Transcript Sea-Floor Spreading

Sea-Floor Spreading
http://www.phschool.com/atschool
/phsciexp/internet_activity/cfd1014_midocean.html
Introduction
• Tube Worms - live in
•
the Pacific Ocean
about one mile deep
near the hydrothermal
vents.
http://www.learningde
mo.com/noaa/
Mapping the mid-ocean ridge
Mid-Ocean Ridge:
underwater
mountain chain.
The Mid-ocean Ridge is
wrapped around the
earth like the curves
around like the
seam on a baseball.
• hidden under
hundreds of meters of
water.
Sonar
• A device that
•
bounces sound
waves off
underwater objects
and then records
the echoes of these
sound waves.
Sonar mapped midocean ridges.
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.
Sea-floor spreading
• The process that
continually adds
new material to the
ocean floor.
• The ocean floors
move like conveyor
belts, carrying the
continents along with
them.
The process of Sea Floor
spreading
• At the mid-ocean ridge:
1: Magma erupts along the mid-ocean
ridge.
2. It then cools to form new ocean
floor.
3. The ocean floor spreads away from
the ridge pushing older rock to both
sides of the ridge.
3 Types of Evidence for Sea Floor
Spreading
• Evidence:
– molten material
– magnetic stripes
– and drilling samples.
Evidence #1 - Molten Material
• The submersible, Alvin,
found strange rocks
shaped like pillows or like
toothpaste squeezed
from a tube. Such
volcanic rocks can form
only when molten
material hardens
quickly after erupting
under water.
Evidence #2 - Magnetic Stripes
• Scientists discovered
that the rock that
makes up the ocean
floor lies in a pattern
of magnetized
“stripes”. They have
a “magnetic
memory” of the
earth.
Evidence #3 - Drilling Samples
• The Glomar
Challenger did a
drilling sample.
• They found that the
father away the crust
was from the ridge,
the older it was. The
youngest ocean
crust is at the ridge
center.
Subduction at Deep-Ocean
Trenches
• Deep Ocean Trenches:
Ocean floor plunges
into deep underwater
canyons
• Subduction: the
process by which the
ocean floor sinks
beneath a deep-ocean
trench and back into
the mantle.
Subduction
• At deep-ocean trenches, subduction
allows part of the ocean floor to sink back
into mantle, over tens of millions of years.
• http://www.learningdemo.com/noaa/
• Earth’s ocean floor is renewed about every
200 million years.
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.