as new crust is added.

As a result the ocean floors move like As a result the ocean floors move like conveyor belts carrying continents with conveyor belts carrying continents with them.them.

He called this He called this sea-floor spreadingsea-floor spreading

Molten material erupts through the rift Molten material erupts through the rift valley in the center of the ridge. Hardens valley in the center of the ridge. Hardens and cools to form new sea floor.and cools to form new sea floor.

Sea Floor SpreadingSea Floor SpreadingAnimation

Evidence for sea floor spreadingEvidence for sea floor spreading

From Molten MaterialFrom Molten Material– Alvin, The world’s first deep ocean Alvin, The world’s first deep ocean

submersible used for deep sea submersible used for deep sea exploration, found strange rocks shaped exploration, found strange rocks shaped like pillows in the mid-ocean ridge. This like pillows in the mid-ocean ridge. This was evidence was evidence

that molten materialthat molten material

came out of thecame out of the

ridge andridge and

hardened quicklyhardened quickly

Bulbous Pillow LavaBulbous Pillow Lava

Evidence from Magnetic Evidence from Magnetic StripesStripes

Scientists studied the rock patterns in the ocean Scientists studied the rock patterns in the ocean floor .floor .

They found that the rock on the ocean floor lies in They found that the rock on the ocean floor lies in a pattern of magnetized stripesa pattern of magnetized stripes

Magnetic stripes Magnetic stripes in ocean floor rocks are formed in ocean floor rocks are formed by the reversal of the Earth’s magnetic poles. by the reversal of the Earth’s magnetic poles.

The last reversal happened 780,000 years ago.The last reversal happened 780,000 years ago.

The pattern of stripes matches on each side of The pattern of stripes matches on each side of the ocean ridge.the ocean ridge.

Magnetic stripesMagnetic stripesAnimationAnimation

Evidence from drilling samplesEvidence from drilling samples

Glomar Challenger gathered samples of Glomar Challenger gathered samples of rocks by drilling into the ocean floorrocks by drilling into the ocean floor

Drilled through 6 km of water into ocean Drilled through 6 km of water into ocean floorfloor

Scientists then determined the age of the Scientists then determined the age of the rocksrocks

They found that the rocks next to ocean They found that the rocks next to ocean ridges are younger than rocks farther ridges are younger than rocks farther away.away.

As the ocean floor spreads the older rocks As the ocean floor spreads the older rocks move farther away.move farther away.

Age of Ocean RocksAge of Ocean Rocks

Is the Earth’s surface Is the Earth’s surface getting larger from sea-floor getting larger from sea-floor

spreading?spreading?

Subduction at TrenchesSubduction at Trenches

Deep ocean trenches Deep ocean trenches are deep underwater are deep underwater canyons canyons

In a process that takes tens of millions of In a process that takes tens of millions of years, the ocean floor sinks back into the years, the ocean floor sinks back into the mantle at deep ocean trenches.mantle at deep ocean trenches.

SubductionSubduction is the process where the ocean is the process where the ocean floor sinks beneath a deep ocean trench.floor sinks beneath a deep ocean trench.

Subduction animationSubduction animation

Subduction zonesSubduction zones

Oceanic crust and Continental crust Oceanic and Oceanic

Crust

Seafloor Spreading and Seafloor Spreading and Subduction (animation)Subduction (animation)

Sea-floor spreading and subduction Sea-floor spreading and subduction work together like a conveyor belt.work together like a conveyor belt.

New oceanic crust is hot.New oceanic crust is hot.

As it moves away from the ridge it As it moves away from the ridge it cools, and becomes more densecools, and becomes more dense

At a trench, the older, more dense At a trench, the older, more dense crust is pulled by gravity and sinks crust is pulled by gravity and sinks down beneath the trenchdown beneath the trench

Sea floor spreading and Sea floor spreading and subduction (animation)subduction (animation)

Subduction and the Earth’s Subduction and the Earth’s OceansOceans

Sea-Floor spreading and subduction can Sea-Floor spreading and subduction can change the size and shape of the oceans.change the size and shape of the oceans.

Ocean floor is renewed every 200 million Ocean floor is renewed every 200 million years – the time it takes for the floor to years – the time it takes for the floor to travel from ridge to trench.travel from ridge to trench.

The Pacific Ocean The Pacific Ocean is shrinking. More crust is shrinking. More crust is being subducted than is being formed.is being subducted than is being formed.

The Atlantic Ocean The Atlantic Ocean is expanding. More is expanding. More crust is being formed than is being crust is being formed than is being subducted.subducted.

ReferencesReferences

http://www.whoi.edu/page.do?pid=8422http://www.whoi.edu/page.do?pid=8422

http://ocean-ridge.ldeo.columbia.edu/http://ocean-ridge.ldeo.columbia.edu/courses/subgeol/courses/subgeol/mid_ocean_landscape.htmlmid_ocean_landscape.html

http://oceansjsu.com/105/http://oceansjsu.com/105/exped_commotion/8.htmlexped_commotion/8.html