What is the Earth made of?
The earth formed approximately 4.5 billion years ago. It was
so hot when it formed that it was made up of molten (melted) rock.
While the earth was cooling, the chemicals in the earth became
differentiated, or separated. The lighter materials remained
close to the surface making up the crust. The heavy, dense
materials created a core at the center of the earth, composed
of mainly nickel and iron. In the middle is the mantle,
which contains less dense material than the core, but more dense
material than the crust.
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Aren't all rocks the same?
There are many different kinds of rocks. The three main groups
of rocks include:
- Igneous rocks: formed from the cooling of magma (under
the surface) or lava (on the surface).
- Sedimentary rocks: formed when mineral grains cement
together. (Ex: sand cementing together to form a new rock
is called sandstone)
- Metamorphic rocks: formed when either sedimentary or
igneous rocks have been changed because of high temperatures,
high pressures, or both.
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Lava flow of Pu'
u 'O'o volcano, Aug 1990. Lava cools to
become igneous rock.
(Photo taken by T. Maddox)
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