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Transcript of Sea-Floor Spreading
What is the process of
What is the evidence for
What happens at deep-ocean
The East Pacific Rise is just one of many mid-ocean ridges that wind beneath Earth's ocean.Sonar is a device that bounces sound waves off underwater objects and the records the echoes of these sound waves.The time it takes for the echo to arrive indicates the distance to the object.
What is Sea-Floor Spreading?
Sea-floor spreading continually adds new material to the ocean floor. Sea floor spreads apart along both sides of a mid-ocean ridge as a new crust is added. Ocean floor move by carrying the continents along with them.
Evidence for Sea-Floor Spreading
Several types of evidence supported Hess's theory of sea floor spreading.erupts of molten material, magnetic stripes in the rock of the ocean sea floor,and the ages of the rocks themselves.
Evidence from molten material
such as rocks from only when molten material hardens quickly after erupting under water.These rocks showed that molten rock material has erupted again and again along the mid-ocean ridge.
Evidence from magnetic stripes
Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized ''stripes.'' Stripes hold a record of reversals in Earth's magnetic field. The rock contains iron. The iron is lined up in the direction of Earth's magnetic poles.
Evidence from drilling samples
Scientists determined the age of the samples.
they found that the farther away from a ridge
samples were taken,the older the rocks were.
The youngest rocks were always in the center
of the ridges.This showed that sea-floor spreading
really has taken place.
Subduction at trenches
The ocean floor plunges into deep underwater
canyons called deep-ocean trenches.At a deep-ocean trench, the oceanic crust bends downwards.In a process talking tens of millions of years,part of the ocean floor sinks back into the mantle at deep-ocean trenches.