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What changes/additions/deletions, large or small, minimum handwavium allowed, would be needed to make suspected water covered exo-planets such as Gliese 1214 b, Kepler-22b, Kepler-62e, and Kepler-62f, habitable to life?

Would it help if they were closer/further from their sun? Would cometary bombardment add favorable qualities? Would bacteria/algae be useful? Does it's rocky core need to be changed as well? Are there elements that are missing altogether that could be useful?

EDIT: 2 things

  1. What do I mean by habitable?: That there be complex native wildlife there, at least the equivalent of fish, whales, sharks, squids. Also I'd like to think that visiting humans wouldn't automatically die by going to the surface. For example, it'd be nice if they didn't freeze or boil or be poisoned to death by toxicity of some kind, or blasted by radiation, even if they have to wear a suit and breathing apparatus. I hope that helps narrow things. If not, let me know.

  2. Some info I found suggests lots of differing trains of thought on the matter...

https://www.scientificamerican.com/article/are-water-worlds-habitable/

…wet worlds have sparked a lively debate about how much water is too much. …(the)“carbon-silicate cycle” is a balancing act that many scientists argue is crucial for long-term habitability. But on water worlds that cycle may be impossible. …worlds awash with so much water present other hurdles for life. That ice layer, for instance, makes it more difficult for organisms to scrape nutrients like phosphorous (the backbone of DNA) from the rock, potentially preventing life from emerging in the first place. “You have a temperate planet and if you and I landed on it, maybe we wouldn’t boil or freeze, and we’d have lots of water—but there just wouldn’t be enough nutrients to actually kick-start life,”…

https://sites.coloradocollege.edu/pc120ml/2013/10/23/an-investigation-of-gliese-1214bs-habitability/

The thick atmosphere exerts an incredible amount of pressure on Gliese 1214b’s surface. In addition, the surface temperature is estimated at a range of 393-555 K. The calculations below confirm Gliese 1214b’s extremely high surface temperatures. At these high temperatures and high pressures, water cannot exist, on the surface, as a liquid. Therefore life, similar to life on Earth, cannot exist on Gliese 1214b’s surface. But, life may exist in its watery core, much like the possibility that life exists in the subsurface ocean, of Jupiter’s moon, Europa. Currently, scientists speculate the presence of “hot ice”, “superfluid water” and “plasma water” on its surface. Life, like life on Earth, cannot exist or evolve in these extreme phases of water. Such a possibility cannot be ruled out because some sort of thermophile may be able to withstand the grueling temperatures and high pressures on its surface, or in the subsurface ocean. Though this does not seem possible because at these high temperatures complex chemistry, essential to life, breaks down. Without the formation of chemical bonds life, of any kind, simply cannot form. This does not completely eliminate the possibility of life. Below the surface, temperatures may be lower therefore liquid water could exist.

https://www.space.com/23028-super-earth-water-atmosphere-alien-planet.html

Though water is often considered a necessary ingredient for life by scientists, Narita doesn't think that the super-Earth will be promising due to its close orbit, which lies within the star's habitable zone, the region where liquid water can exist.

EDIT: I found some answer in the "Origin of life on a waterworld" question. Thanks.

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  • $\begingroup$ What about those worlds you listed make them uninhabitable? We haven't visited or directly imaged those worlds yet, who's to say they aren't already habitable? I think your question lacks focus. We can't make assumptions about those planets on your behalf. $\endgroup$
    – BMF
    Apr 7, 2021 at 14:55
  • $\begingroup$ water worlds (as a type of earthlike planet) are already believed habitable to life. why wouldn't they be? they're just like earth but without continents and very big oceans, its as habitable as a scaled up version of the pacific ocean. $\endgroup$
    – zackit
    Apr 7, 2021 at 15:07
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    $\begingroup$ @zackit depends on what the OP means by "habitable". There's limited scope for photosynthetic things and the food webs that depend upon them on deep-ocean water worlds, for example; difficult to circulate the required nutrients all the way up through the water column. Hydrothermal vents should be just fine, though. $\endgroup$
    – Starfish Prime
    Apr 7, 2021 at 15:23
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    $\begingroup$ If you limited your question to one planet and gave a list of local conditions that were a barrier to life, then we could give you an answer. We only have superficial data for these places, so we can't make a realistic analysis. $\endgroup$
    – DWKraus
    Apr 7, 2021 at 16:18
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    $\begingroup$ Need a clearer definition of "habitable." Habitable to humans and our pet dogs? Habitable to anaerobic early life? Different answers for different habitats. If you want human habitability, one of your big problems is oxygen for the atmosphere -- our is a byproduct of a couple billion years of life. $\endgroup$
    – user535733
    Apr 7, 2021 at 16:36

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The planet will need to have a strong magnetic field, a tolerable temperature and pressure, and an chemical composition that supports life. There needs to be carbon dioxide, oxygen, nitrogen, etc. in the atmosphere and water, so that life can form there. And an energy source, typically a sun or two. A planet covered in a global ocean of liquid water can support life, even if that ocean’s top kilometre is frozen over. Scientists believe that the Jovian moon Europa, which has more water than Earth, despite being smaller, has life in its liquid mantle, beneath its crust of ice.

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  • $\begingroup$ Unless I misunderstood, I've been reading that Gliese 1214 b and at least one or two of the Keplers have oceans of liquid water and maybe even atmospheres of supercritical gases(?) Possible to exist? Possible to sustain life with those conditions? What if Titan were closer to the sun? Thoughts? $\endgroup$
    – Len
    Apr 23, 2021 at 0:54
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    $\begingroup$ @Len Water’s critical point is 374 Celsius and 218 atm. In theory, life could exist under such temperatures and pressures, but most likely not with the same biochemistry as the life we know. In fact, if we found life swimming in oceans of supercritical water, we might not at first recognize it as life. $\endgroup$
    – TysonDennis
    Apr 23, 2021 at 0:58
  • $\begingroup$ dont say that. That's the whole story right there. 😒 $\endgroup$
    – Len
    Apr 23, 2021 at 5:19

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