Ok nerds I know I should finish my Charizard drawing but I’m procrastinating so sit down and grab a drink, I’m here today to preach about our lord and savior,
it’s just a bunch of dead rocks…? Rude. Ok Stromatolite literally means layered rocks but it’s actually a solid structure built by a colony of living cyanobacteria (blue-green algae).
Um so what. Here’s the fun part, our little friends there basically stick together their entire life, drenched in their own microscopic equivalent of sweat and shit, because they’re best buds like that. All this sticky excretion also traps sediment from their surrounding. It’s like stationary Katamari Damacy. Except bit shitty.
Ew. Gross. Didn’t your parents teach you to behave around the elderly? Some of these guys have been around for 2000-3000 years, andtThe cyanobacteria that build these pretty structures are known to be similar to lifeforms found 3.5 billion years ago. So they’re effectively a simulation of Precambrian life. Sorta.
Um. Cool. What are they good for? Remember when I said they basically live in their sweat and shit and fossilize it all together? Like tree rings, their layers tell us about the environment of a certain era. Just like when your bestie dug through your browsing history to see what you’d been watching all week and which restaurants you ordered your food from.
Except they last thousands of years. So in 100 years, when your hopes and dreams are long dead and forgotten, they will still be chillin, keeping a record of time like the true nerds they are.
Whatever I’m done here you nerd. Hey. I’m not done. Did I tell you that they photosynthesize? If you don’t think green little thingies literally devouring sunlight to stay alive while farting out oxygen for you ungrateful metazoan to stay alive and scroll this website is the raddest thing on Earth, I don’t know what’s wrong with you.
Who are you? Get out of my way, there’s some nerd telling me some bullsh-
But check it out. Stromatolites are made of cyanobacteria, the organisms responsible for the rad-ly named Great Oxygenation Event. Early Earth had virtually no oxygen in its atmosphere, and any that was produced immediately reacted with iron dissolved in the ocean to create iron oxides that were deposited in sediment. As cyanobacteria produced oxygen, cyclical variations in the amount of oxygen available produced striped rocks called Banded Iron Formations, which alternate between iron oxide rich layers and iron poor layers.
Oh my god, where are you people coming from? Why do you even care about ancient dead things?
Cyanobacteria did all this for a good couple million years, happily churning out oxygen on an otherwise anoxic Earth…
…until they ran out of iron.
Suddenly, oxygen levels skyrocketed. All of life on Earth, including cyanobacteria themselves (and all other photosynthetic organisms, for that matter), had evolved to operate in anoxic environments. Cyanobacteria (which, don’t get me wrong, include a great many other species besides the stromatolite-making ones) were therefore responsible for Earth’s first mass extinction.
…So if they evolved in low-oxygen environments, why are these ancient murder blobs still around?
Glad to see you’re coming around on them.
No, I’m not. Nevermind, forget I ask-
Different groups of photosynthetic organisms have different coping mechanisms for photorespiration, the thing that makes photosynthesis in the presence of oxygen less efficient, but they are all much stupidier than, say, a system that uses something besides RuBisCo. We can therefore take it as (yet another) piece of evidence that photosynthesis originally evolved in anoxia. Picture cyanobacteria going, “Shit, shit, shit, how do we fix this??? :(”
Are you done yet? Even if you’re not, I’m leaving now. Again.
WAIT WAIT WAIT, I HAVEN’T EVEN TOLD YOU ABOUT HOW THE EXTINCTION OF 80% OF STROMATOLITES IS CORRELATED WITH THE CAMBRIAN EXPLOSION BECAUSE MULTICELLULAR GRAZERS EVOLVED, OR HOW THEY TENDED TO BE MORE COMMON DURING EXTINCTION EVENTS BECAUSE THE STUFF THAT ATE THEM WAS DYING OUT, OR HOW TODAY THEY’RE ONLY FOUND IN HYPERSALINE ENVIRONMENTS BECAUSE THEY WON’T GET EATEN THERE
