Page 159 - Science Course 2 (Book 2)

Mo11-L5a: What is Seaf oor Spreading?

Seaf oor Spreading Scientists argued that if the seaf oor spreads, the
continents must also be moving.
By the 1960s, scientists discovered the process of
seaf oor spreading.

Seaf oor spreading is the process by which new
oceanic crust forms along a mid-ocean ridge and
older oceanic crust moves away from the ridge.

When the seaf oor spreads, the mantle below melts
and forms magma.

Key Concept

What is Seaf oor Spreading?
What is seaf oor spreading?

Rising Magma
Upper Mantle Upper Mantle

Magma erupts on Earth’s surface as lava, which
cools and crystallizes on the seaf oor, forming rock.

Because the lava erupts into water, it cools rapidly
and forms rounded structures called pillow lavas.

The rugged mountains that make up the mid-ocean
ridge system can form in two different ways.

Large amounts of lava can erupt from the center of
the ridge, cool, and build up around the ridge.

As the seaf oor continues to spread apart, the older
oceanic crust moves away from the mid-ocean ridge.

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