NITROGEN
WATER
VAPOR
AMMONIA
METHANE
CARBON
DIOXIDE
HYDROGEN
NITRIC
OXIDE

Aha! CARBON  CYCLE is what  makes earth "Earthy"!

But there would be no life without _____ and the gas we breathe: Oxygen

2.5 Billion years ago there was no oxygen instead there were 5 gases. Find those and you'll get your word!