Ramban

AND G-D CALLED THE DRY LAND EARTH. The verse states that the proper name for it would be yabashah (dry land) for as the waters are separated from the sand it becomes dry. However, He called it eretz (earth) as the name which included the four elements created on the first day. The reason for this is that they were all created for the sake of the earth in order that there be a habitation for man, since among the lower creatures no one but man recognizes his Creator. in the Book of Exodus). And the gathering together of the waters He called ‘yamim’ (seas). It is as if [the word yamim, (seas) combines the two words] yam and mayim (a sea of waters), for the bottom of the ocean is called yam, as it is written, As the waters cover the sea, and likewise, And he took down the sea from off the brazen oxen. It is called “sea” because there was a large gathering of water in it. AND G-D SAW THAT IT WAS GOOD. This means that their continued existence was by His Will, and the purport is that when He clothed them with this form He desired them to be so and their existence was thus established as I have explained. This conforms to what our Rabbis have said: “Why is it not stated in reference to the work of the second day that it was good? Because the work associated with the waters was not completed until the third day. Therefore on the third day, [the words ki tov — that it was good] are repeated, once in reference to the completion of the work associated with the waters, and once in reference to [the completion of the other work of] that day.”