Over the ages, survivability for just about every species on this planet drops to zero. There are a few notable exceptions. There was the time a few billion years ago when Earth was taken over by the MCU’s lamest supervillains. Small but mighty, its descendants would sooner cause another mass extinction event before being taken out by one.
Today’s Moment of Science… 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. Any changes to this positively enormous life-sustaining atmosphere due solely to human activities couldn’t possibly hurt us.
Which begs the question, how in sweet deep fried Baby Jesus’ name were we blessed with this oxygen rich atmosphere in the first place? This rock wasn’t plunked into the great wide universe cooking show style, ready for us to enjoy without the requisite baking time. There have been three fairly distinct atmospheres, and it wasn’t until a long boogie 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 smidge 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.
Sometime amidst a dusting of asteroids and airing out that ‘new planet smell’ with some light volcanic outgassing, the second atmosphere was in full swing by the Archaean Eon. It was an improvement in terms of ‘not a ball of magma-y fuck shit hell cunt’’ (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 likely had a severe lack of breathable 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-ish 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 food 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 a percentage 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. It also reacted with other gasses in the atmosphere. Methane would oxidize into carbon dioxide, a swap of a stronger greenhouse gas for a weaker, more delicious one for the blue-green menace.
As cyanobacteria binged on most of the available atmospheric carbon, dousing the planet with oxygen, it found itself mostly 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 small 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 into 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 Science, pretty sure that, once again, there’s one species disproportionately affecting the climate.
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