Re: How can the inner core of the earth be solid if it is extemeley hot?

We should remember that, although the temperature increases with depth, 
the pressure also increases with depth. So, at atmospheric pressure, if we 
heated rock to 6000 degrees Celcius it would melt.  In the middle of the earth, 
however,  the pressure is 15 million times higher than our normal pressure at 
sea level, and that can compress molten rock so much that it remains a solid.

So, the inner core is solid, and it is growing with time, as the Earth's 
heat radiates into space. In some thousands of million years the outer core 
will no longer exist, and we should have a single iron core, solid, as, 
for example, Mercury, Mars and the Moon. At that time, the geomagnetic 
field will be much weaker than it is now, and the particules of the solar 
wind will strike the Earth's surface. But that is another story...

Best regards

Eder C. Molina
Geophysicist
Dept. of Geophysics
Institute of Astronomy, Geophysics and Atmospheric Sciences
University of Sao Paulo - BRAZIL