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Igneous Rocks - History.
The Earth is about 4·6 billion years old (4,600,000,000 years).
The Earth was very hot
and molten.
As it cooled, the first solid rock
crust appeared about 4 billion years
ago.
This solid crust (the first
igneous rocks)
formed on the surface of molten
magma.
Magma is a thick
liquid molten rock (like
treacle)
which can form within the mantle or the crust.
The mantle mainly contains hot
solid rock
which can flow only very very
slowly.
This slow movement makes sections (plates) of
the crust collide
or slide past each other (see
Plate Tectonics on the GCSE Physics site).
The enormous amount of energy which is released when plates collide
is sufficient to melt parts of the mantle or crust and
form magma.
The magma can then solidify inside the crust (see granite)
or flow from a volcano and solidify
on the surface of the crust (see basalt).
At the centre of the Earth
is the core, which is made of
iron and nickel.
In the middle it is solid (the inner
core).
Further out (the outer core) it is liquid,
between the inner core and the
mantle.
The oldest rocks are
igneous rocks.
They are called igneous from the
Latin ignis, meaning fire,
like ignite - set fire to.
The Earth's crust,
oceans and atmosphere are the sources
of all raw materials from
which everything we see around us is
made.
Headings Igneous
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Copyright © 2008 Dr. Colin France. All Rights Reserved.