Plate Tectonics - How does the Earth's Crust get its Shape?
crust is very thin compared to
the size of the planet.
It is thinner than an eggshell is compared to the size of an egg.
The Earth's crust is solid and lies on top of the mantle.
The mantle contains both hot solid rock and magma.
Some scientists once believed that
the features of
the Earth's surface (hills, valleys, plains and mountains)
were caused by the Earth shrinking as it cooled down
from its original state. Now scientists believe that the
Earth's features are caused by the movement of tectonic plates.
What are the Tectonic Plates?
The Earth's crust is broken into
six large and many smaller pieces.
These pieces are called plates. The plates are given names according
to the land masses that they carry. For example, there is the
Pacific Plate, Eurasian Plate, African Plate, North American Plate
and so on. You do not need to remember these names.
Why do Tectonic Plates Move?
The plates are always
moving, on convection currents
in the hot mantle. This is called continental drift.
Heat is generated in the mantle by natural processes of
radioactive decay. The plates move very very slowly,
only a few centimeters per year on average.
Where the plates collide or grind past each other,
rocks are stretched, crushed, deformed and sometimes melted.
This is called tectonic activity (see the rock cycle).
The theory of plate tectonics and
suggested by Alfred Wegener in the 1920s but it was not
accepted for many years as the evidence for it was open to question.
At that time there was no known way that continents could move
and Wegner was considered to be an outsider by other geologists.
The theory became widely accepted after sea floor spreading
showing magnetic reversal in rocks was discovered in the 1960's.
Links Waves Plate Tectonics Search Questions
gcsescience.com Contents Index Quizzes gcsescience.com
Copyright © 2012 Dr. Colin France. All Rights Reserved.