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Sea-Floor Spreading

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Christine Mallen

on 1 December 2013

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Transcript of Sea-Floor Spreading

Sea-Floor Spreading
Mid-Ocean Ridges
Underwater mountain chains where new ocean floor is created.
As the tectonic plates move away from each other the sea floor spreads apart and magma rises to the surface, cools and solidifies, and becomes new ocean floor.
Sea-Floor Spreading
The process by which new oceanic crust forms as magma rises toward the surface and solidifies.
As this new crust forms, the older crust gets pushed away from the mid-ocean ridge and the sea-floor expands.
Deep-Ocean Trenches
Just as new sea floor is being continuously made, old sea floor is also "disappearing"
at deep underwater canyons known as trenches.
The process in which the crust is pushed down toward the mantle and melts into magma.
The combined efforts of sea-floor spreading and subduction are constantly changing the size and shape of the oceans. This includes renewing the ocean floor about every 200 million years!
Evidence for Sea-Floor Spreading
Molten Rock
Scientists have found igneous rocks on the ocean floor that can only be formed from magma cooling instantly upon contact with water.
Absolute Rock Dating
Samples from the sea floor were brought up and dated. They found that the farther away from the
ridge the samples were taken, the older the rocks were. The youngest rocks were always in the center of the ridges.
Magnetic Reversals
Many times in Earth's history, the north and south magnetic poles have changed places. Alignment of magnetic minerals changes according to the direction of the magnetic poles. Over time this creates "stripes" that show passing time, like the rings of a tree, and we can see the pattern moving away from mid-ocean ridges as new sea-floor is created.
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