|Why is the inner core solid even though it is
hotter than the outer core?
The inner core is indeed hotter than the outer
core. However, the PRESSURE on the inner core is
greater than the pressure on the outer core and
the melting point of iron, the main constituent of
the core, INCREASES as the pressure goes up. So,
because the pressure effect overrides the
temperature effect, the inner core is solidified.
We also can speculate that the inner core
began to freeze (solidify) about 1 or two billion
years ago. the inner core makes up only 1% of the
mass of the Earth; the outer core makes up about
32% of the mass of the Earth.
The inner core is solid because it is made
dense, or heavy, materials - like iron and
nickel. Even though it is very hot, these
don't "melt" very easily, so they stay
It turns out that many materials can be a solid at
a higher temperature if the pressure is also
higher. So, even though it is hotter in the inner
core, the pressure in the core is also higher, and
you can have solid iron-nickel instead of
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