Lesson 14.3
The Seafloor Spreading
Objectives
At the end
of the
lesson, you
should be
able to:
1
explain how the
seafloor spreads; and
2
describe the structure
and evolution of ocean
basins.
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The Seafloor Spreading
Hypothesis
● Proposed by Harry Hess and
Robert Dietz, this hypothesis
explains the formation of
oceanic crust.
Hess (above) and Dietz
(below)
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Paleomagnetic
Evidence
• Magnetic orientation of the
oceanic crust and the age of
rocks help support that the
ocean floor is spreading.
• The mountain range formed
are drawn towards its
magnetic orientation.
Magnetic orientation patterns
Learn about it!
Paleomagnetic
Evidence
Imprints from rocks show
evidence of magnetic reversals
of Earth.
Normal magnetism will attract
magma outflow towards north
pole while Reverse magnetism
will attract towards the south
pole.
Learn about it!
The Mid-Oceanic Ridge
• Comprises 20% of the
ocean floor’s surface.
• The developed concepts
helped explain the
formation of this ridge.
Mid-oceanic ridge system
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Transform Faults
• These are abundant in
the sea floor.
• Sea floor is divided into
segments as a result.
Transform fault
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Parts of the Ocean Floor
• Abyssal plains are
flat parts of the
ocean.
• Smokers are vents
that spew dark,
mineral-rich fluids.
Ocean floor
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Parts of the Ocean Floor
• Oceanic trenches
depressions on the
seafloor
• A seamount is a
mountain above the
sea floor or “guyot”.
Ocean floor
Learn about it!
Parts of the Ocean Floor
• If the structure rises
above sea level, it is
called a volcanic
island.
• Mid-ocean ridge is a
seafloor mountain
system formed by
plate tectonics.
Ocean floor
Key Points
1
Seafloor spreading hypothesis states the seafloor
moves away from the ridge crest.
2
Paleomagnetism and data from Deep Sea Drilling
Project supported seafloor spreading hypothesis.
3
Mid-oceanic ridge is the longest underwater
mountain range which comprises 20% of Earth’s
surface.