# How long to settle a virgin planet? **URL:** \ **Category:** Great Debates\ **Created:** [January 16, 2012, 5:23pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706 "2012-01-16T17:23:59Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [January 16, 2012, 5:23pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/1 "2012-01-16T17:23:59Z")
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? ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [January 16, 2012, 5:49pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/2 "2012-01-16T17:49:07Z")
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. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [January 16, 2012, 6:03pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/3 "2012-01-16T18:03:07Z")
> [@Chimera](#): > > 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. Assume no atmospheric oxygen, at least initially. Assume also 70% water coverage, just like Earth. And it’s not an ice age. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [January 16, 2012, 7:38pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/4 "2012-01-16T19:38:40Z")
> [@Quartz](#): > > Assume no atmospheric oxygen, at least initially. Assume also 70% water coverage, just like Earth. And it’s not an ice age. 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. > **[Geological history of oxygen](https://en.wikipedia.org/wiki/Geological_history_of_oxygen)** > > Although oxygen is the most abundant element in Earth's crust, due to its high reactivity it mostly exists in compound (oxide) forms such as water, carbon dioxide, iron oxides and silicates. Before photosynthesis evolved, Earth's atmosphere had no free diatomic elemental oxygen (O2). Small quantities of oxygen were released by geological and biological processes, but did not build up in the reducing atmosphere due to reactions with then-abundant reducing gases such as atmospheric methane an Ox... > **[Cyanobacteria](https://en.wikipedia.org/wiki/Cyanobacteria)** > > As of 2014\[update\] the taxonomy was under revision > Cyanobacteria (/saɪˌænoʊbækˈtɪəriə/ sy-AN-oh-bak-TEER-ee-ə) are a group of autotrophic gram-negative bacteria of the phylum Cyanobacteriota that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" (from Ancient Greek κύανος (kúanos) 'blue') refers to their bluish green (cyan) color, which forms the basis of cyanobacteria's informal common name, blue-green algae.\[note 2\] > Cyanobacteria are probably the most num... ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [January 16, 2012, 8:20pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/5 "2012-01-16T20:20:28Z")
> [@smiling\_bandit](#): > > 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. 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. > [@](#): > > Basically, it’s not going to happen in anything like a timescale in which we can plan. Why not? Algae doesn’t need oxygen. It processes the CO2 in the air. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [January 16, 2012, 8:27pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/6 "2012-01-16T20:27:00Z")
> [@Quartz](#): > > 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. ---
**Author:** ![Jonathan\_Chance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jonathan_chance/32/701_2.png) [@Jonathan\_Chance](https://boards.straightdope.com/u/Jonathan_Chance)\ **Post date:** [January 16, 2012, 8:32pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/7 "2012-01-16T20:32:04Z")
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. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [January 16, 2012, 8:40pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/8 "2012-01-16T20:40:59Z")
> [@Bryan\_Ekers](#): > > 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. Hundreds of years? Remember that the algae have no predators and the water is nutrient-rich. They’re going to multiply very rapidly. But anyway, so what if it takes hundreds of years? Humanity’s going to be there for the long term. Could you pin the period down more precisely? ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [January 16, 2012, 8:51pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/9 "2012-01-16T20:51:03Z")
More than a dozen, less than 20,000. It’s the best I can do. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [January 17, 2012, 3:30am UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/10 "2012-01-17T03:30:55Z")
> [@Quartz](#): > > Hundreds of years? Remember that the algae have no predators and the water is nutrient-rich. They’re going to multiply very rapidly. > > But anyway, so what if it takes hundreds of years? Humanity’s going to be there for the long term. Could you pin the period down more precisely? 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. > [@](#): > > Why not? Algae doesn’t need oxygen. It processes the CO2 in the air. 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. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 17, 2012, 4:18am UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/11 "2012-01-17T04:18:19Z")
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. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [January 17, 2012, 5:15am UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/12 "2012-01-17T05:15:26Z")
> [@Quartz](#): > > 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. 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? ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 18, 2012, 11:58am UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/13 "2012-01-18T11:58:30Z")
I’d go with at least tens of millions of years, if not hundreds. ---
**Author:** ![robinson](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@robinson](https://boards.straightdope.com/u/robinson)\ **Post date:** [January 20, 2012, 6:24pm UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/14 "2012-01-20T18:24:31Z")
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. ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [January 21, 2012, 12:06am UTC](https://boards.straightdope.com/t/how-long-to-settle-a-virgin-planet/609706/15 "2012-01-21T00:06:02Z")
> [@smiling\_bandit](#): > > 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. Sterilization isn’t going to remove dissolved minerals and the like.