Chapter 21:  The New Heaven and Earth:

In Chapter 20, Satan was overthrown and cast into the lake of fire, along with death and Hades.  Those whose names were not found written in the book of life were also cast into the lake of fire.  Those who overcame (whose names were written in the book of life) were not hurt by the lake of fire (the second death).

Let's continue with Chapter 21:

And 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. Revelation 21:1 (NAS)

Question:

Chapter 21 begins with John seeing a new heaven and a new earth.  According to Revelation 21:1, what had happed to the first heaven and earth and the sea?