Jehovah's Witness:The Watchtower Society teaches that the earth will never be destroyed?

* The Watchtower Society teaches that the earth will never be destroyed or depopulated. How can it be, then, that God says in Isa 51:6,"... the earth itself will wear out, and its inhabitants will die like a mere gnat...", and that Jesus says in Mt 24:35, "Heaven and earth will pass away...", and that John says in Rev 21:1 that he saw"... a new heaven and a NEW earth, for the former heaven and the FORMER earth had passed away, and the sea is NO MORE."?