Download 6. Earth`s Crust Moves

Earth’s Crust Moves
Earth’s surface is not a single piece of rock.
Instead, it is made up of many plates. Plates are
rigid blocks of crust and upper mantle rock. Most
of North America, Greenland, and the western
half of the North Atlantic Ocean are on the North
American Plate. Part of California and most of the
Pacific Ocean make up the Pacific Plate. There are about 20 plates in all. Earth’s
plates fit together like the
pieces of a jigsaw puzzle.
Although these plates
are enormous, they actually
float on the soft, mushy rock
of the mantle. Pressure and
heat within the Earth produce
currents in the soft rock of the
mantle. As the mantle moves, the plates floating on it move, too.
Some of the plates
move up to two inches a
year. That’s about as fast
as a fingernail grows. But
because plates are right
next to each other, the
movement of one plate
affects other plates.
Some plates push together. Some pull apart. Other plates slide past each other. As
plates move around, they cause great changes in Earth’s landforms.
Where plates collide, energy is
released, and new landforms are produced.
On land, mountains rise and volcanoes erupt.
South America’s Andes Mountains are a
result of the Nazca and South American
plates colliding. On the ocean floor, deep trenches form.
As plates pull apart on land, valleys dotted with volcanoes develop. Africa’s
Great Rift Valley was formed by the
African and Arabian plates pulling
apart. The rift, or crack, will one day
result in a complete separation of
part of eastern Africa from the rest
of the continent. Where plates pull
apart under the sea, ridges and
volcanoes form. This spreading forms new sea floor at the ridges.
When plates scrape and slide past each other,
they shake Earth’s surface. Along the San Andreas
fault in California, the Pacific
plate is moving past the
North American plate. The
plates rub and shake as they
grind past each other
causing earthquakes.
√What are Earth’s plates?