> 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

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.

This is definitely a useful way to frame this for some purposes. For other purposes it’s important to understand that our current good-for-humans-atmosphere is a happy, ridiculously complex accident, and potentially a fragile one.

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.

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.

Regardless, prokaryotes lacked the ability to tolerate the oxygen that they (as cyanobacteria) produced.

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.

Metaphor is a common and delightful way to use language - you should try it sometime. It helps avoid the delusion that language has some inherent amount of rigor or correctness. Or that grammatical rules actually exist unchanging rather than being rules written by people making them up from the types of language and speaker that they approve of.

Metaphors can be wrong. This one, for example, is.

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)

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.

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

There's an inferred "to us"

Precisely — whatever ‘us’ is inferred to be, we’d have to be able to breathe whatever atmosphere we are immersed in. There’s selection bias at work here.

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.

> 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.

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

The calculations currently work out that the dumb luck is so incredibly lucky that it doesn't seem feasible to have happened in the observable universe due to the number of zeros involved.

But the whole point of the anthropic argument for anything (oxygen, goldilocks earth, fine tuning) is that it doesn't matter how slim the odds are. We cannot observe a universe where the lucky thing doesn't happen because we can't exist in such universe.

This is solving the problem by adding infinity more universes, which actually lets you solve anything :)

Even our own universe could be vastly larger than the observable portion.

The universe is probably a whole lot larger than the observable universe.

Is it 10^100* bigger?

If inflation occurred at an early time, it could indeed be vastly larger.

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

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

Kudos.

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.

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

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

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

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

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

> 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.

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"

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.