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Transcript of Seafloor Spreading
Lithosphere: Continental vs. Ocean Crust
The Sea Floor Moves
The Seafloor Moves
Mapping the Ocean Floor using Sonar.
is a device that bounces sound waves off under water objects and then records the echoes of these sound waves.
How did we figure this out?
(crust + upper mantle) sits higher on the plastic-like
and is made of
(made of basalt) covers the ocean floor
The ocean floor is covered with underwater mountain chains called the
, the longest chain of mountains in the world.
What is happening at the
The seafloor is
spreading apart at
the mid-ocean ridge.
As molten material (magma) rises from the mantle at the mid-ocean ridge, the magma/lava cools forming
is pushed away like a conveyor belt.
, an American geologist, was one of the scientists to study the mid-ocean ridge.
Hess said that at the mid-ocean ridge, molten material inside Earth's crust called
, rises from the mantle and erupts. The hot material after it emerges onto Earth's surface called
, then spreads out, pushing older rock to both sides of the ridge. He called this process that continually adds new material to the ocean floor
How can the ocean floor keep getting wider?
The ocean floor doesn't just keep spreading. The oceanic crust/plate is
. It plunges into deep water canyons called
deep ocean trenches.
The process by which the oceanic crust/plate sinks beneath a deep-ocean trench and back into the mantle where it is recycled.
Subduction in the Pacific Ocean
The Pacific Ocean is shrinking. It has many deep-ocean trenches that are swallowing more oceanic crust than the mid-ocean ridge can produce.
Subduction in the Atlantic Ocean
It is expanding because there are fewer trenches, therefore less subduction is taking place.
EVIDENCE FOR SEA FLOOR SPREADING
Evidence from molten material
Rocks shaped like pillows show that
molten material has erupted again and again from cracks at the mid-ocean ridge and cooled.
2. Evidence from magnetic stripes
Rocks that make up ocean floor
lie in a pattern of magnetic stripes
where one stripe shows Earth's
magnetic field pointing north and
the next parallel stripe points south.
3. Evidence from drilling samples
Samples from ocean floor show
that older rocks are found farther from the mid-ocean ridge; younger rocks are closer to the center of the ridge.
(made of granite) forms the land and continents on Earth.
What would we see if we drained off all the water on Earth surface?