'One third' in the Bible

The first one blew his trumpet, and there was a shower of hail and fire mixed with blood as it hurled itself upon the earth, and one-third of the earth was burned up, and all the green grass was burned up.

Then the second angel blew his trumpet, and what seemed to be a great mountain, all ablaze with fire, hurled itself into the sea, and one-third of the sea was turned into blood,

and one-third of all the living creatures in the sea perished, and one-third of the ships were destroyed.

Then the third angel blew his trumpet, and there fell from the sky a great star blazing like a torch, and it fell upon one-third of the rivers and the springs of water.

The star is called Absinthus, that is, Wormwood. So one-third of the waters turned to wormwood, and great numbers of people died of the waters, because they had turned bitter.

Then the fourth angel blew his trumpet, and one-third of the sun was cursed with a plague, and one-third of the moon, and one-third of the stars, so that one-third of them were darkened, and there was no light for one-third of the day and for one-third of the night.

Then the four angels that were kept in readiness for that hour and day and month and year were turned loose to kill one-third of mankind.

One-third of mankind was killed by these three plagues: the fire, smoke, and sulphur that kept pouring out of their mouths.