How much pressure exists at the Earth's inner most core?
Does this have an effect on the intensity of earthquakes?
What purpose does the magma serve to the earth?
If I recall correctly the pressure at the center of the
earth is around 5 million times atmospheric pressure (the
15 pounds/square inch that we breathe and live in). However
that really does not have much effect on what happens up
here near the surface. You may have heard about earthquakes
having an epicenter - this is where the earthquake really happened
and is usually between 0 and 50 miles below the surface of
the earth. Even 50 miles is pretty small compared to the
radius of the earth (4000 miles), so the pressure in the earth
at even the deepest earthquakes is much less than it is at
the center of the earth - the earthquakes are much closer
to us up on top than to the core way down below.
The other thing that happens as you go down deep is that
it gets pretty hot - thousands of degrees. The magma you
mentioned is usually the name for the first layer of the earth
below us, containing hot and molten rock that sometimes comes
up to the top through volcanoes and similar events.
This is actually an "earth science" question so you might get
a better answer by asking over there.
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Update: June 2012