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Transcript of Sea-Floor Spreading
Underwater mountain chains where new ocean floor is created.
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.
Old sea floor is disappearing
at deep underwater canyons known as trenches.
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!
Evidence for Sea-Floor Spreading
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.
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.
For example, sea-floor spreading at the Mid-Atlantic ridge is slowly pushing North America away from Europe.
The creation of mountain ranges
and volcanic activity.
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