There was a time when those farts destroyed the world https://en.wikipedia.org/wiki/Great_Oxidation_Event
Nowadays plants need to sniff their own farts or they wouldn’t be able to use the energy they stored.

People like to say plants “eat sunlight” and “breathe CO2”, but actually, it’s closer to the opposite! They crack off the carbon in the air to build themselves and release oxygen, similar to the way we turn food into fuel and poop, and power the process using photosynthesis, similar the way we power our cells with oxygen.