You are right: this world will burn. But so will the heavens. 2 Peter 3:12 says, 'The heavens will be dissolved, being on fire, and the elements will melt with fervent heat.' But verse 13 says, 'Nevertheless we, according to His promise, look for new heavens and a new earth in which righteousness dwells.' The word 'new' does not means something that has never existed before; it means to be new in the sense of being re-made into a new form. This is clear when we read Revelation 21:5 where the Lord says, 'Behold, I make all things new.' What the Scriptures are telling us is that Jesus is going to purge the present creation with fire so that it will be clean and new--a place appropriate for the Righteous One and His righteous people. The same earth will exist, but it will be returned to a condition something like the way it was before the great flood. Just like us, the earth itself must be born of water (the great flood) and Spirit (the purging fire of God).