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  #51  
Old 09-11-2019, 10:44 PM
iamthewalrus(:3= is offline
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Originally Posted by DinoR View Post
You seem to be thinking in terms of the asteroid or comet that formed the Chicxulub crater and arguably killed the dinosaurs. It's estimated to have been 11-81 km in diameter and made a 150+ km crater. There's a couple other big craters that get close to or overlap the very bottom part of that size range. The video up top is estimates of what happens if we get struck by a 500 km diameter body. It's a whole different kind of hurt .
Yeah, the problem here is that the question is not sufficiently well defined to answer clearly.

The OP asks about a meteor that "will turn the entire surface into fire for a time period."

I think that that definition covers both the dinosaur killing one and the one in the video. Clearly, the video example is not survivable by humans or anything other than pretty deep-dwelling ocean or (maybe) cave life. But the dinosaur killing comet arguably meets the OP's definition and is (maybe? with luck?) survivable by some humans. I mean, birds survived it, and they can't build nuclear reactor driven submarines, so we've got a fighting chance.
  #52  
Old 09-12-2019, 03:17 AM
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The advantage humans have is technology and accumulated knowledge. We're incredibly adaptable omnivores, which also helps. If the only way to survive is to eat algae and rats we'll do that. That doesn't guarantee survival, you can always come up with a hopeless scenario, but it does help.

In theory, you could set up a habit in something like a deep salt mine, then when it's safe to venture onto the surface again you can jump start farming by actively working at it, rather than just letting the ecosystem regenerate on its own. Of course, there are bajillion variables involved and like I said you can always run into a hopeless situation.
  #53  
Old 09-12-2019, 04:58 PM
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Originally Posted by kanicbird View Post
Biosphere 1 and 2 turned into a sour rat and cockroach infested hell and still needed oxygen pumped in so the people can survive.
Biosphere 1 is the Earth. It's not yet a sour rat and cockroach infested hell, though we're working on it.

Personally, I don't see what submarines, space stations, etc. have to do with the question. They're all immensely mass and volume-limited, or in the case of Biosphere 2 there was a goal of a sustainable system. None of that matters here.

Humans are pretty simple to keep alive. We need air, food, and water. We need roughly 1 kg air/day, and probably need about 1 kg of CO2 scrubbing chemicals per day as well. We also need about 1 kg of food/day and maybe 2 kg of water. Let's round up to 10 kg/day of consumables.

That's 365 tons of total consumables per person for a century of underground living. That's nothing! Most stuff is around 1 ton per cubic meter, so a cube just 7 meters on a side is enough to store everything. Sure, we'll need some space so that the liquid oxygen doesn't evaporate right away, but that's all doable.

It would be easy to clear out a mine with plenty of storage for hundreds or thousands of people. No advanced recycling stuff necessary.

You would want some power for lighting and other minor luxuries, which could be provided with a Pu238 radioisotope generator. It has a reasonably long half-life and minimal shielding requirements. You wouldn't need much; just a few kilowatts would be fine to provide lighting for hundreds of people. The Pu won't go bad but you could keep a bunch of spare parts around for the other components if necessary.

Heat should not be a problem for a small shelter. The London Underground is getting rather warm lately, having heat-saturated the surrounding rock, but it's been going for 1.5 centuries and has a huge incoming heat flux. So I don't think that would be a problem with a relatively small population.

The social problems seem more difficult. The Wool series by Hugh Howey addresses this in a horrific but interesting way. It's not really that believable in the details (it's sci-fi, after all), but I did come away convinced that you'd need a pretty nasty-sounding social fabric if you're to have a remotely stable society in that position.

I think it goes without saying that we should target a ratio of, say, ten females for every male.
  #54  
Old 09-12-2019, 06:13 PM
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Originally Posted by Ellis Dee View Post
Even after an impact as depicted in the video upthread? The entire earth is on fire; wouldn't that burn off the oxygen? (He asks, literally from a place of complete ignorance...)
Oxygen in the Earth's atmosphere amounts to around 539 trillion tons (metric). In addition, "… that will turn the entire surface into fire …" may be a little misleading. Bear in mind that combustible material on Earth occupies less than 22% of the surface (by excluding just the oceans and Antarctica, which must be thence reduced significantly for mountains, reg, dunes and other barren areas). Which is to say that the aforementioned "fire" would in large fraction be lavaesque turmoil that consumes much less oxygen than wood, plants, flesh and other biological stuff. The air would get very stinky, but it seems unlikely that it would become fully bereft of oxygen. At least, in the short term – oxygen is noted for its habit of reacting with many things over time.

Last edited by eschereal; 09-12-2019 at 06:14 PM.
  #55  
Old 09-13-2019, 12:06 PM
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I wonder if a submarine crew could survive even a much larger comet.

I'm assuming that even a world-burning event like the one in the video would not wipe out sea life. A majority of oxygen production is from the sea. There's certainly plenty to eat as long as the sun is not so blocked out that the plankton and seaweed dies out.

The sub can make its own water and oxygen, so even if it takes a while for atmospheric oxygen to rebound, they probably have some kind of scuba or other breathing apparatus, so you give the guys who go out to fish supplemental oxygen.
  #56  
Old 09-13-2019, 04:21 PM
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Originally Posted by MartinLane View Post
A nuclear sub can stay underwater for several months. The food and a few other (classified) supplies are the limiting factors.

I think the only viable power supply for living underground if the surface is too hot for humans is nuclear power. If an impact is going to affect the surface that much, then it think it is reasonable to believe that the air will be too contaminated with dust and ash for diesel generators to work.

Given enough advance warning, an underground refuge could be made, but there is still the problem of a heat sink for the nuclear reactor if a steam plant is used to generate electricity. I suppose a cooling tower could be used, but if it fills with ash or dust, then is stops working. Any suggestions?
Geothermal heat pump? Along a horizontally bored shaft? Not going to work if the refuge is too deep---see Western Deep Levels and their Brobdingnagian refrigeration needs---but when does ambient underground temperature rise above, say, 72 F?
  #57  
Old 09-13-2019, 04:39 PM
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Originally Posted by iamthewalrus(:3= View Post
I wonder if a submarine crew could survive even a much larger comet.
Depending on the value of larger, of course. I don't know what survives a Melancholia level event.

(Clearly just an excuse to post that link, which should go directly to 7:02 in the video.)
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