Which earth are you referring unto? You have the first 'earth' being the physical body (breadth, and length, and depth, and height) of space which was created in the beginning or the second 'Earth' being the the celestial body of mass that abodes in the expanse of space upon which we dwell.
Foundation in the literal sense is the supporting base upon which a object is built.
The first earth, or the physical body of space we call the universe is hung upon nothing, which does not mean that it is nothing, it is nothing that exists in this universe. You could say it is light, but it is light that has not been seen, nor can be seen.
It can only be perceived by the substance that the supports the celestial bodies of mass that exist within this universe. Which again is nothing, in the sense it is not is not a form of mass, which some still consider to be nothing since anything that isn't mass doesn't exist in their opinion, yet it can been perceived by the presence of mass.