Rev 21:1
Then I saw a new heaven and a new earth; for the first heaven and the first earth passed away, and there is no longer any sea.

The simple answer is that the first heaven and the first earth passed away. God first created the earth to be a place for mankind to live. Sin has corrupted the earth and our universe so God destroys them.

Rev 20:11 And I saw a great white throne and Him who sat upon it, from whose presence earth and heaven fled away, and no place was found for them.
NAS

Barnhouse wrote, "There is to be an end of the material heavens and earth which we know. It is not that they are to be purified and rehabilitated, but that the reverse of creation is to take place. They are to be uncreated. As they came from nothing at the word of God, they are to be sucked back into nothingness by this same word of God" (Revelation: An Expository Commentary [Grand Rapids: Zondervan, 1971], 391).