So, one of my main settings involves humanity colonizing an Earth-like planet. The planet has all the abiotic features needed to support mankind (oxygen-nitrogen atmosphere, magnetic field, 70% surface oceans, plate tectonics, a moon) and once had its own biosphere, which was recently wiped out in a tragic extinction event (luckily, this means that we have a source of alien fossil fuels). This is mostly because I’m not quite the best with speculative biology, and that my setting focuses more on the societal and technological aspects of humans starting anew on a planet near-identical to their own.

When humanity discovers this planet, they begin sending probes built to re-populate the planet with Earth’s native flora and fauna. How long would this process take? Is there a way that this process could be sped up, like GE’d organisms that reproduce faster?


For more information on the planet and it’s star system, the star system is very similar to our own.

  • The sun is a singular G-type star.
  • The planet has a rocky moon that causes moderate tides.
  • The planet’s rotation period and orbital period are like that of Earth’s, and will lead to a calendar that is equally similar.
  • The planet is smaller than Earth. However, the size difference between the two planets is so negligible that they might as well be the same size, like Venus and Earth.
  • The planet’s composition is very alike to Earth’s, to the point where many of the natural resources found on Earth can be found here.
  • The planet’s starward neighbor is a Mars-like analogue. I plan on the colonists regressing in technology after landing, and re-developing into a post-modern age, including just starting to colonize this planet.
  • The planet also has a large Jupiter-like gas giant which deflects meteors from the planet.
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    $\begingroup$ One major problem. Without its own native photosynthetic organisms (at least micro organisms) the world wont have any free oxygen in its atmosphere, well almost none anyway. This is because oxygen is highly reactive and binds readily with multiple other elements. Iron and other metals are excellent examples for instance but it readily combines with other elements as well. The Earth only has high levels of oxygen in it atmosphere because it is constantly being replenished by photosynthesis. $\endgroup$
    – Mon
    Jan 10, 2023 at 7:28
  • $\begingroup$ So you either need; A) primitive single cell photosynthetic organisms to be present on the planet or B) your Terraforming project is delayed while you raise oxygen levels to something approaching breathable levels. The good news though that this 'should' be a relatively easy process i.e you simply seed the planet's surface (especially it's oceans) with algae. But to get to modern level oxygen levels is still going to take you an unknown amount of time. Centuries at least, probably thousands of years. $\endgroup$
    – Mon
    Jan 10, 2023 at 7:32
  • $\begingroup$ @mon it is not stable over geological timescales, but I’d you vanished the earth’s biosphere right now it’ll take on the order of 1-10 million years to remove all the free oxygen. $\endgroup$ Jan 10, 2023 at 7:40
  • $\begingroup$ Is it archipelagos, a single continent or mixed? What proportion of land counts as success? Considering that some species don't reach sexual maturity for over a century (Greenland shark, some trees), what number of species count as success? What about complexity of ecosystems - or will just some niches filled count? Could you supply more details of your planet and of the criteria. $\endgroup$ Jan 10, 2023 at 8:01
  • $\begingroup$ @Starfish Prime. Which then requires some kind of plausible explanation for why ALL photosynthetic organisms on the planet down to algae suddenly went extinct! Earth has never experienced an extinction event that caused everything but its microbiome to disappear during it's entire history. $\endgroup$
    – Mon
    Jan 10, 2023 at 8:30

1 Answer 1


**It depends how much biodiversity you want.

You should start with basic plants. Introduce green algae and Cyanobacteria to the waters first, followed by kelp and sea-grass. Mosses and lichens should be brought onto the land, followed by grasses and various essential fungi. This will take relatively little time as all these plants are slow growing; maybe ten years.

Then, bring the basic animals; soil nematodes, benthic worms, earthworms, woodlice, mayflies, dragonflies, beetles and ants. Don’t forget ocean invertebrates such as krill, various crabs, starfish, sea cucumbers, water snails and nudibranchs. Getting these critters established will be easier; just scatter them here and there and they will spread out themselves in just a year or two.

Now add more complex life forms. Trees should now be yintroduced; to avoid hassle over what species, let’s just go with a single type for each biome: some kind of palm tree for the tropics, spruce trees for the arctic regions, and oak trees for the temperate zones. Planting these may take some time; it will take at least twenty years for these new forests to reach full size.

What large animals you want depends largely on taste, but you’ll want to avoid dangerous animals. Bring dolphins to keep down the marine fish population and just small carpet sharks for eating benthic critters. Bring in insectivorous birds to keep down the insects, and ideally some form of tropical bird to disperse the palm fruits’ seeds. You might not want rodents in case they damage crops, but hey, you’ve probably been farming in greenhouses at this point, so why stop? So bring rodents as prey for the predators you’ll also need to hunt more essential fauna. These (the predators) include hawks and owls to keep down freshwater fish and small birds. Just to be sure the rodent numbers stay down, introduce small predators such as weasels, ferrets and mongooses. Rabbits, hares, small monkeys and bobcats are not essential but will fit into this basic ecology I reckon, so add them if you want. All these animals should be given maybe another ten years to get established and to find some kind of ecological balance.

So, adding all this up, you’re looking at about 10 years before the oxygen levels are maintained, two years before you can have a crab supper, twenty years before you’ve got proper forests, and another ten years before there is birdsong in the air. All in all, it should take about 42 years to terraform this world.

If you think this is a long time, then remember your colonists are lucky to have found a planet that is basically a second Earth bar the life forms, and which comes pre-stocked with oxygen and fossil fuels so you can make all the same mistakes of global warming that your ancestors made. Hooray!

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    $\begingroup$ This somehow feels like an overly optimistic amount of time :thinking: $\endgroup$
    – Mr47
    Jan 10, 2023 at 15:47
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    $\begingroup$ I'm a bit less optimistic. For the first decades or maybe centuries the ecosystem would be a formidable mess: some species will fare better than others, drive others into extinction by predation or competition, then go extinct themselves or at least decline because they no longer have food. Achieving a balance will take time. Think of islands where non-native species have been introduced. $\endgroup$
    – Cloudberry
    Jan 10, 2023 at 18:02
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    $\begingroup$ So is 42 the answer to the ultimate question of life? $\endgroup$
    – gmauch
    Jan 10, 2023 at 20:22
  • $\begingroup$ @Mr47 yes it is somewhat of a a "maximum optimism"-based calculation, but given that the terraformers are an interstellar civilization, the resources to intervene if stuff goes out of balance etc. is assumed to be available. As well as frequent flights over the entire planet to spread seeds/eggs / etc.. But IF those requirements are met it's not too unrealistic imho. The resulting ecosystem likely won't be stable without intervention for a much longer time, but that's not what OP asked for $\endgroup$
    – Hobbamok
    May 5, 2023 at 8:43

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