My colonists have been terraforming a planet for centuries. They chose this exo-planet for its many earth-like qualities (size, gravity, Goldilocks zone, volcanos, similar sun). However, it is like the Earth of 400 million-ish years ago. The atmosphere has lots of nitrogen but not much oxygen. Also, a great deal of water is tied up in glaciers though there is some very basic plant life near the equator. The oceans have lots of critters but it is a lot less ocean than Earth. There are “red beds” indicating that all the minerals that could have reacted with free oxygen have already done so.

They have been using solar collectors and mirrors to melt the glaciers. This puts a little oxygen into the atmosphere by splitting the H’s and O’s. Mass plantings of genetically modified organisms have also increased the oxygen. The gardener in me wants there to be legumes to fix the nitrogen in the soil for future use by farmers.

The people live in domes on the moons of this planet, a space station, and domes on the planet surface. They really want to spread out and use this beautiful planet.

My question: Is it plausible that they could get the oxygen level up to 21% (like Earth) in a few centuries. Will they be able to stop it at the right number?

These two articles were helpful in getting at how Earth’s atmosphere developed but so much of the timeline described involves waiting for specific organisms to evolve. The colonists have Earth plants and a talent for GM which should help a great deal.

Evolution Of The Atmosphere: Composition, Structure And Energy http://www.globalchange.umich.edu/globalchange1/current/lectures/Perry_Samson_lectures/evolution_atm/#

The Mystery of Earth’s Oxygen http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html?_r=1&&module=ArrowsNav&contentCollection=Science&action=keypress&region=FixedLeft&pgtype=article

  • $\begingroup$ If there are so many glaciers then the average temperature is probably lower than Earth's so the colonist would probably want to bring it up a bit too right? $\endgroup$
    – ventsyv
    Apr 18, 2017 at 17:38
  • $\begingroup$ @ventsyv: Why? Much of the Earth - the tropics, basically - is too warm for comfort. $\endgroup$
    – jamesqf
    Apr 18, 2017 at 18:10

2 Answers 2


Photosynthetic algae

One of the first great extinction events of our world was the mass oxidation of the atmosphere by cyanobacteria (among other organisms). From the Wikipedia article: "For example, at today's rates of photosynthesis (which are much greater than those in the land-plant-free Precambrian), modern atmospheric O2 levels could be produced in around 2,000 years."

What this means is, in 2,000 years, with no effort other than adding an Earth-like amount of plants, you could get the atmosphere you want. But how would we do better? Enter photosynthetic algae. On our world, algae is kept in check by filter-feeders (shellfish, for instance) and a lack of free nutrients. On your world, presumably there are no filter-feeders. So, dump acres of algae into the newly-forming oceans. A lot of accidental algae blooms are caused by fertilizer runoff into waterways, so add fertilizer. This would vastly reduce the time it takes to convert CO2 into O2.

Figure out a way to clean this up after the fact, and you're golden. Either add filter feeders, or make them dependent on the fertilizer would be my strategies.

Another possibility is base-six DNA. As long as you continue to supply the extra base pair in your fertilizer dumps, the genetically modified algae will survive. Stop supplying it and it dies almost immediately. (Thanks to Draco18s for the base-six DNA idea!)

  • $\begingroup$ When to stop actively terraforming and stabilizing the atmosphere is a plot point in my story. I need to look more into the "clean up" as you put it. $\endgroup$
    – Mazel
    Apr 18, 2017 at 18:02
  • 6
    $\begingroup$ Cleanup idea: base-six DNA. As long as you continue to supply the extra base pair in your fertilizer dumps, the genetically modified algae will survive. Stop supplying it and it dies almost immediately. $\endgroup$ Apr 18, 2017 at 18:11
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    $\begingroup$ "Figure out a way to clean this up after the fact, and you're golden." - no CO2 no plants. So have proper amount of CO2 to start with and you are golden. $\endgroup$
    – MolbOrg
    Apr 19, 2017 at 22:20
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    $\begingroup$ I mentioned volcanos. There is some CO2. $\endgroup$
    – Mazel
    Apr 20, 2017 at 15:21

Yes. If they pump up CO2 into the atmosphere in sufficient quantities, the global average temperature will raise and the glaciers will melt. The resulting wetter, warmer, C02 rich climate will be excellent for plants.

A quick search online found this paper: http://rstb.royalsocietypublishing.org/content/314/1167/523

GMOs will have much higher rate of spread, in a few hundred years they could easily cover the whole planet in woods thus sucking up the C02 and replacing it with oxygen.

  • $\begingroup$ The problem with this is that oxygen has a global cooling effect. As soon as the oxygen level gets high enough you'll trigger an ice age and all those plants will start to die. $\endgroup$ Apr 18, 2017 at 21:38
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    $\begingroup$ @TomO'Daighre Not necessarily. When you suck up the CO2 the temperature will fall, but not to the level before terraforming began because the additional water vapor from the ice that melted will help against that. $\endgroup$
    – ventsyv
    Apr 18, 2017 at 21:45

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