7The first sounded, and there came hail and fire, mixed with blood, and they were thrown to the earth; and a third of the earth was burned up, and a third of the trees were burned up, and all the green grass was burned up.
Rev_8:7 "and there came hail and fire, mixed with blood" Much of the imagery is drawn from the Egyptian plagues. This passage is an allusion to Exo_9:24. It is also possible that this is taken from Eze_38:22, the overthrow of Gog's invading army.
▣ "and a third of the earth was burned up" This limited, but substantive, percentage is mentioned quite often in the next few chapters (cf. Rev_8:7-12; Rev_9:15; Rev_9:18; Rev_12:4). The second series of judgments is more intense than the first (cf. Rev_6:8, where one quarter is mentioned). YHWH is still attempting to reach sinful mankind by means of physical plagues (cf. Exodus 7-11; Deuteronomy 28-29), but they would not respond in repentance and faith!
▣"and all the green grass was burned up" This must refer to the complete destruction of the green grass within the one-third area, because green grass is protected in Rev_9:4.