Download Sea- floor Spreading

Sea- floor Spreading
• The longest chain of mountains in the world
is the Mid-Ocean Ridge.
• Scientists have mapped the ocean floor and
mid-ocean ridge using S.O.N.A.R.
• The mid-ocean ridge extends into all of
Earth’s oceans.
• The Island of Iceland is part of the ridge that
rises above the surface in the Atlantic
Ocean.
• Down the middle of the ridge is an area
called the rift valley – It is almost twice as
deep as the Grand Canyon
Harry Hess
• Harry Hess examined maps of the midocean ridge and proposed that the ocean
floors move like conveyor belts, carrying
the continents along with them.
• This movement begins at the Mid- Ocean
Ridge.
• At the ridge, the molten material rises from
the mantle and erupts (much like a
volcano).
• The oldest rock is farthest from the center
of the ridge.
• Harry Hess first proposed the idea of SeaFloor Spreading.
Evidence for Sea-Floor
Spreading:
• 1. Molten Material. Newly hardened
rock on the floor of the ocean
• The submersible ALVIN was sent down
to study the rift valley.
Evidence
2. Rock Sampling. The Glomar Challenger was
a drilling ship the gathered samples from the
ocean floor.
• The scientists determined the age- of the rocks
in the samples and found that the fartheraway from the ridge, the older the rocks were.
• The oldest rocks are about 4 million years old.
• The newer rocks were always in the center of
the ridges
Evidence
3. Magnetic Stripes.
How does the
pattern of matching
stripes show
evidence of seafloor spreading?
As the molten rock cooled the
iron line up in the direction of the Earth’s magnetic
poles. The patterns are the same on both sides
of the mid-ocean ridge
How does the ocean floor keep
getting wider
• The ocean floor plunges
into deep under water
trenches.
• A deep ocean trench forms
where the oceanic crust
collides with continental
crust.
• Subduction is the process by
which the ocean floor sinks
beneath a deep-ocean trench
and back into the mantle.
FYI
• Most ocean trenches are found in the
Pacific Ocean.
• The deepest part of the ocean is the
Marianna’s Deep. It is located in the
Pacific Ocean
• The Pacific Ocean is shrinking, but it is
still the Largest ocean