Sea-Floor SpreadingSea-Floor Spreading

Sea-Floor SpreadingSea-Floor SpreadingSea-Floor Spreading –the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge

Sea-Floor SpreadingSea-Floor Spreading

Deep in the ocean the water is near freezing.

There is no light

Life is rare

BUT near cracks in the ocean floor, tube worms exist.

Sea-Floor SpreadingSea-Floor SpreadingSonar - a device that bounces sound waves off under-water objects and then records the echoes of these sound waves. The time it takes for the echo to arrive indicates the distance to the object.

Sea-Floor SpreadingSea-Floor SpreadingMid-Ocean RidgeMid-Ocean Ridge – the longest – the longest

chain of mountains in the world---chain of mountains in the world---these are these are divergentdivergent plate plate boundaries.boundaries.

Sea-Floor SpreadingSea-Floor Spreading

In 1960, Hess made his single most In 1960, Hess made his single most important contribution. In a widely circulated important contribution. In a widely circulated report Hess stated that the Earth's crust report Hess stated that the Earth's crust moved laterally away from long, volcanically moved laterally away from long, volcanically active oceanic ridgesactive oceanic ridges

Sea-Floor SpreadingSea-Floor Spreading

Ocean floor moves like a Ocean floor moves like a conveyorconveyor belt belt carrying continents with it. carrying continents with it.

New New ocean floorocean floor forms along cracks in the forms along cracks in the ocean crust as molten material erupts from the ocean crust as molten material erupts from the mantle spreading out and pushing mantle spreading out and pushing older rocksolder rocks to the sides of the crack. New ocean floor is to the sides of the crack. New ocean floor is continually added by the process of continually added by the process of sea-floorsea-floor spreading. spreading.

Sea-Floor SpreadingSea-Floor SpreadingEvidence from Molten Material – Rocks shaped like pillows - show that molten material has erupted again and again from cracks along the mid-ocean ridge and cooled quickly

Sea-Floor Spreading Sea-Floor Spreading EvidenceEvidence

In 1960, scientists used a submersible In 1960, scientists used a submersible named Alvin, to see the ocean floor.named Alvin, to see the ocean floor.

Sea-Floor Spreading Sea-Floor Spreading EvidenceEvidence

Sea-Floor SpreadingSea-Floor SpreadingEvidence from Magnetic Stripes – Rocks that make up the ocean floor lie in a pattern of magnetized stripes which hold a record of the reversals in Earth’s magnetic field

Sea-Floor SpreadingSea-Floor Spreading

Sea-Floor SpreadingSea-Floor Spreading

Sea-Floor SpreadingSea-Floor SpreadingEvidence from Drilling Samples – Core samples from the ocean floor show that older rocks are found farther from the ridge; youngest rocks are in the center of the ridge

Sea-Floor SpreadingSea-Floor SpreadingSubduction – Process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle; allows part of the ocean floor to sink back into the mantle

Sea-Floor Spreading: Sea-Floor Spreading: Subduction zoneSubduction zone

Deep-Ocean Trench – Occurs at subduction zones. Deep underwater canyons form where oceanic crust bends downward

Sea-Floor Spreading: Sea-Floor Spreading: Subduction zone - PacificSubduction zone - Pacific Subduction in the Pacific OceanSubduction in the Pacific Ocean

It is shrinking…how can this be?It is shrinking…how can this be? A deep ocean trench swallows more oceanic A deep ocean trench swallows more oceanic

crustcrust No new crust is being addedNo new crust is being added

Sea-Floor Spreading: Sea-Floor Spreading: Subduction zone - Subduction zone -

AtlanticAtlantic Is expandingIs expanding Only a few short trenchesOnly a few short trenches As a result, the spreading ocean floor As a result, the spreading ocean floor

has nowhere to gohas nowhere to go So…as long as the Atlantic Ocean So…as long as the Atlantic Ocean

spreads so does the continents along its spreads so does the continents along its bordersborders

Sea-Floor SpreadingSea-Floor Spreading