Question

How do we know that the structure of the earth exists?

Answer 1

See explanation.

Explanation:

All matter of the Earth are attracted toward's the center of the

Earth, by the force that is proportional to the mass ( m ) of the

matter and is inversely proportional to square of the distance

( `1/r^2` )..

This force creates higher-pressure, and consequently higher

temperature, as the distance from the center decreases.

So, the density ( on the average ) of the layers increase, towards the

center.

Thes density variations are revealed by the vast, compiled from

the research findings on propagation of primary and secondary

seismic waves, just after earth tremors and earthquakes, over

centuries.

Important note:

Despite that, as `r to 0, 1/r^2 to oo`. the resultant force towards the

center is a null or near-null ( `epsilon`-magnitude ) force. The

components, in infinitude, are self balancing in this near-spherical

Earth.