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Here's the setting:

Advanced human civilizations of an ancient time destroyed the ozone layer of the planet. They managed to create an self-sustaining artificial layer which would function exactly as the original, however (through miscalculations maybe, I haven't figured that out yet) it would not only absorb harmful UV lights but also a big portion of visible light.

But not so long after the planet still became a wreck and humans almost killed each other to extinction (basically what happens to us in a not-so-far future?). Some found a way to survive until the planet became stable again (not sure how much time exactly but probably in the order of thousands/millions of years?) maybe by putting themselves to cryogenic sleep or something to wake up when the planet becomes livable again (still haven't figured that out, not very relevant).

Point being, during the time the planet stabilized and life and nature reclaimed their territory without human intervention, the artificial layer was still active, so everywhere everything was very dim.

Question details:

What is going to be directly affected by having less sunlight (specific types of species for example)? Flora dependent on photosynthesis will still get some light, but is it going to be enough (especially to sustain ecosystems built around them)?

What are some options/alternatives for this light-dependent life to evolve into/switch to?

More details:

I read all of the questions pertaining to worlds with little to no light, but they were either about total darkness, or very short darkness periods, or about how humans cope, or about having specific climates that are not very Earth-like, etc.

Nevertheless, I saw stuff like:

  • Bioluminescence (I'd love to have a lot of it)
  • Different plants colors, if plants start absorbing all light, or different light
  • Echolocation
  • Chemosynthesis or similar system that doesn't work with light

Things to keep in mind:

  • It's an Earth-like planet, 1.4 times the mass of Earth
  • In a double planet system with another Earth-like planet (about the same mass as Earth) (this could cause tidal forces)

EDIT: I came to realize I don't have enough information about the environment to try thinking about what grows in it for now. I'll open a new question about that and come back to this topic later (with a more specific question -- it's my first one and I made so many mistakes). I'd still appreciate your thoughts/ideas though, and thanks to anyone who took the time to answer, it helped!

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    $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    May 19 at 14:26
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    $\begingroup$ There are plenty of examples of plant life in limited light environments. On the forest floor, in caves, under the sea... $\endgroup$ May 19 at 14:28
  • $\begingroup$ Does this artificial layer traps infrared, creating greenhouse effect and possibly maintaining comfortable temperature, or dimming effect just reflects light back into space, creating an ice age? $\endgroup$
    – Alexander
    May 19 at 15:42
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    $\begingroup$ @BryanMcClure I just realized it seems you have misunderstood... the layer cuts off MOST light, not all. so it's not total darkness, I guess something like sunset. A new ozone layer didn't come to be, the artificial layer never stopped working. (all this is in the original post) destruction of the world isn't because of the ozone getting destroyed either, I doubt that would be even possible... but a whole lot of other factors. As I said I intentionally left out a lot of unnecessary details not relevant to the point $\endgroup$
    – Lulullia
    May 19 at 16:51
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    $\begingroup$ @Lulullia, yes, with a very little handwavium you can say that despite low level of visible light, the planet gets more infrared which keeps the temperature at desirable level. $\endgroup$
    – Alexander
    May 19 at 18:14

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It would depend on how much less light.

Because the major issue is the energy balance.

  • If there is less sunlight this implies less energy.
  • Less energy means lower average temperature.
  • Lower average temperature means more snow and ice, which have higher albedo which can further drop temperature.
  • Lower average temperature means less evaporation, which means less rain.
  • More likely to have spurious frosts that can devastate crops.

There are other affects. The longer this goes on the more changes can pile up. Km high glaciers don't form over night.

For reference for a a relatively small change in the amount of sunlight can have very large impact, Read up on: "Year without a summer".

This doesn't really address how life would adopt but there are bigger issues to determine first.

But over the longer haul for less severe dimming: Tundra and alpine biomes would spread, rain forests would diminish, deserts grow.

If it is 'very dim' to the point bioluminescence is useful during some part of the day. The world would be well on its way to complete snowball and mass extinctions with perhaps extinction of all life.

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    $\begingroup$ I think life is too tenacious for that. Things will go on feeding on other things until the system is completely devoid of energy. You're looking at a world dominanted by sapphrophytes (things - like fungi - that feed of dead things). I would imagine plants evolving to be more sapphrophytic. $\endgroup$ May 20 at 7:24
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Fungus is now king

Most plant life on earth survives via Photosynthesis.
Fungi however do not. They thrive in low-light conditions and dark, wet places.

Your twilight world is a place of spores and huge mushrooms.
Every surface is coated in fungal threads and slippery with slime-moulds

Any wildlife that wasn't able to switch to a mushroom diet has either died, or now feeds on the creatures that do.

Terrifyingly, variations on the famous Cordyceps fungus now infect many animals, driving them to unnatural behaviours and coating them in mushrooms themselves.

Many of your fungi and slimes are bioluminescent, particularly under blacklights. They might even be pretty. But ultimately the shadowy post-apocalyptic world your survivors enter is a horror-show for people who expect leaves and flowers. unsettling, dark, gloomy, wet and slimy.
The spores settle in your lungs, producing horrendous coughing fits and unpleasant messy deaths for anyone not wearing a respirator mask.
Most animals have evolved thick nostril-hair to protect themselves from this fate, though it doesn't always work.

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  • $\begingroup$ Oh wow, that's incredible!! It sparks so much questions and ideas! My challenge is now to think about how will the people go from this to the nice, pretty and modern civilization I have in mind ;) Thanks a lot! $\endgroup$
    – Lulullia
    May 19 at 16:13
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    $\begingroup$ The problem is that Fungi live off decaying organic matter and if everything else is dead that would not be replenished leading to the death of the fungi as well. So at least some other vegetation needs to survive. If the equator becomes like the arctic then coniferous trees might live there. $\endgroup$
    – Slarty
    May 19 at 18:34
  • $\begingroup$ @Slarty Note that it's not a completely pitch-black world. There is light. Just not a lot of it, so there'll be plant-life clinging on here and there. A lot of animals will have developed (rapidly) to have better low-light vision as well. $\endgroup$
    – Ruadhan
    May 20 at 8:28
  • $\begingroup$ That's a fair point - but it means the devil is in the detail of exactly how much light there is and what counts as "rapidly" $\endgroup$
    – Slarty
    May 20 at 11:37
  • $\begingroup$ @Slarty Nice thing about writing a story is that Anthropic Principle is in full effect at all times. It doesn't really matter how improbable something is. The story is set in a world where it managed to happen despite the odds. As long as it's possible, this is the world where it happened. A lot of wildlife does most of their activities at dusk anyway, so it's not so "out there" that they'd become accustomed to a world of twilight and darkness. $\endgroup$
    – Ruadhan
    May 20 at 14:56
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What your describe pretty much nuclear winter but far longer. Your world is covered an ice and snow. The oceans are frozen over.

Plants and animals would die in mass. You would have lower temperatures then the Artic. All together you have a frozen and mostly dead world. The only thing left alive would be fungi and ocean floor Dwellers and as for how they could evolve who could say.

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    $\begingroup$ But what if the world didn't freeze? well you know what I think I just skipped a big step, I have to focus first on how to keep a temperature similar to Earth even without sunlight. I'll make a new question and come back to this once I have more details on the environment. Thanks! $\endgroup$
    – Lulullia
    May 19 at 17:18
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    $\begingroup$ Preventing a snowball earth is going to be very, very hard, even if you only block one or two percent of the light hitting earth. Perhaps if you move all of the continents to the poles first, you can get away with a couple percent? Wouldn't bet on it. And recovering from a snowball earth now, with less insolation, will be even harder than last time it (might) have happened -- you're talking atmospheric CO2 percentages building up to way over 10% from the current 0.04%, which will take millions of years. $\endgroup$
    – addaon
    May 19 at 18:40

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