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In sea-floor spreading, new crust is added at a ___.

mid-ocean ridge

Subduction takes place at ____.

deep-ocean trenches

What happens to old oceanic crust as new molten material rises from the mantle?

the new material splits apart the old material and pushes it outward from the ridge

A canyon on the ocean floor at which the crust bends downward is called a ___.

deep-ocean trench

The process that continually adds new material to the ocean floor is called ___.

Sea floor spreading

THe process by which the ocean floor sinks into the mantle is known as ___.


A chain of underwater mountains along which sea-floor spreading occurs is a ___.

mid-ocean ridge

Which processes change the size and shape of the oceans?

sea floor spreading and subduction

Where does subduction occur?

at deep ocean trenches

Where does sea floor spreading occur?

down the middle of underwater mountain ranges

____ is a device that scientist use to map the ocean floor


A deep-ocean trench is an underwater ___.


Molten material erups ____ the central valley of mid-ocean ridges.


The farther from a mid-ocean ridge a rock sample is taken the ____ the rock is.


The pattern of magnetic stripes in rocks on either side of a mid-ocean ridge is the ____.


Suppose Earth's magnetic polarity changed many time over a short period. What pattern of striping at a mid-ocean ridge would you expect to find?

both sides of the ridge would have many narrow stripes

Why does subduction occur?

Gravity causes older, denser oceanic crust to sink beneath less dense continental crust

Oceanic crust near the mid-ocean ridge is ____ than oceanic crust farther away from the ridge


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