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The lifespan of your average species is about a million years. A brief existence before entering the fossil record is the norm, with a few notable exceptions. Tardigrades, sharks, and sponges have long outlived their expiration dates.A few billion years ago, Earth was completely taken over by the MCU’s lamest supervillains, and they’re still here. Small but mighty, its descendants would sooner cause another mass extinction event before being taken out by one.This Week's Moment of Filth… The Great Oxygen Catastrophe, or how cyanobacteria pissed in evolution’s dirty whore mouth.There are–wrong– people who will argue that we can’t do much about the climate because it kinda sorta changes naturally and has always done so. It’s managing itself, far outside the control of one species. This enormous, stable, life-sustaining, oxygen-rich atmosphere couldn’t possibly be changed solely by human activities to a point that hurts us.Which begs the question, how stable is the level of oxygen in the air? This rock wasn’t plunked into the great wide universe cooking show style, all ready for us to enjoy without the baking time. There have been three fairly distinct atmospheres, and it wasn’t until a long simmer through the third one that oxygen levels became consistently compatible with human life.The Hadean Eon was so named because our newly birthed orb was hotter than Satan’s cheesed ballsack. It came with an early atmosphere composed of gasses from our almost-a-sun’s nebula, mainly hydrogen. Other than a pinch of zircon, there’s a whole lot of nothing solid left kicking around from the first half billion years of the planet. Even with our current capabilities, this presents quite a few difficulties in testing hypotheses about the era.Amidst the intermittent asteroids showers and airing out that ‘new planet smell’ with some light volcanic outgassing, the Archaean Eon ushered in the second atmosphere. It was an improvement in terms of ‘not a magmalicious hell sphere’ (my band name), but I’d still steer clear of this eon with your time machine. Though the finer points are still debated, the atmosphere had negligible oxygen, a bunch of nitrogen, and simply assloads of carbon dioxide.Which wasn’t a problem for the first single-celled beastie that sprang into existence. Primitive single-celled organisms likely used precursors to fermentation or other types of anaerobic processes for energy. Everyone was getting along fine without any of that pesky oxygen.The young planet kept busy rearranging freshly baked proto-continents. Then, some new forms of life popped up around 3.4 billion years ago that would eventually usher in our third atmosphere: photosynthesizers.Anoxygenic photosynthesis was the earliest form of the process and, as the name suggests, didn’t produce oxygen as a waste product. So for a little while (on a geological timescale) things kept right on going. There’s debate on when oxygenic photosynthesis started, but somewhere around 2.4 billion years ago is when the atmosphere started getting lively.Cyanobacteria, the first known organisms to have produced oxygen, all but took over. With an abundance of fuel from sunlight and CO2 and very little in the way of competition, it would be an insult to our microscopic green overlords to call this anything other than total planetary domination.This was nearly to its own peril.It’s not that the planet’s oxygen level was suddenly all that high. On the contrary, it was still a fraction of what it is now. But as with all things in toxicology, poisons are dose and species specific. It didn’t take a lot of oxygen to spell death for the anaerobes. Oxygen is also highly temperamental, readily reacting with just about goddamn everything. Dissolved iron in the oceans oxidized, leaving a coating of rust on the seafloor. It also reacted with gasses in the atmosphere. Methane readily oxidized into carbon dioxide, which was both a weaker greenhouse gas and fuel for the blue-green menace.“Ms. Auntie SciBabe,” I hear the environmentally-minded amongst you wonder, “isn’t reducing greenhouse gasses a good thing?” We think of it as a good thing today because we’re producing too much of it. But with unchecked cyanobacteria growth, the greenhouse effect wasn’t a concern. Quite the opposite, in fact.As cyanobacteria binged on most of the available atmospheric carbon, dousing the planet with oxygen, it found itself very nearly alone on a cold planet of its own making. The Huronian Glaciation, the first and longest known ice age at 300 million years or so, was ushered in largely by these microscopic giants.The Great Oxygenation, between the oxygen itself and the subsequent ice age, is suspected to have pushed up to 99% of species into extinction. It carved most of the old branches off the tree of life, pushing evolution in entirely new directions.Though the descendants of those original cyanobacteria are still kicking around causing trouble here and there, it seems unlikely they’ll contribute to another mass extinction event anytime soon. However, it seems far less likely that there will ever be an Earth without cyanobacteria.This has been your Moment of Filth, pretty sure that, once again, there’s one species disproportionately affecting the climate.