Simplicio: From the oldest records we have it that formerly, at the Straits of Gibraltar, Abila and Calpe were joined together with some lesser mountains which held the ocean in check; but these mountains being separated by some cause, the opening admitted the sea, which flooded in so as to form the Mediterranean. When we consider the immensity of this, and the difference in appearance which must have been made in the water and land seen from afar, there is no doubt that such a change could easily have been seen by anyone then on the moon.
(From the Dialogue Concerning the Two Chief World Systems)
By giving these words to Simplicio, Galileo clearly is not trying to argue for this conclusion. But as neither Salviati nor Sagredo object, it also seems that this opinion was generally held among the educated Venetians in 1632 and that Galileo either did not doubt it, or did not care to contest it.
What is most surprising is that geologists today believe this to be true. The event, called the Zanclean Deluge, happened more than 5.3 million years ago. Therefore it seems impossible that the people of Galileo's time could have known it based on any good evidence.
It seems to have been a lucky guess by Pliny the Elder, hence the principal relevance to our present interest. The Dialogue does not reference the Bible at all, and barely glances at religion. The debate is between the theoretical insights of Copernicus and empirical observations of Galileo, on the one hand; and the authorities of classical antiquity on the other. I'm sure that Galileo could not have directly challenged the Bible and expected to avoid being tortured to death. Nevertheless, while I am not an expert on his time, it does seem clear that Old Testament literalism was not the prevailing intellectual fashion, but rather fealty to Aristotle and the classical philosophers.
Indeed, Galileo had presumed he could convert the church authorities to his cosmology, and had actively sought them out to make his presentations. He was very unpleasantly surprised by the reaction he got. I'm sure the authority of the Bible was salient in his hearings before the Inquisition, but I do not think it was Biblical literalism the church was concerned to defend so much as the metaphysical implications for the relationship between God and humanity of moving the earth from the center of the universe.
And they were right to be afraid of this. Galileo, in fact, did not put the sun at the center of the universe either, as he states in one of the most astounding passages in the Dialogue, to be considered anon.