Oxygen is such a beautiful double edged sword. We need it to live, but we need complex biochemical pathways to be able to survive it. If our ancestors hadn't evolved their way through this event we wouldn't be alive, but if the event had never happened we wouldn't be multicellular intelligent life forms. And now we need it to live.
And within a pretty tight range, too. I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously; if less than 15%, they wouldn't be able to burn at all.
> I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously
Oxygen reached 35% during the Carboniferous. This lead to lifeforms taking advantage (e.g. giant invertebrates outside the seas) as well as rainforest wildfires as the oxygen levels significantly increased flammability of flammable materials (most of our coal dates back to these days, where rainforests would grow quickly, burn down to 10~20% charcoal by volume, and that charcoal would fossilise over time).
Somewhat oddly, very few things are hypergolic with oxygen, even LOX (which is as full of oxygen as you can get) or 100% oxygen atmosphere. Fuel will readily ignite, but it needs an ignition source of some sort.
This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water.
> This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water.
Speaking of things that 'splode, there's a lovely article that makes the rounds here every so often by Dr. Derek Lowe on the onomatopoeically named FOOF (dioxygen diflouride)[1], one of his "Things I won't work with."[2]
I guess, I was using "oxygen" as a shortcut for "O2" which does make me technically wrong.
Though ozone is as toxic as fluorine and tend to spontaneously explode, according to Ignition! it can be made safer by mixing it with LOX but to reach safe use levels you apparently need to get down to ~25% O3, at which point it's just a harder to handle LOX.
It seems (I didn't remember this passage) folks also tried out mixing ozone with fluoride, which strikes me as a very Cave Johnson idea.
It's not that extreme. Things don't catch fire spontaneously even when the atmosphere is 100% oxygen (you still need an activation energy) but a fire that starts in this conditions is incredibility fast: some things even becomes explosive because of that. See the Apollo 1 accident [1].
Not with oxygen but flourine (and some of it's compounds) will actually cause spontaneous combustion in a wide range of things such as burnt coal and asbestos.
In "Oxygen: the molecule that made the world"[1], Nick Lane also mentions the theory that these cyanobacteria are the reason we have liquid water on earth, while mars (for example) doesn't.
It goes like this: early earth was subjected to solar radiations which hit our liquid water, splitting H2O into separate oxygen and hydrogen elements. The very light hydrogen atoms (as ions, or maybe H2?) were escaping into space while the oxygen was trapped by oxydizing rocks.
With the rise of cyanobacteria produced O2, the rocks became fully oxydized and O2 started to build up in the air: the split hydrogen would be more likely to recombine with atmospheric O2, keeping them on earth, and the ozone (O3) layer started to shield the water from these radiations in the first place, thus stopping the process and safeguarding our oceans.
[1] https://www.amazon.com/dp/0198607830 (very cool read mixing early earth history, the rise of life, geology, biochemistry and phylogenetics + Dr Lane is an excellent writer. Published in 2002, he has many more good updated articles about it.)
Cyanobacteria is the most influential organism in the history of the planet. Nothing comes even close (arguably including humans). Nearly all of the energy processed in living organisms can be traced back to cyanobacteria (either via photosynthesis, or via consuming products of photosynthesis, or products of consuming products of ...). This extends to modern human energy usage via fossil fuels.
Humans make a big deal out of 0.01% CO2, a relatively inert gas.
Cyanobacteria turned 20% of the atmosphere into very reactive O2.
I like to point that out when people say that we are destroying our planet. Our planet will be fine with or without us, we are just hoping that it will be with us.
And cyanobacteria is a small deal compared to the formation of earth or supernovas. Which are absolutely nothing compared to the big bang or the heat death of the universe.
Humans should definitely make a big deal about their own survival.
It depends on how you define 'our planet' though, no? There are things you could do to this planet that would wipe out most forms of life on it and at present we've been seeing decreasing populations of insects, animal species, etc. The planet will certainly still be here but it's a pretty big bummer if we manage to knock out half the biological diversity or more on our way out. Without biological diversity and feedback loops our planet is just soil and water.
i've lost an hour or so recently reading about a more recent event after which there no longer were palm trees in the arctic: https://en.wikipedia.org/wiki/Azolla_event
> A chronology of oxygen accumulation suggests that free oxygen was first produced by prokaryotic and then later eukaryotic organisms in the ocean that carried out photosynthesis more efficiently, producing oxygen as a waste product
So oxygen is a sign of life. Can we measure oxygen's spectral line from any exoplanets? Would enough O2 suggest our kind of life is more likely there? If we could survey exoplanet atmospheres in our neighborhood for oxygen would that tell us anything about the distribution of life?
Oxygen spectral lines are mostly distinct from the non-life planet ones, so I would be greatly surprised if we couldn't measure it and if astronomers didn't do that for each planet they observed by transition.
Free oxygen is a pretty good sign of life and if we were to see it in other planets' atmospheres that would be a good indication that life was there. But on the other hand, there was life on Earth for a long period of time before photosynthesis was evolved, then there was a long period of time before large amounts accumulated in the atmosphere. So while this test is relatively easy to apply across a large number of planets it would tend to give a lot of false negatives.
It seems plausible that on many planets you have life evolving but because it's slow to develop photosynthesis the solar wind strips away all the hydrogen before the production of oxygen creates a protective ozone layer. Maybe that even happened on Mars, though with the lack of magnetic field there and shallow gravity well it was going to lose its hydrogen eventually even with an ozone layer.
Oxygen tests are definitely a part of exoplanet searches.
Looks like determining abiotic oxygen situations in the "goldilocks zone" versus potentially biotic or life-supporting is an ongoing field of exoplanetary research:
