Imagine we find a habitable planet. It’s been (geologically) recently sterilised by a gamma ray burst, so there are no nasty microbes and the oceans are reverting to a primordial state. There is no oxygen in the atmosphere - it’s long been used up oxidising rocks. We’ve arrived in orbit via hyperdrive and …
Suppose we seed the oceans with algae and stromatolites (and what else?). How long will it take for a relatively breathable atmosphere to develop? There are no predators (yet) so both species should do very well very quickly.
Then what? Can we plant terrestrial flora before the atmosphere is breathable by humans?
Good question. I’d bet it would depend on the available resources, such as how much of the surface was covered with water. Another factor, somewhat determined by the thickness of the existing atmosphere, would be warmth. Given a thick enough and warm enough atmosphere with some Oxygen, Nitrogen and CO2, I should think there are a lot of plants that would grow just fine in an environment insufficient to support Human Life.
But we could certainly build larged domed structures in which we start our initial gardens and live until the atmosphere is built up enough to move out of them.
How exactly is the oxygen bound up? I’m not sure what we’ve got just laying around that frees bound oxygen from rust easily. You’d have to wait until the entire oxidized mineral base breaks down itself. Second, that atmosphere couldn’t possible have had enough oxygen to be habitable unless there’s something present which absolutely devours oxygen.
Basically, it’s not going to happen in anything like a timescale in which we can plan. You’d be lookign at millions of years to free the oxygen. On earth, we needed cyanobacteria working for something like a billion-and-a-half-years to do this.
The planet’s been sterilised by a GRB. Maybe there were flying monkeys with chlorophyll, maybe life never developed; there’s nothing organic there now.
Why not? Algae doesn’t need oxygen. It processes the CO2 in the air.
Yeah, but not quickly. Are we talking some genetically-engineered super-algae that could cover all watery surfaces on the planet in a few months and process CO[sub]2[/sub] with double or triple efficiency? Even then, we’re talking hundreds of years before humans can walk around without supplementary oxygen, even in the lowlands.
Not necessarily true. If there was life recently (destroyed by a nearby gamma ray burst) there will be oxygen. But it’s likely bound up in CO[sub]2[/sub] and other less-than-ideal forms for our use. If there’s sufficient carbon dioxide then plants should be being able to break the O[sub]2[/sub] from the C (such as it were).
Even were that the case, though, it would take a hell of a long time to acheive homeostasis again. The main goal would be to get algae photosynthesizing in the shallow oceans PDQ. Fast, grows fast, and will spread quickly throughout the oceans rather than say, a patch of trees or something that will stay in one place.
No, he said it was all bound up in the rock. And with the planet sterilized, there’s going to be precious little even for algae. They dont’ spread that fast. And no, we can’t “pin the period down” because you’ve left out all the really important details. Hell, I’m not even sure if any organism living right now even could handle the job you’ve put down in mere eons, instead of hundreds of eons. You’re basically rebuilding the entire planetary atmosphere.
Because it takes a very long time. And no, algae doesn’t spread that fast, because it has no nutrients. They’re gone with the sterilization. It takes a hell fo alot mroe than sunlgiht and CO2 to make more algae.
For comparison, we’re currently trying and failing to do the same thing on Earth, on a much smaller scale. The problem of extracting oxygen from atmospheric carbon dioxide is exactly the problem of sequestering the carbon from it. Here on Earth, we’ve got a small fraction of a percent of an atmosphere that’s carbon dioxide, and we don’t have any workable plan for sequestering it. You’re positing a world where we have at least 23% of an atmosphere that’s carbon dioxide (else we wouldn’t be able to make enough oxygen out of it), and we’d need to sequester all of that.
Another problem: If that planet has that much CO[sub]2[/sub] at the start, then it’s got one heck of a greenhouse effect. Take that away, and the planet will cool significantly. Chances are, it’s either too hot for the algae before we start terraforming, or it’s too cool for us after we finish.
I don’t believe there is any event that could sterilise an entire planet without also stripping the atmosphere or reducing the planet to rubble and scattering the pieces. Gamma ray bursts only last a few seconds, they could conceivably kill all life on the side facing the gamma ray when it hit but not the whole planet.
IMO a more interesting and likely question is if we found a planet equivalent to our Proterozoic age that had only anaerobic organisms and no oxygen in the atmosphere but plenty of CO2, water, nitrogen, then how quickly could we create a breathable atmosphere?
I don"t believe a GRB could kill deep ocean life, either. Consider the anaerobic vent colonies, sitting there with a humongous fall of protein from the sterilized upper layer. Somethings gonna happen. Maybe nothing that will release O2, however.