A solid nickel-iron core was invented for two reasons, to allow the earth a sufficient mass required of it by Newtons formula, and to allow for something which could be a big magnet. Of course, molten nickel and iron can't be a permanent magnet, or even if heated above around 800 degrees. So, in a fit of creative thinking, schmience pictured the core being under such enormous pressures (generated by that same formula) as to force solidification. Last time I checked, I didn't know of how any liquid could be turned to solid in this way. In fact, when I checked, putting something under pressure usually raises its temperature. In that equation,
d is distance. It is also written as
r, or radius squared. What the equation sez is the F, or force of gravity, decreases as the inverse square of the radius, starting at the center of mass. What the thinking has been is that as one proceeds below the surface, the pressures increase with the shortening of the radius and the increased mass overhead. That equation would, if carried to the ridiculous, say that gravity is infinitely increased at the center of mass where the radius becomes zero, while in reality, at the center, all mass is outward, and if it is mass that is the source of the force (which I seriously doubt), all the planet's mass would be pulling away from the center, and hence, the center should be a vacuum. But I reject the formula, because I believe F is a product of an ether vortex, but then, schmience , after Michelson/Morley, 1895, said there ain't no ether, nohow. So, I continue to be a crackpot whose ideas are too whacked out for any serious consideration.
http://www.flyingdisk.com/newtons.htm