What is 1/3 symbolic of in Revelation 8:9?
It must be remembered that the structure of the book of Revelation is an entirely different treatment of time. It is not a neat linear chronological telling of events, but rather it is a different way of story telling that comes from a different vision of history. This approach is called recapitulative history. It means simply that the book returns to the same events recounted earlier to tell about them in a different way, each time portraying them with greater intensity.
With that in mind, we see that the three times in which judgment is poured out upon the wicked, the level of intensity increases: first, through the opening of the seven seals; then the sounding of the seven trumpets; and last, through the emptying of the seven bowls. In Revelation 6:8, the opening of the fourth seal, we are told that Death and Hades "were given power over 1/4 of the earth, to kill with the sword and with famine and with pestilence and by wild beasts of the earth." Thus, it would follow in recapitulative history that the next judgment, the sounding of the trumpets, would usher in a greater devastation -and that it does. "The devastation which the trumpets introduce is greater than that produced by the opening of the first four seals: a third of the earth is affected, not just a quarter."
(The Navarre Bible, Four Courts Press, 2003) And, as we move into the seven bowls of plagues (Rev 15-17) we witness divine justice. As the wrath of God on the followers of the beast intensifies, the punishment is increased to the total destruction of evil; and in heaven, songs of victory ring true as "the righteous rejoice to see their enemy overwhelmed and welcome the kingdom of God and the imminent marriage of the Lamb." (The Navarre Bible)