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Is it possible for humans to survive on the surface of the Earth, assuming the Sun was, for some reason, not emitting any light/heat/other radiation? Would whether the Sun was actually present affect this survival?

EDIT: By survival I mean live long enough to give birth to a further generation.

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  • $\begingroup$ survive is a quite broad concept... one can survive 1 second or 90 years... $\endgroup$
    – L.Dutch
    Mar 16 '18 at 5:31
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    $\begingroup$ On the surface, not a chance. There is a chance to survive underground in bunkers with hydroponics, geothermal energy, and mining the atmosphere after it has turned into ice for oxygen and other gases. The ecosystem outside of the deepest parts of the ocean around volcanic vents is DEAD. $\endgroup$
    – Dan Clarke
    Mar 16 '18 at 6:11
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    $\begingroup$ Not a full answer, but if you want inspiration on how humans could survive without a sun, Fritz Leiber's A Pail of Air is a good, short sci-fi read. $\endgroup$
    – Giter
    Mar 16 '18 at 12:51
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Short answer is NO.

A slightly longer one is that the Earth's entire ecosystem (with a couple of very specific exceptions which I'll get to) is solar powered.

Plants use photosynthesis to produce O2 and carbohydrates. Photosynthesis is an endothermic (energy storing) reaction that takes water and CO2 and produces Oxygen and carbohydrates. The important point here is that the reason that plants use sunlight to do this is that they need to harvest energy to power the reaction. That energy is effectively 'stored' in chemical form, which they then reverse to extract their own energy and produce enough by-products (O2 and carbohydrates in their own biomass) that we in turn can also use those chemical forms to power us as we convert them back to CO2 and water.

So without the sun as a source of energy, no plants and no us. We'd suffocate first, but plants wouldn't last that long either as eventually all the atmospheric O2 would be converted to CO2 (via carbohydrate -> water conversion also) and even the plants would eventually suffocate or starve.

That said, there are some specific ecosystems on Earth, very deep in the ocean, where there is a large amount of life surrounding Black Smokers, a form of hydrothermal vent. These ecosystems use the thermal energy from these vents to support their life cycle, proving that the sun is not essential to ALL life on Earth, but these vents are unlikely to be able to support even a small human population even if we were down there.

Of course, we haven't even got onto the topic of planetary surface temperatures without the sun; the surface of the Earth would effectively go into a deep freeze, meaning that humans would not be able to survive even if O2 and food was available.

What all this means is that the Earth's life requires energy to survive. All animal life is parasitic to some degree, insofar as it consumes vegetation to survive. Even vegetation is parasitic as far as the Earth is concerned, harnessing the heat of the sun and the mineral content of the Earth to survive. Without that sun, the entire system breaks down as there is no energy entering the ecosystem to harvest or exploit.

We live on a planet that orbits its star at just the right distance to make life possible, introducing enough energy to keep water in a liquid form and to support the processes that are essential to life. This will not always be the case as the sun slowly expands to be a red giant. That will be the exact opposite of the scenario described in this question, but it will be no less lethal to life on this planet. When you get right down to it, our existence is a lot more fragile (and more improbable) than one might think.

The sun is an essential part of that existence, which would be impossible without it.

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  • $\begingroup$ How might they survive, then? Can they at all? $\endgroup$
    – adrian
    Mar 16 '18 at 4:52
  • $\begingroup$ Probably not. The O2 may last for a while, but without plants converting the CO2, the atmosphere would slowly turn toxic. I don't have numbers on how quickly that may happen and how quickly humans would die out from that, but my guess is that they'd freeze to death within weeks, if not days. $\endgroup$
    – Tim B II
    Mar 16 '18 at 5:59
  • $\begingroup$ Have you noticed how quickly the temperature goes down when night falls? Now imagine sun never rises again. The Earth would cool down very quickly. The best case scenario is about two years before the O2 in the atmosphere liquifies, according to washingtoncitypaper.com/columns/straight-dope/article/20782861/… $\endgroup$
    – Rekesoft
    Mar 16 '18 at 8:20
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    $\begingroup$ It would take many centuries without plants for atmospheric oxygen levels to fall to the point of unbreathabiltity, except that the atmosphere would freeze out long before that happened. $\endgroup$
    – Mike Scott
    Jan 26 '21 at 10:38
  • $\begingroup$ @adrian there is no surviving. Every single component of our diet is related with plants in a way or another, and unless we were to put in millions of lamps underground there'd be no way for any kind of plant to survive for long. And even if that was possible, the earth will freeze to temperatures low as never seen in history. Ever seen how many things survive in the center of the poles? Crank that cold up to 500 and you might get an slightly closer idea of what it'd be like. Unless they have interstellar travel and go to another earth-like planet which has a sun, they're doomed. $\endgroup$ Jan 26 '21 at 12:08
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A small population might survive by going underground and using geothermal and nuclear power to survive and grow food via artificial sunlight.

That being said long term survival (beyond a few decades) would be unlikely due to exhaustion of supplies, lack of raw resources for repairs and reactor fuel.

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