Download Sea-Floor Spreading

SEA-FLOOR
SPREADING
Sea-Floor Spreading
Mapping the Mid-Ocean Ridge
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The mid-ocean ridge is
the longest chain of
mountains in the
world.
Scientists mapped the
mid-ocean ridge using
sonar.
Sonar is a device that
bounces sound waves
off underwater objects
and records it.
Sea-Floor Spreading
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At the mid-ocean ridge,
molten material rises
from the mantle and
erupts. The molten
material spreads out,
pushing older rock to
both sides of the ridge.
This process that
continually adds to the
ocean floor is sea floor
spreading.
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Evidence for Sea Floor Spreading
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In the 1960s scientists
found evidence that
new material is
erupting along the
mid-ocean ridge.
The presence of pillow
shaped rocks has
showed that molten
material has erupted
again and again.
Evidence for Sea-Floor Spreading
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Evidence in the
rocks shows that
Earth’s magnetic
poles have
reversed.
The iron bits
lined up in the
opposite
direction and
shows this
evidence.
Evidence of Sea-Floor Spreading
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Evidence from
drilling into the sea
floor shows
evidence of the
ages of rocks
The closer you get
to the mid-ocean
ridge the younger
the rock. The
farther you get, the
older the rock.
Subduction in Deep-Ocean
Trenches
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As the ocean spreads
apart, it also plunges
into deep water
canyons called deepocean trenches.
Subduction is the
process by which the
ocean floor sinks
beneath a deep-ocean
trench and back into
the mantle.
Subduction
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The processes of subduction and sea-floor
spreading can change the size and shape of the
oceans.
Because of this processes, the ocean floor is
renewed about every 200 million years.
Subduction in the Oceans
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The Pacific Ocean is shrinking! This is due to the
fact that a deep-ocean trench is swallowing more
crust than the mid-ocean ridge can produce.
The Atlantic Ocean however, is expanding!