Hello and welcome to Microbe Monday! This will be a more simple one because I am not feeling well this morning. I had work stress dreams all break long so I've convinced myself I'm going to need to fight Bayle the Dread immediately after getting off the bus today.

Today I want to talk about the topic that got me into microbes in the first place: photosynthesis and its consequences. When I was a foolish child, I believed plants were my special interest. Of course, by interrogating that interest enough, I realized my fascination was largely with their metabolism.

Which they mostly just borrowed from bacteria. Chloroplasts are endosymbiotically incorporated bacteria, actually. Basically, 16S RNA sequencing shows those lil guys are sort of cyanobacteria, genetically speaking.

Cyanobacteria have perhaps had a more dramatic effect on the earth than any other organism. I genuinely cannot think of a more significant organism. Even the massive anthropogenic ails capitalism has inflicted upon the world pale in comparison to the scale of the changes cyanobacteria wrought.

Some 2.4 billion years ago, the earth began to rust. Early cyanobacteria, some time earlier, developed a silly little trick: taking in sunlight and converting its energy to food. I could talk about photosynthetic pathways forever but here's the important part: It's a part you almost certainly know. Oxygenic photosynthesis, the kind they and most "well-known" photosyntheitc organisms use, makes oxygen! How lovely! It makes the stuff we breathe! Yay! Woo!! Hurray!!! (Also, while we're here, a minority of oxygen is produced by trees/plants. Most actually comes from marine microbial sinks. Just another reason to thank your local weird green scum.)

Anyway, early earth. 2.4 billion years ago. The thing about it is, uh. Cellular respiration. that thing we use to make energy currency? It's not really in vogue yet. It requires oxygen, and there's not much of that around. Thank God, too, because it's terrible for the overwhelming majority of life on earth. Why, oxygen is practically a toxic gas. It's so reactive! It can rip organisms apart effortlessly. It oxidizes just about everything it touches. I mean, it's a good thing we've got so much pure iron laying around in the world anyhow. What little oxygen we do run into can pal around with that.

Hey hang on what did you say the cyanobacteria were doing again? Uh huh. Oh cool! The sun. Love that for them.

Hey. What. What was that about oxygen.

And so, driven by massive success of their new metabolic strategy, cyanobacteria underwent rapid population growth. "Stromatolite" fossils are actually left over from this period. Big ol rocks from the sheer scale of these bacterial biofilms. They began pumping out massive amounts of oxygen as a byproduct of their photosynthesis.

I really want to emphasize the scale of this. Back then, the earth had a reducing atmosphere. In essence it was an "oxidizer sink" with plenty of atmospheric compounds to get oxidized, making oxidizers like oxygen practically nonexistent. Anyway oxygenic photosynthesis singlehandedly turned the atmosphere into an oxidizing atmosphere.

So yeah they kinda just flood the atmosphere with a toxic gas til it saturates the atmosphere, rusts the iron deposits (that's where those cool red rock formations come from), permeates just about every single oxygen sink there is til it just rests in the atmosphere. It kills off a lot of cyanobacteria, actually, because a lot of those little guys couldn't even handle oxygen. Cellular respiration really comes into fashion around this time, and aerobic organisms become extremely common.

Despite the abject destruction of this event, it's necessary for life as we know it. Oxygen, volatile and terrifying as it may be, is an extremely good oxidizer, hence the name. It permits some gnarlier chemical reactions, even if it does kinda slowly wear away at our molecular mechanisms. It allows for bigger, less efficient, weirder, and more diverse organisms to emerge.

I think the main thing I want to emphasize is that oxygen isn't just sitting there. It is dynamic and reactive. We only have what we do in our atmosphere by the result of continuing biological processes. The world lives and breathes with us.

Once again a strange and novel organism floods the world with gas made toxic by the dosage. Once again they make the world unlivable for themselves and others. Once again the world can recover. It can go on without them, and grow stranger for it.

But this isn't a natural byproduct of their existence. The world has been through worse than what they can inflict. They can think; they can fight. Some can see the cause, laughing up on their bloodstained belfries. The air grows feverish but they still have time. And maybe not enough but they are children of disaster! They inhale the vapors that remade the world. Revolt is in their blood. Maybe, maybe, maybe.

Happy Microbe Monday. Be well on this rustriddled earth!