That's not fair, Smart guy, He, who proposes an alternative theory or hypothesis, not in line with the scholar ideas, has the onus of proof, That's rule nr. 1A(1) in science.
How about if I stated that the earth was hollow
and prove me wrong
This is the scholar idea:
Again, if nobody stealthily changed the physical laws for P-waves and S-waves, the mantle is not fluid but semi solid. For (sound) waves it acts as solid. For plate tectonics, hot spots and mantly plumes with dynamics measured over millions of years it acts a bit more as fluid.