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The skyworld I'm currently working on used to be an Earthlike planet until a supernatural disaster struck. Dense, translucent gas billowed from geysers on the surface until the ocean of fog covered all terrain below about 1 kilometer of elevation. This would have happened in the span of several years.

The gas is inert, non-toxic, and not an actual chemical, though the density is probably around 0.5 g/cm^3. The most anomalous property is that objects immersed in the gas experience a passage of time about 30 times faster than objects outside. Due to the density, I think Earth's atmosphere would get displaced upwards a bit(?)

The civilizations at the time of the disaster are at a medieval level of technology and the planet has a similar fraction of land above one kilometer as does Earth. Some polities will doubtlessly be able to evacuate and bring domesticated and wild animals with them. What I'm interested in is whether enough ecosystems will survive in the long-term to sustain these high altitude civilizations. Will alpine vegetation be enough to support ecosystems when most vegetation dies? Will animals with the mobility to reach high elevation and animals introduced be able to form a new ecosystem in the short time frame? And will humans be able to live off of it?

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  • $\begingroup$ A gas that's "not an actual chemical"? $\endgroup$ – RonJohn Aug 1 '18 at 1:54
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    $\begingroup$ @RonJohn It's magic. Something, the most basic thing, in a fantasy world always has to be handwaved even if its consequences can be derived from natural law. Here, the gas is actually some kind of magical essence. $\endgroup$ – user199429 Aug 1 '18 at 3:24
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    $\begingroup$ "It's magic" doesn't mesh well with #science-based and #reality-check. $\endgroup$ – RonJohn Aug 1 '18 at 3:35
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    $\begingroup$ @RonJohn: I mean, if he can give enough self-consistent information about the properties of the fog to extrapolate the cause and effect I don't really see an issue. The fog could be made of well-wishes and fairy spit, but if it behaves predictably within an otherwise natural environment then it comes down to a physics thought experiment. $\endgroup$ – Era Aug 1 '18 at 4:47
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    $\begingroup$ @RonJohn, how the OP sets up the question isn't relevant. Regardless of how I make the fog, what will the impact of that fog be on planetary ecology? That meshes quite well with science-based and reality-check. We're not supposed to be judging questions by their backstory unless the backstory is intrinsically involved with the answer. This one isn't. HOWEVER, asking us to explain how an entire ecology will be affected is off-topic as too broad. Add to that the several questions you've asked on a one-specific-question/one-best-answer site and the Q will get closed. (*continued*) $\endgroup$ – JBH Aug 1 '18 at 5:17
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Ecosystems depend upon inputs from outside. While mountain forests and alpine biomes will have light for photosynthesis to occur, think about what else they need...

Heat. Not just daily heat from the sun, but the climate set by prevailing wind cycles over the oceans. Global translucence will change the planet's albedo, reflecting more (or less) energy back into space. The changed heat balance alters the strength and cycles of those prevailing winds, meaning that the mountain forest might quickly heat up or cool off out of season.

Water. The changed heat balance and prevailing winds seem likely to alter the hydrologic cycle enormously.

Your mountain forests --if they survive at all-- will be severely stressed, producing less oxygen at just the time all those lowlanders move up and start chopping them down for firewood and shelter. Hope it keeps raining, or the survivors won't last long.

And don't forget the speedy explosion of anerobic life down in the lowlands, making life unpleasantly stinky everywhere.

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The most anomalous property is that objects immersed in the gas experience a passage of time about 30 times faster than objects outside.

Thus, anyone who could see down into the fog would see things moving really fast. Think "video at 900 fps".

Due to the density, I think Earth's atmosphere would get displaced upwards a bit(?)

More than "a bit". :)

Will alpine vegetation be enough

According to https://www.fs.usda.gov/treesearch/pubs/52156 the Alpine ecosystem starts around 3 km, not 1 km. And it's above the tree line. So, the specific answer to this question is "no".

Alpine ecosystems are typically defined as those areas occurring above treeline, while recognizing that alpine ecosystems at a local scale may be found below this boundary for reasons including geology, geomorphology, and microclimate. The lower limit of the alpine ecosystems, the climatic treeline, varies with latitude across California, ranging from about 3500 m (to) 2700 m on Mount Shasta.

What I'm interested in is whether enough ecosystems will survive in the long-term to sustain these high altitude civilizations.

1 km is only 3300 feet, and that's not very high. Lot's a lots of vegetation at that level, and the temperature doesn't get too cool.

The two big fat problems which immediately come to mind are:

  1. there's not many places above 1 km (for example, there are only four in all the British Isles), and
  2. oxygen. A worldwide fog is going to cover the oceans, too, and therefore the plankton, etc (source of most of the world's oxygen) will die, and thus everything else will, too.
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  • $\begingroup$ Thanks for the feedback. Here's my response to the big fat problems. For the fact that there aren't many places above 1km, that's true. Take a look at this: calculatedearth.com set sea level to 1000m. There's quite a bit of land, such as the Tibetan plateau and the foothills of the Rocky Mountains that might be arable. Also, on a earthlike planet, there might simply be more of these. As for oxygen, could there plausibly be a preexisting population of aerial plankton that basically fills the role of those in the oceans? $\endgroup$ – user199429 Aug 1 '18 at 6:39
  • $\begingroup$ Aerial "stuff" can only be aerial if it so tiny that it floats on wind currents. Plankton is too big. But hey, "magic": that fog could generate oxygen for you. $\endgroup$ – RonJohn Aug 1 '18 at 13:06
  • $\begingroup$ I don't think they're too big. If we're talking about phytoplankton, there are types in the 2 micrometers range, which is about the size of bacteria. There's lots of airborne bacteria and protists in the atmosphere, even some in the stratosphere that live there permanently. $\endgroup$ – user199429 Aug 1 '18 at 17:58

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