Adam Clarke on Genesis 6:13

I will destroy them with the earth - Not only the human race was to he destroyed, but all terrestrial animals, i.e. those which could not live in the waters. These must necessarily be destroyed when the whole surface of the earth was drowned. But destroying the earth may probably mean the alteration of its constitution. Dr. Woodward, in his natural history of the earth, has rendered it exceedingly probable that the whole terrestrial substance was amalgamated with the waters, after which the different materials of its composition settled in beds or strata according to their respective gravities. This theory, however, is disputed by others.