I answer that, There are many opinions on this question. For some say that all the elements will remain as to their matter, while all will be changed as regards their imperfection; but that two of them will retain their respective substantial form, namely air and earth, while two of them, namely fire and water, will not retain their substantial form but will be changed to the form of heaven. In this way three elements, namely air, fire, and water, will be called "heaven"; although air will retain the same substantial form as it has now, since even now it is called "heaven." Wherefore (Apoc. 21:1) only heaven and earth are mentioned: "I saw," says he, "a new heaven and a new earth." But this opinion is altogether absurd: for it is opposed both to philosophy---which holds it impossible for the lower bodies to be in potentiality to the form of heaven, since they have neither a common matter, nor mutual contrariety---and to theology, since according to this opinion the perfection of the universe with the integrity of its parts will not be assured on account of two of the elements being destroyed.
Consequently "heaven" is taken to denote the fifth body, while all the elements are designated by "earth," as expressed in Ps. 148:7,8, "Praise the Lord from the earth" and afterwards, "fire, hail, snow, ice," etc.
Hence others say that all the elements will remain as to their substance, but that their active and passive qualities will be taken from them: even as they say too, that in a mixed body the elements retain their substantial form without having their proper qualities, since these are reduced to a mean, and a mean is neither of the extremes. And seemingly the following words of Augustine (De Civ. Dei xx, 16) would seem in agreement with this: "In this conflagration of the world the qualities of the corruptible elements that were befitting our corruptible bodies will entirely perish by fire: and the substance itself will have those qualities that become an immortal body."
However, this does not seem probable, for since the proper qualities of the elements are the effects of their substantial form, it seems impossible, as long as the substantial forms remain, for the aforesaid qualities to be changed, except for a time by some violent action: thus in hot water we see that by virtue of its species it returns to the cold temperature which it had lost by the action of fire, provided the species of water remain. Moreover, these same elemental qualities belong to the second perfection of the elements, as being their proper passions: nor is it probable that in this final consummation the elements will lose anything of their natural perfection. Wherefore it would seem that the reply to this question should be that the elements will remain as to their substance and proper qualities, but that they will be cleansed both from the stain which they contracted from the sins of men, and from the impurity resulting in them through their mutual action and passion: because when once the movement of the first movable body ceases, mutual action and passion will be impossible in the lower elements: and this is what Augustine calls the "qualities of corruptible elements," namely their unnatural dispositions by reason of which they come near to corruption.