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Sea-Floor Spreading
Who developed the theory of
continental drift?
A) Wegener
B) Einstein
C) Beethoven
D) Alexander Graham Bell
• Tube Worms - live in the Pacific Ocean
about one mile deep near the
hydrothermal vents.
Who is this?
A) Mr. Crabbs
B) Spongebob
C) Plankton
• .
Worms & Crab
1. Describe the mid-ocean ridge.
• It is the
longest chain
of mountains
in the world
(more than
50,000 km)
on the ocean
floor.
Mid-Ocean Ridge
2. What device is used to map the
ocean floor?
• SONAR
(sound,
navigation,
& ranging)
SONAR Simulation
Yes or No
• SONAR stands for Sound, Navigation, and
Ranging
Harry Hess
• An American
geologist who studied
mid-ocean ridges.
• He suggested that the
ocean floors move
like conveyor belts,
carrying the
continents along with
them.
Who’s theorized about seafloor
spreading?
A) Harry Hess
B) Alfred Wegener
3. Explain the process of Sea-Floor
Spreading
• At the mid-ocean ridge,
molten material rises from
the mantle and erupts. It
spreads out, pushing older
rock to both sides of the
ridge.
4. What evidence supports SeaFloor Spreading?
• A. Evidence # 1 Molten Material
• Explanation: Pillow lava
has been found along
the mid-ocean ridge.
Submersible Recovery
• The submersible,
Alvin, found strange
rocks shaped like
pillows or like
toothpaste squeezed
from a tube.
• Such rocks can form
only when molten
material hardens
quickly after erupting
under water.
B. Evidence # 2 Magnetic Reversals
Explanation: Iron-bearing
minerals in the rock of the
ocean floor hold a record of
reversals in Earth’s magnetic
field. The pattern of reversals
is the same on both sides of
the ridge.
Seafloor Spreading Simulation
Magnetic Stripes
C. Evidence # 3 Drilling Samples.
• Explanation: Younger
rocks
were found in the
center of the ridge,
older rocks were found
farther away from
the ridge at
the trenches.
Glomar Challenger
5. What are deep-ocean trenches?
• Trenches are deep under
water canyons that form
where the oceanic crust
bends downwards.
6. Explain the process of
Subduction.
• A process where the old
ocean floor sinks
beneath a deep-ocean
trench and back into the
mantle.
Subduction Simulation
Subduction
7. Why is the Pacific Ocean
shrinking?
• The trench swallows
more oceanic crust than
the mid-ocean ridge can
produce.
8. Why is the Atlantic Ocean
expanding?
• There are only a few
short trenches around
the Atlantic Ocean so the
spreading oceanic crust
has nowhere to go.
Wilson's Cycle Simulation
In conclusion,
A) Hess’ theory supports Wegener’s theory
B) Wegener’s theory supports Hess’ theory
C) Each are independent theories that stand
on their own