Seafloor Spreading

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Evidences of Plate Movements
Part 2 – Week 8 – Science 10

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Objectives
- Describe the possible causes of the plate movement (S10ES –Iaj-36.5)
- Enumerate the lines of evidence that support plate movement. (S10ES –Ia-j-36.6)
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Look back! What are the evidences of Continental
Drift Theory based on the Pictures?
• Fossil Evidence
• Geologic Feature Evidence
• Geologic Fit Evidence
• Jigsaw Fit of the Continents
• Paleoclimatic Evidence

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Seafloor Spreading Theory
and it’s supporting Evidences

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During 50’s to 60’s
Technology pave way to the exploration of
the ocean floor
Methods for seafloor Exploration
• Depth Sounding
• Sonar sounding
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During 50’s to 60’s
Seafloor Exploration Discovery
1. Mid-Ocean Ridges
2. Oceanic Rift Valley
3. Areas found in the deeper part of the ocean
usually have earthquakes near the trenches.
4. The oldest seafloor was found to be a lot
younger compared to the oldest rocks found
on the continents.

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Seafloor Spreading
Theory
Pioneered by Harry Hess and Robert Dietz
• Materials found in the mantle are in motion forming
large convection cells
• Slowly rising hot material spread sideways causing
the seafloor above to be pulled apart
• Molten rock from the mantle will fill these gaps
thereby forming new seafloor while building up the
ridges.
• Over time, the rocks forming the seafloor becomes
cooler and denser. These cause the seafloor to
sink in the area where the downward limbs of the
convection current are located – the trenches
• Based on this fact, it can be concluded that the
seafloor is being recycled.
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Seafloor Spreading Theory
Important in forming new bodies of water.
Red Sea – African and Arabian plate
Atlantic Ocean – North American and Eurasian Plate;
South American and African Plate
The rate of seafloor spreading varies
Seafloor spreading can be calculated by dividing the
distance traveled by the seafloor with the time it takes to
happen.
East Pacific Rise - 6 – 16 centimeters per year
Mid – Atlantic Ridge - 2 – 5 centimeters per year

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Evidences of Seafloor Spreading
Subtitle
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Age of Rocks (Seafloor)
The age of Rocks increases as the
distance to the ridges increases
• 1968 - drilling ship called Glomar
Challenger gather samples of rock in
the ocean.
• Based on this exploration, the scientists
found that the rocks closer to the ridges
are younger.

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Magnetic Reversal
Polarity of the Seafloor is changing together
with the Earth change of Magnetic Field
• There are alternating stripes of normal and
reversed polarity across the ocean.
• These alternating stripes form mirror images on
either side of the mid-ocean ridges.
• The alternating magnetic polarity of rocks ends
at the edge of the continents or the deep-sea
trenches.

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Lets Sum it up
In your own words, discuss briefly our lesson for this day.
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THANK YOU