Seafloor Spreading Lesson

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Seafloor Spreading

Process

De La Salle Santiago Zobel School / Junior High School Department,

Science Unit / Term 2, AY 2023-2024 / Earth Science for Grade 7

Subject Teachers: Ms. Lourdes Bual, Mr. Fros Catubigan/ Ms. Rachel Caldaera/

Ms. Jhuly Villanueva

Essential Question:

What mechanisms
drive the seafloor

spreading?

Learning Targets

1. I can describe the initial observations that led to

the formulation of seafloor spreading
hypothesis.

2. I can explain the seafloor spreading process.

3. I can explain how the ocean floor gets recycled.

Recap:
The Continental Drift Theory

Match

Match the following

• Topographic and Tectonic Fit

• Topographic and Tectonic Fit

• Paleoclimatic Evidence

• Paleoclimatic Evidence

• Fossil Correlation

Matching Coastlines

Similarity of Rocks

Coal Deposits in Antarctica

Glacial Striations in Africa

Glossopteris Plant

• Matching Coastlines

• Similarity of Rocks

• Coal Deposits in Antarctica

• Glacial Striations in Africa

• Glossopteris Plant

If we remove
water from the
ocean, how do
you think will the
seafloor look
like?

Draw

If we remove water from the ocean, what do you think will the seafloor look like?

Extensive mapping of
the seafloor
occurred during WWII
because submarines
needed accurate
data for safe
navigation. These
studies continued
after the war, and
led to the discovery
of ocean ridges and
ocean trenches.

The Mid-Ocean ridge is a belt
of underwater mountains
(oceanic-ridges) that
encircles the globe.

The oceanic ridges are made
up of volcanic rocks that give
off an unusual high amount of
heat.

Initial Observations: The Mid-Ocean Ridge

Rift Valley - a lowland central
valley and region that
appears as a “spreading
center” found at the
mid-ocean ridge.

Initial Observations: The Mid-Ocean Ridge

Initial Observations: Frequent Earthquakes near Trenches

Frequent earthquakes
in deep-sea areas
happen and are
detected near trenches.

American geologist Harry Hess (1906–1969) explained the lack of old oceanic crust in 1962. Hess’ theory of seafloor spreading states that hot magma from Earth’s mantle rises up through the mid-oceanic ridges.

Harry Hess and His Hypothesis

1. What do you think
causes the seafloor to
spread?

2. How does the seafloor spreading affect the continents and ocean?

The Sea Floor Spreading Process

Open Ended

1. 1. What do you think
   causes the seafloor to
   spread?

Open Ended

2. How does the seafloor spreading affect the continents and ocean?

1. The hot magma at the ridge erupts
as lava that forms new seafloor.
When the lava cools, the magnetite
crystals take on the current magnetic
polarity. As more lava erupts, it
pushes the seafloor horizontally
away from ridge axis.

The Sea Floor Spreading Process

2. As oceanic crust forms and spreads, moving away from the ridge
crest, it pushes the continent away from the ridge axis.

The Sea Floor Spreading Process

3. If the oceanic crust reaches a deep sea trench, it sinks into the trench and
is lost into the mantle.

The Sea Floor Spreading Process

4. The oldest crust is coldest and lies deepest in the ocean
because it is denser than the hot new crust.

The Sea Floor Spreading Process

Seafloor spreading is the mechanism
for Wegener’s drifting continents.
Convection currents within the mantle
take the continents on a
conveyor-belt ride of oceanic crust
that over millions of years takes them
around the planet’s surface.

The Sea Floor Spreading Process

Linking the Trench and the Mid-Ocean Ridge

Mid-ocean

ridge

Molten
material

Deep
ocean
trench

New

seafloor

forming

upwells upward

through convection
currents and erupts

out of the

reaches the

asthenosphere
again and forms

gets pushed toward a
continental crust and
undergoes subduction

along a

Reorder

Reorder the following stages in the seafloor spreading process.

• The hot magma at the ridge erupts

  as lava that forms new seafloor.

  When the lava cools, the magnetite

  crystals take on the current magnetic

  polarity.

• As more lava erupts, it

  pushes the seafloor horizontally

  away from the ridge axis.

• As oceanic crust forms and spreads, moving away from the ridge

  crest, it pushes the continent away from the ridge axis.

• If the oceanic crust reaches a deep sea trench, it sinks into the trench and

  is lost into the mantle.

• The oldest crust is coldest and lies deepest in the ocean because it is denser than the hot new crust.

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Open Ended

Briefly explain how the ocean floor gets recycled.

Open Ended

WRAP-UP:

What mechanisms drive the seafloor spreading?

Incorporate any of the following words in your answer:

-convection currents

- new ocean floor

- deep ocean trench

- molten material

- mid-ocean ridge

- asthenosphere