Seafloor Spreading
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Come in Silently, take out your weekly
organizer, and work on your Do Now
SILENTLY and INDEPENDENTLY:
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1. List and Define the Three types of Heat
Transfer
2. Describe Convection Currents
3. Describe Density
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What is the process of sea-floor spreading?
What is the evidence for sea-floor spreading?
What happens at deep-ocean trenches?
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http://oceantoday.noaa.gov/deepocean/
Temperatures are near
freezing
 There is no light or living
things
 Some areas of the deepocean floor has a lot of life
 The East Pacific Rise - This
area is near the costs of
Mexico and South America
 Here, ocean water sinks
through the cracks and is
heated by which layer?
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Around these areas live
bizarre creatures
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Mid-ocean Ridge – undersea
mountain chain that is part of a
long system of mountains
beneath the Earth’s Oceans
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Scientists made a map using
Sonar.
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Sonar – device that bounces
sound waves off underwater
objects and records the echoes
of these sound waves
The ridges lie hidden under
the water
 Some places, the ridge
pokes above the surface
 Iceland is part of the midocean ridge
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How did these ridges form?
One geologist proposed the
idea of Sea-floor spreading
The sea floor spreads apart
along both sides of a midocean ridge as new crust is
added. As a result, the
ocean floors move like
conveyor belts, carrying the
continents along with them
Forms along a crack in the oceanic crust
Motel material rises and erupts
The older rock moves outward on both sides of the
ridge
 As the molten material cools it forms a strip of rock in
the middle
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Several types of evidence supported the theory of sea-floor
spreading: eruptions of molten material, magnetic stripes
in the rock of the ocean floor, and the ages of the rocks
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Scientists dived to the ocean floor in a small submarine.
The submarine found strange rocks shaped like pillows
Other rocks looked like toothpaste
These rocks form only when molten material hardens quickly
under rock
Earth’s magnetic poles have reversed many times in its
history
 Scientists discovered that the rocks lie in a pattern of
magnetized “stripes”
 The stripes show the Earth’s reversal in its magnetic field.
 Iron is found in the rocks and as it cooled, the iron lined up to
the direction of Earth’s Magnetic poles
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Rock samples obtained by drilling into the ocean floor
Scientists determined the age of rocks in the samples
Found that the farther away from a ridge, the older the rocks
were
 The youngest rocks were always in the center of the ridge
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