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Igneous Rocks and the Structure of the Earth.

The Earth is about 4·6 billion years old (4,600,000,000 years).
In the beginning, the Earth was very hot and molten (liquid).
The Earth cooled, and about 4 billion years ago it had cooled
enough for the first solid rock crust to form on the surface.
This first solid crust was made from the first igneous rocks
that had formed on the surface of molten magma.

What is Magma?

Magma is a thick liquid molten rock that can form within
the mantle or the crust as a result of tectonic activity.
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.
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 cool and
become solid inside the crust (see the formation of granite)
or flow from a volcano and become solid on the
surface of the crust (see the formation of basalt).

The structure of the Earth is shown in the picture below.

Structure of the Earth

At the centre of the Earth is the core, which is made
from mainly iron and nickel.
In the middle (called the inner core) it is solid.
Further out (the outer core) it is liquid.
The outer core is between the inner core and the mantle.
Waves from earthquakes give us
information about the structure of the Earth.

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.

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