Sea floor spreading2

1. Sea-Floor Spreading

2. Introduction
•Tube Worms - live in
the Pacific Ocean
about one mile deep
near the hydrothermal
vents.

3. Mapping the mid-ocean ridge
•The East Pacific Rise
has a mid-ocean
ridge.
•Curves around like a
baseball.
•Lies hidden under
hundreds of meters of
water.

4. Sonar
•A device that bounces
sound waves off
underwater objects
and then records the
echoes of these
sound waves.
•Sonar mapped mid-
ocean ridges.

5. 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.

6. •At the mid-ocean ridge, molten material
rises from the mantle and erupts. The
molten material then spreads out, pushing
older rock to both sides of the ridge. As
the molten material cools, it forms a strip
of solid rock in the center of the ridge.
Then more molten material flows into the
crack.

7. Sea-floor spreading
•The process that
continually adds new
material to the ocean
floor.
•Evidence molten
material, magnetic
stripes, and drilling
samples.

8. Evidence #1 - Molten Material
•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.

9. Evidence #2 - Magnetic Stripes
•Scientists discovered
that the rock that
makes up the ocean
floor lies in a pattern
of magnetized
“stripes”. They hold a
record of reversals in
Earth’s magnetic field.

10. Evidence #3 - Drilling Samples
•The Glomar
Challenger did a
drilling sample and
found rocks that the
farther away from the
ridge the older the
rocks were. The
younger ones were in
the center of the
ridge.

11. Subduction at Deep-Ocean
Trenches
•Wider & wider? Deep-
ocean trenches
•Ocean floor plunges into
deep underwater canyons
are deep-ocean trenches.
•Subduction is the process
by which the ocean floor
sinks beneath a deep-
ocean trench and back
into the mantle.

12. Subduction
•At deep-ocean trenches, subduction
allows part of the ocean floor to sink back
into mantle, over tens of millions of years.
•Subduction and Earth’s Oceans
•Earth’s ocean floor is renewed about
every 200 million years.

13. Subduction in the Pacific &
Atlantic
•Deep ocean trenches are swallowing more
oceanic crust than the mid-ocean ridge
can produce. Thus, the width of the
Pacific will shrink.
•The Atlantic is expanding. It has short
trenches. In some places, the oceanic
crust is attached to the continental crust
which moves the continents.