Sea-Floor Spreading
Learning Target #11

Vocabulary
(Put in Index of Lab Notebook)
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Mid-Ocean Ridge
Sea-Floor Spreading

Learning Target #11:
Seafloor Spreading
Learning Target #11
I can provide the evidence used to support the theory that seafloor spreading has and continues to occur.

Video Hook: Sea-Floor
Spreading
 https://www.youtube.com/watch?v=oX
YAdzmwQsc

Sea-Floor Spreading
Cornell Notes
Directions:
1.
Read the packet (pg 96-98)
2.
3.
4.
1.
2.
View animation (link on bauhsscience.weebly.com)
Write down & answer these questions in lab notebook:
What is the mid-ocean ridge?
What is sea-floor spreading?
3.
4.
How does sea-floor spreading work? (step-by-step)
How does sea-floor spreading provide evidence of Plate
Tectonics/Continental Drift?
Create diagram of sea-floor spreading

1. What is a Mid-Ocean Ridge?


Mid-ocean ridge -mountain ranges in the middle of the oceans. These are the longest mountains in the world.
This is a location where tectonic plates move apart.

Mapping the Mid-Ocean Ridge https://www.youtube.com/watch?v=sgDM6m0lUGY
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Scientists mapped this ridge using a sonar that bounces sound waves off underwater objects and records the distance to that object
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The longer the sound wave takes to return, the deeper that part of the ocean is.
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The shorter the sound wave takes to return, the shallower that part of the ocean is.

2. What is Sea-Floor
Spreading?
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Sea-floor spreading is a process where new sea-floor crust forms along a mid-ocean ridge, which causes older sea-floor crust to move away from the ridge.
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Occurs continuously
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Causes tectonic plates and continents to move apart.
One of the strongest pieces of evidence for Plate Tectonics

3. How Does Sea-Floor
Spreading Work?
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1.
2.
3.
4.
At the mid-ocean ridge:
Molten/melted rock rises up from the asthenosphere (due to convection).
It oozes out onto both sides of the ridge.
It cools and solidifies to create new oceanic rock crust.
As this happens, older sea-floor rock is pushed further away from both sides of the ridge.

4. How Does Sea-Floor Spreading
Provide Evidence of Plate
Tectonics/Continental Drift?
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
Seafloor spreading explains how continents move.
Continents (which are attached to the lithosphere) move as new seafloor crust is created and spreads out and away from the mid-ocean ridge.

Magnetism Mini-Lesson
 https://www.youtube.com/watch?v=YQ
Cq0xX-SvM

Other Evidence of Plate Tectonics http://www.bbc.co.uk/schools/gcsebitesize/science/21c/earth_un iverse/changing_earthrev4.shtml
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Reason #8
Sea-Floor is spreading
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Evidence #8
When new sea floor is created, it pushes older sea floor aside, causing plates and continents to move

Evidence of Sea-Floor
Spreading: Rock Pillows
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Rocks shaped like pillows or toothpaste squeezed from a tube have ben discovered along the Mid-Ocean ridge.
Such rocks form only when molten material hardens quickly after erupting under water
These rocks show that molten material has erupted again and again.

Evidence for Sea-Floor
Spreading: Magnetic Reversal
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Earth’s magnetic poles have switched, and the evidence for this is in the iron bits of the ocean floor rocks created at the Mid-Ocean
Ridge

How Do Scientists Know that the
Magnetic Field has Reversed?
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Scientists can put a magnet up to a piece of rock from the ocean floor.
If the “North” side of the rock repels the “North” side of the magnet, we know that the magnetic fields were normal.
If the “North” side of the rock attracts the “North” side of the magnet, we know that “North” and “South” were switched at that time period.

Evidence of Sea-Floor
Spreading: Age of Ocean Floor
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Evidence from drilling into the sea floor shows allow scientists to determine the ages of rocks
The closer you get to the mid-ocean ridge the younger the rock.
The farther you get, the older the rock.

Evidence of Sea-Floor Spreading:
Fossils on Ocean Floor
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Youngest creature fossils are found all over the ocean floor (since they are not extinct yet). You can tell for sure which are youngest by looking at the rock closest to the mid-ocean ridge.
Oldest creature fossils are shown farthest away from the Mid-Ocean ridge and eventually disappear the closer you get to the ridge (because they are extinct)

Warm-Up 11-20-14

Work on the questions for one of the Seafloor
Spreading Evidence Performance Tasks, or think any questions you need to ask me about what you are working on.
OR
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If you can’t go any further with questions because you are waiting on Google Earth or
Magnetic Reversal stations, come up with a
Kahoot question (write it on a piece of scrap paper from your table bin).

New Unit: Plate Boundaries and Their Affects

Tectonic Plates
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How does the movement of tectonic plates occur?

Plate movement
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What are the three types of tectonic plate movement?
What effect does the movement of the plates have on the earth?

Divergent Plates

New Ocean Floor

Convergent Plates
Oceanic Crust to Continental Crust

Ring of Fire

Convergent Plates
Oceanic Crust to Oceanic Crust

Folded Mountain Chains

Convergent Plates
Continental Crust to Continental Crust

Creates Volcanoes & Island Chains

Transform Plates

Earthquakes

Hawaiian Islands

Boundaries
 https://www.classzone.com/books/eart h_science/terc/content/visualizations/es
0804/es0804page01.cfm?chapter_no=vi sualization