Everyone knows when you expose a magnet to extreme heat it looses its magnetism.
If you believe in the 1000 miles an hour spinning ball which apparently is very hot at its centre (forever) a magnet does not function.
Here is the difference, but it is true that we don't know much.
Consider the weight at the center of the earth. This is an extremely difficult to calculate accurately. However, we know from experience that if you lower a spherical "diving bell" down into the ocean by cable from a ship, and allow it to fill up with water a couple of miles down and then seal it, that when you bring it to the surface and open it, excess water bubbles out.
This means that water is actually compressed by its own weight at only a couple of miles down. So, how much is liquid iron compressed at near 4,000 miles down - the center of the earth - with the whole weight of the earth on it from all sides? Nobody knows. Nobody can even begin to calculate the pressure. And nobody knows how magnetism acts in liquid iron under that much pressure. We have no way to measure magnetism under pressures like this.
In addition, when you calculate a 1,000 MPH spinning globe that is the size of the earth, the strength of gravity easily overcomes the centrifugal force. The size of the earth makes the twisting motion that would normally be caused by inertia to be so small that it isn't noticed.
For the once how are a bit behind times, check sig for a starter.
Exciting times await. Very soon a full functional map and model will be at hand.
Seismologists measure the vibration at various places on the earth. They don't know exactly what materials in the ground the vibrations caused by earthquakes must go through to get here or there. But through testing and much observation, it is easy to see that the earth is globular, just by how long it takes for earth vibrations to get from one point to another.
For example. If there is a 7.8 magnitude earthquake in Ecuador, the moment of the quake seismologists all over the world are informed by radio that the quake happened. They don't have to wait for days, wondering where those vibration on their seismographs came from.
Seismology is a reasonably exact and accurate science, and it shows us that the earth is globular, by the rate at which earthquake and volcano vibrations reach different areas on the globe, and by the inter-communication of seismologists.