Thank You Cyannobacteria!

What would you call the emergence of a bacterial entity that actually put off as waste a poisonous gas and eventually killed off all other forms of life on the planet? The life of the party, baby!

One life form back in the day, and I mean way fucking back in the day, like more than a billion years ago, emerged as being quite effective at replicating itself. It had two secrets: the first was that it used the sun's energy for food; and the second was that it expelled poisonous gas as waste, thereby dealing effectively with their neighbors.

"Using the sun's energy for food" is an oversimplification of the photosynthesis, but the idea's set: something is directly using the sun, like a parasite of sorts (not really, but...) The gas that these little suckers used to murder off everything else was oxygen, quite the nasty poisonous gas to many an early living thing.

Once the oxygen really started to fill the atmosphere, the die off of the other organisms quickened, all the way until today, where the only life-forms that don't use oxygen are living down in thermal vents at the bottom of the ocean or living in random caves near sulfur vents.

Those little bastard bacteria that killed off so many others with their poisonous gases are called cyannobacteria, and there are still types around today. All life that uses oxygen have them to thank for getting the planet ready for us. Animal life developed as a parasite of plant life, and plants just yse sunlight, and we all need to thank those little cyannobacteria.