Revelation 8:4 & 5
The smoke of the incense, together with the prayers of the saints,
went up before God from the angel's hand. Then the angel took the censer, filled it with
fire from the altar, and hurled it on the earth; and there came peals of thunder,
rumblings, flashes of lightning and an earthquake.
The incense was mixed with the prayers of the martyrs (those that
had died for their faith). We saw, in chapter six, that when the fifth seal of the
scroll was opened it revealed these martyrs praying for judgment to come to the earth.
In this passage, God answers their prayers when the censer of fire is thrown down to the
earth. Thunder is a warning of an approaching storm and so the earth reacts to the
coming judgment. The rumblings that are mentioned is actually voices so that those on
earth know it is not simply a storm coming but it is of God. Lightning is another sign
of a storm getting close and finally the earth reacts with an earthquake.