DYNAMIC PLANET33Divergent boundaries At the points where
the mantle currents rise upward, the plates
above them get pulled apart (diverge).
Some of the mantle melts to form magma
and fills the gap between the plates. Each
time this happens the plates move apart.
Sometimes the plates simply slide past
each other without any volcanic activity.
These are called transform boundaries.
EARTH’S CRUST
The uppermost surface of
Earth is called the crust.
It has two layers:
a light top layer and a
slightly thinner but
denser bottom layer.
The crust is broken into
pieces that fit together
like a jigsaw puzzle. These
plates float on the mantle.
As the mantle moves,
the plates go with it.Convergent boundaries When two plates
meet (converge), one of the plates is pulled
under the other. If a continental plate meets
an oceanic plate, the denser oceanic plate
gives way. If two oceanic plates meet, the
cooler, older plate is dragged under. Should
two continental plates collide, the rocks on
both sides bend and fold to form mountains.The oceanic plate
is pulled under
the continental plate.Magma rises up
from the mantle.Plates moving in
opposite directions.TAKE A LOOK: PLATE MOVEMENTSThe continents have
not always been in the
positions they are today.
Since Earth’s crust cooled
they have split, collided,
rotated, and reformed.
They are still moving
about 6 in (15 cm) a year. Today, the continents look
like this, but they are still on
the move.EARTH Over time, the plates
beneath began to pull the
continents apart. About 225 million years
ago all the continents were
joined together.Plates slide past
each other at
transform
boundaries.Ridge forms along
divergent boundary.Direction of
continental
plate.Volcanoes form
where the land
is pushed up.Oceanic crust
forms as the
magma cools
and solidifies.The oceanic
plate starts to
melt and rises
to the surface
as magma.Direction of
oceanic plate.Eurasian plateAfrican plateS. American plateN. American plateAustralian
platePacific plateAntarctic platePacific
plateN. America N. America N. America