The complicated history of how the Earth’s atmosphere became breathable

https://arstechnica.com/science/2023/05/the-complicated-history-of-how-the-earths-atmosphere-became-breathable/

by Brajeshwar • 3 years ago

78 33 3 years ago

Maursault• 3 years ago

Life began in that alien environment, and at some point between 3.2 and 2.8 billion years ago, cyanobacteria began to use sunlight to split hydrogen from water, discarding oxygen as waste.

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).

[0] https://www.dailymotion.com/video/x2i43qc?start=673

yarg• 3 years ago

The air was never unbreathable in any meaningful sense - it was altered in a way that provided an abundant new resource that permitted the evolution of new forms of life.

chasil5• 3 years ago

The "oxygen catastrophe" made the air toxic in ways that life could not evolve to cope with at that time.

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.

namaria2• 3 years ago

Life doesn't evolve to cope with anything. Life evolves as it adds variety and some of it gets cut down by the environment. Narratives implying teleology are misleading and wrong.

beders• 3 years ago

It's a terrible title and a terrible article altogether.

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)

fimbulvetr• 3 years ago

That's not the implication I got at all. Coupled with the photo, it really did seem like it would be an "Alien Plant" had I been able to be there. As far as "working together" - wow, you really look that literally. I don't think he meant they were conspiring by text on whatsapp.

qubex2• 3 years ago

Even the title is absurd: the atmosphere didn’t become breathable — life evolved to breathe the atmosphere.

NoahKAndrews• 3 years ago

There's an inferred "to us"

pfdietz4• 3 years ago

It's not clear why the Earth's oxygen has been somewhat stable since the Precambrian. If you kill all plants, oxygen goes away (reacting with reduced materials exposed by erosion and released in volcanism) in just a few million years. It could be an observer selection effect: if it had ever dropped too low in that time, we wouldn't be here now.

joshuahedlund• 3 years ago

It could be an observer selection effect: if it had ever dropped too low in that time, we wouldn't be here now.

That’s evidence that it didn’t here, but not an explanation as to why or how.

pfdietz4• 3 years ago

It could just be dumb luck. Ordinarily we reject hypotheses that require very rare outcomes, but observer selection implies we shouldn't do that.

thangalin• 3 years ago

My book touches upon the great oxygenation event, relating it to the production of oil deposits, which we burn at alarming rates:

https://impacts.to/downloads/lowres/impacts.pdf#page=11

chasil5• 3 years ago

This is actually a very attractive book from a graphical design perspective. The content also looks enticing.

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.

ur-whale• 3 years ago

I don't get the concept at all.

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.

phkahler• 3 years ago

Yeah, all those animals flopping around gasping for air until finally the air became breathable... ;-)

chasil5• 3 years ago

It was actually prokaryotes that were dying in their own waste.

classified• 3 years ago

It has always been breathable, it just changed for who.

s1artibartfast• 3 years ago

The article and author assumes that the readers are humans, not going to Cellular life forms.

chasil5• 3 years ago

Carbon dioxide was breathable fuel for cyanobacteria prokaryotes.

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."

https://en.m.wikipedia.org/wiki/Cyanobacteria

so-and-so• 3 years ago

Life began in that alien environment, and at some point between 3.2 and 2.8 billion years ago, cyanobacteria began to use sunlight to split hydrogen from water, discarding oxygen as waste.

Think this is wrong. The discarded oxygen during photosynthesis comes only from splitting CO2.

fsckboy• 3 years ago

maybe they are referring to this?*

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"

citrate05• 3 years ago

If you use hydrogen sulfide as an electron donor, you end up liberating sulfur, not 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 complicated history of how the Earth’s atmosphere became breathable

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