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Sea-Floor Spreading

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by

Christine Mallen

on 4 October 2016

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Transcript of Sea-Floor Spreading

Sea-Floor Spreading
Mid-Ocean Ridges
Underwater mountain chains where new ocean floor is created.

Sea-Floor Spreading
IS:
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
Old sea floor is disappearing
at deep underwater canyons known as trenches.
Subduction
IS:
When the collision of two plates causes the crust to be pushed down toward the mantle and melt into magma.
The combined efforts of sea-floor spreading and subduction are constantly moving the continents and changing the size and shape of the oceans. This includes renewing the ocean floor about every 200 million years!
Impact
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.
OCCURS AT:
CAUSES:
Continental Drift
For example, sea-floor spreading at the Mid-Atlantic ridge is slowly pushing North America away from Europe.
OCCURS AT:
CAUSES:
The creation of mountain ranges
and volcanic activity.
Label your Diagram
Full transcript