If the world (Earth) were to become so polluted that the surface would become uninhabitable, how long would it take to become as unpolluted as it was before humans?

By pollution I mainly mean chemicals/elements that would normally not belong in the atmosphere or which have abnormally increased amounts of that particular chemical/element. Plastics and/or harmful metals I would also count as pollution.

(I'm mainly wondering about pollution in the oceans. If the information could be altered by the gravity of a planet then assume that it's a similar gravity to Mars.)

  • $\begingroup$ Hi SlothsAndMe, welcome to Worldbuilding! You may get better answers if you define what pollution is to you; CO2 will be very different from plastic $\endgroup$
    – Dubukay
    Dec 30 '18 at 2:25
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    $\begingroup$ Alright I tried to fix that hope it's a little better now :D $\endgroup$ Dec 30 '18 at 2:31
  • $\begingroup$ I added chemistry and poisons as tags (and removed time, which is meant for discussing aspects of time, not for time passing) but I'm unhappy with poisons. I would prefer "toxicity" or "toxins" but it doesn't exist. Poisons is the closest, and according to a Meta discussion, might be intended to cover toxicity. $\endgroup$ Dec 30 '18 at 3:11
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    $\begingroup$ This is too vague. What does it mean to be uninhabitable? the whole planet? Caves? Underwater? How much pollution are we talking about? Without a sensible (and definable) starting point, how can we answer the question? $\endgroup$ Dec 30 '18 at 6:34
  • $\begingroup$ I've already accepted an answer so I don't see an issue anymore with how vague it is and I really did try to explain as well as I can. I also said that the surface is the location becoming uninhabitable. I also stated earth which I assume would cover the location and the amount of pollution is however much it would take to cause the planet to be uninhabitable. As im still going through education I wouldn't know how much that would take. $\endgroup$ Dec 30 '18 at 7:27

Any length of time

The pollution can essentially be tailored to fit any length of time, from microseconds to "longer than the existence of the universe" using the half-life of radioactive isotopes. https://en.wikipedia.org/wiki/List_of_radioactive_isotopes_by_half-life

Assuming the pollution is the result of a specific industry on the planet, it can be lawfully evacuated by order of the Intergalactic Safety Regulation Committee. In other words, you don't actually have to poison the whole planet to black goo to force everyone to leave, you just need environmental regulation and aggressive enforcement of the evacuation.

If you need an exact transition date when colonists can reclaim the planet, have the Intergalactic Safety Regulation Committee designate the planet as "uninhabitable" until the radiation drops to a certain level – which is mathematically calculable. Flora and fauna will thrive long before the pollution has "disappeared" completely.

Disappear, or just drop below toxic levels?

The toxins may never disappear completely without a trace.

Re-colonists could return to find a "clean" planet, or a "less-toxic" planet, or a "still-very-toxic-but-we-made-a-deal-with-the-environmentalists-to-be-great-again" planet. It's up to you.

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    $\begingroup$ Well you see the civilization causes a catastrophy and go to hide in a underworld cave system until their mathmeticians figure the planet is safe enough to go live in again without issues. But I suppose that government intervention would be a feasable enough explaination for why they go hide I suppose. $\endgroup$ Dec 30 '18 at 5:40
  • $\begingroup$ I'm pretty sure that direct gamma pollution is gone really quickly. $\endgroup$
    – Joshua
    Jan 25 '19 at 23:33

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