How certain are we (current science) that our conclusion regarding the composition / architecture / structure of the inner /deepest part of the planet?

From what I have read, we have not had any probes too far into the earth.

I remember someone saying that we know more about space than we do about the earth.

I dont know if I should have listened to the guy.

I do understand that the article references distributed readings over long timespans of seismic data that allows scientists to establish the current view.