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Layers of the Earth

The Earth is divided into three chemical layers: the core, the mantle
and the crust. The core is composed of mostly iron and nickel and
remains very hot, even after 4.5 billion years of cooling. The core is
divided into two layers: a solid inner core and a liquid outer core.
The middle layer of the Earth, the mantle, is made of minerals rich in
the elements iron, magnesium, silicon, and oxygen. The crust is rich
in the elements oxygen and silicon with lesser amounts of aluminum,
iron, magnesium, calcium, potassium, and sodium. There are two types
of crust. Basalt is the most common rock on Earth. Oceanic crust is
made of relatively dense rock called basalt. Continental crust is made
of lower density rocks, such as andesite and granite.

The outermost layers of the Earth can be divided by their physical
properties into lithosphere and asthenosphere.

The lithosphere (from the Greek, lithos, stone) is the rigid outermost
layer made of crust and uppermost mantle. The lithosphere is the
"plate" of the plate tectonic theory. The asthenosphere (from the
Greek, asthenos, devoid of force) is part of the mantle that flows, a
characteristic called plastic behavior. It might seem strange that a
solid material can flow. A good example of a solid that flows, or of
plastic behavior, is the movement of toothpaste in a tube. The flow of
the asthenosphere is part of mantle convection, which plays an
important role in moving lithospheric plates.
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[1][LINK]
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References

1. http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/introduction.html
2. http://volcano.und.nodak.edu/vwdocs/vwlessons/atg.html
3. http://volcano.und.nodak.edu/vw.html
4. http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part2.html