Does the Earth have a semi-solid body at its core because of lower pressure at the center of the Earth?

Question

I have read that the Earth has a semi-solid iron body at its core, even though that object is surrounded by liquid magma.... I'm wondering if this is because of a pressure (and resulting temperature) differential -- or if there is another reason.

1) Since the forces of gravity of a sphere are at equilibrium at the center of the sphere -- doesn't that mean that the pressure at the mass center of a planet would be zero -- since there would be no "force" to be distributed at that area?

If the answer to #1 is true, then it leads to these further questions....

2) At what point between the surface and the center of the planet would the pressure be the greatest?

3) Would the depth in the Earth, at the max. pressure point specified in #2, be where we would expect to find the central layer of the Earth's magma? -- (Since pressure generates heat, wouldn't that be the hottest point; from a "pressure variable only" view?).

4) Shouldn't it actually be cooler at the Earth's mass center, than at the max. pressure point specified in #2 -- since the pressure is lower at the mass center?

4.a) And could that center temperature be enough cooler that it allows a core body to semi-solidify?

Answer 1

1) Maximum pressure is in Earth's mass center. As, you say, all gravity forces cancel each other out at the center since the mass of Earth is symmetrically distributed around you. But the pressure in one point does not just pedpend on gravity in that point. Pressure is due to the weight of everything above you, and in those points, gravity is definitely not zero. Pressure is the integral of gravity (multiplied by mass density) from where you are all the way up into space. Hence, the pressure gradient is proportional to gravity and the fact that gravity is zero in the center of Earth is consistent with it being the pressure maximum.