The complicated history of how the Earth’s atmosphere became breathable
arstechnica.com
arstechnica.com
David Attenborough brilliantly explains the beginning of life and the role of cyanobacteria in the first episode of Life on Earth (1979), "The Infinite Variety,"[1] (in less than 20 minutes; doesn't need to be that long, but I wanted to catch him riding the mule, sooooo... strap in and enjoy).
The wiki goes on to speculate that eukaryotes were required to solve this problem, which is an enormous amount of time for such toxicity.
https://en.wikipedia.org/wiki/Great_Oxidation_Event
During the cretaceous, oxygen increased so substantially that it would be obversely toxic to modern life, too much instead of too little.
This crushing limit lasted for billions of years, until the age of eukaryotes.
This step is as much of a mystery as the Cambrian Explosion.
That’s evidence that it didn’t here, but not an explanation as to why or how.
Kudos.
Edit: this section on the oxidation catastrophe implies that plants (seemingly) grew out of cyanobacteria. They did not. Basic eukaryotes that had a mitochondria came first, then plastids came after, with integration of new organelles. Plants are more evolved than us, from this perspective.
"Despite their tiny size, immense collections of cyanobacteria that bloomed across the oceans contributed to planet-wide ecological changes over time. These impacts include: oxygenating the atmosphere, originating plants, producing oil deposits, and energy efficient metabolisms. Cyanobacteria were so successful at taking in carbon dioxide that they narrowly caused their own extinction event. Many other microbes perished, too; however, life that had adapted to use oxygen flourished."
You are likely aware that there are (about) seven major classifications of plastids, and chloroplasts are but one. Chromoplasts are the only other that I remember offhand, and all came after the mitochondria.
"Cyanobacteria live just about everywhere on Earth that sunlight reaches: cold arctic tundra, Plant cells have an organelle called a chloroplast, which can be traced back to cyanobacteria, genetically."
I did not know about the molybdenum.
Again, this is a really nice book. I would read it to my kids.
Think this is wrong. The discarded oxygen during photosynthesis comes only from splitting CO2.
https://en.wikipedia.org/wiki/Cyanobacteria#Metabolism
"In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide[77] a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria."
* I found it by searching for "oxygen"
Contrary to grandparent, in oxygenic photosynthesis, the oxygen does come from splitting water. The resulting hydride used to "charge" an electron carrier: https://en.wikipedia.org/wiki/Photodissociation#Photolysis_i...
The CO2 gets fixed into carbohydrates. Some water is generated in that process, but no molecular oxygen.
The oxygen was their waste product, and it poisoned them when the concentration grew too high.
They had to wait for natural weathering to take the oxygen out of the atmosphere before they had another cycle of flourishing.
"Cyanobacteria are a very large and diverse phylum of photoautotrophic prokaryotes... cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxidation Event and the "rusting of the Earth", which dramatically changed the composition of life forms on Earth."
Earth's atmosphere didn't "become breathable".
Rather, species evolved to survive within whatever the environment was at the time and also had an effect on the atmosphere itself, thereby killing other species in a very complicated dance.
The whole notion implied by the title is wrong.
> Biology, geology, and chemistry all worked together to make the present atmosphere.
No, no one "worked together". And Earth never was an "Alien planet".
Life evolved alongside any challenges that a changing planet posed to it. Including changes induced by organisms. Life still is evolving today and hopefully will continue to do so.
Also titles like this imply that the evolution of our planet and life is somehow guided or is directed to support humans. Or that humans are the crown jewel of evolution.
Au contraire. We are a pretty shitty product of evolution and are a danger to evolution itself since we acquired the intelligence and technology to change DNA of creatures based on our whims. (We did this for centuries through artificial selection. Now we can do it more directly)