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This isn’t a question about sustainability, but rather archaeology. Let’s assume you built a large underground complex, perhaps a bunker or a communal fallout shelter, in a geologically stable region and then used the air filtration systems to vent all the atmosphere inside once it was clear everyone inside was going to die one way or another (you can fill in the blanks here unless the circumstances seem important to you). With the shelter now vacuum-sealed behind a 100-ton steel door, tens of meters of dirt and multiple airlocks, how far in the future could you reasonably expect future archaeologists (human, alien, robot or whatever) to discover your preserved remains? A hundred years? A thousand? Ten thousand?

The actual corpses of the inhabitants are of secondary concern here. Obviously none of your machines will still be working after centuries or millennia of disuse without a seriously durable and long-lasting power supply far beyond our current capabilities, but would your descendants/those who discovered you still be able to identify them as machines and take them apart to examine the components? What about things like furniture and other trappings of human habitation? How well-preserved would these artifacts be during the journey into deep time?

I’m hoping I can stretch the lifespan of this shelter as a tomb or historical site well past the ten thousand year mark, but two thousand years would be sufficient for my purposes. As a bonus question, could you actually keep such a facility powered across this wide of a gulf if you relied on wind, solar, or geothermal power instead of nuclear and had some kind of robot or automated system to keep the power grid working? Or could such an arrangement not support a facility this size for more than a few decades/centuries?

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  • $\begingroup$ Tutankhamun's tomb clearly qualifies as an underground shelter, and its contents was preserved for 3245 years; I'd like to think we have better tech today. Have you ever visited a museum of history? We have furniture and jewelry thousands of years old. Some ancient Egyptian (or, for that matter, Mycenean) jewelry looks like new and could be worn today. As for keeping machinery working for millennia, good luck with that; working machinery means spare parts and a way to dissipate waste heat, and most probably also some sort of water intake and outflow... $\endgroup$ – AlexP Sep 29 '18 at 17:32
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    $\begingroup$ High tech stuff actually has a shorter preservation lifespan. Egyptian tombs are so well preserved because they are made out of stone. By nature of being made from a geologically created material stone structures tend to last for geological periods of time. Modern structures made from artificial materials tend to last a few decades after maintenance stops before they start crumbling. $\endgroup$ – TCAT117 Sep 29 '18 at 18:07
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    $\begingroup$ Nature abhors a vacuum, but not an atmosphere composed of a noble gas at 1 atm pressure. If the seal is broken in a location there will be slow diffusion, but with equal pressure each side there is a better chance of the seal surviving. Better chance of preservation if the space is filled with argon after venting the previous atmosphere. $\endgroup$ – KerrAvon2055 Sep 30 '18 at 2:39
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Location, location, location.

Weathering is not the same everywhere. The ability of a structure to withstand time depends on what time brings to it. In the Taklimakan desert the lack of water, salt and seismic activity means wood and animal tissue has survived for thousands of years. In Hawaii where there is rain, salt, critters and periodic shaking / lava it is a struggle to get built things to last a couple of decades.

Considerations like yours are directly relevant to the construction of long term nuclear waste storage facilities. Water is the main agent of entropy on the surface and so regions with little water above or below are ideal. Seismic stability is desirable, because your structure could crack and then ground squirrels move in. Another issue is corrosion stability; I thought this was interesting - http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-waste/storage-and-disposal-of-radioactive-waste.aspx - these folks clad their nuclear waste in copper for its long term corrosion resistance.

Maybe your door should be copper? I am skeptical about the vacuum because nature abhors it - I think that if not maintained that will not last too long. Your room will fill with outgassed decomposition products of the bodies pretty quick (since they will boil in vacuum) and other gases will make their way in sooner or later.

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Steel And Concrete Don't Keep Well

The thing about steel is that no matter what you do it will eventually oxidize completely. In many ancient steel artifacts if you hold a magnet up to them nothing will happen. This is because iron-oxide has totally replaced the entirety of the artifact. Steel as a load bearing item within a shelter would eventually oxidize enough that it no longer provided structural support and it would buckle, then collapse. Likewise, concrete is porous and tends to absorb water over time. Freeze/thaw cycles make cracks form allowing more water in, and eventually it crumbles as well. In terms of archaeology.

In addition, a vacuum would not keep for more than maybe a few years, if that. As Willik stated, nature abhors a vacuum and keeping an atmosphere reduced to a vacuum is something that requires constant maintenance and effort to sustain. Eventually a seal somewhere would degrade enough to give way and the atmosphere would gradually equalize with the outside.

Keeping a Facilitiy operational requires Constant Maintenance

Anyone who has ever been in the military can recall endless hour upon boring hours simply cleaning, painting, and maintaining their surroundings. This is more than just busy work for the brass to keep the enlisted too busy to get into trouble. Large facilities require constant maintenance to remain useful and functioning. Once that maintenance stops it is usually only a matter of years until the site is useless for whatever purpose it was designed for. Nuclear missile silos that were only decommissioned a few decades ago look like this now:

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Keep in mind that these are some of the most robust and high tech structures of this era. For ideas of what bunkers look like after just a century here is a portion of the maginot line from WW1:

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Alternate method of preservation

So lets say this shelter was built high in the mountains close to a glacier. The nuclear war kicks off. A nearby blast broke one of the seals on the air filtration system and it cannot be repaired in time to prevent everyone inside from dying to fallout exposure. In a moment of delirium the last survivor throws open the main doors and collapses in the entrance and dies. In the next few months water fills the bunker and as nuclear winter kicks into full swing it freezes solid. Layer after layer of snow piles up on top of the bunker and eventually glaciation has buried the entire thing in snow and ice. The bunker lays that way, frozen in ice for a few thousand years. Obviously it is not in a perfect state of operational repair, that would not be possible. But it is still in a remarkable state of preservation. Eventually it is unearthed and becomes a major cultural site and archaeological study since no other place had such a high degree of preservation associated with it. Here is an image of a plane frozen in a glacier from WW2:

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It was so well preserved they are actually repairing it to full working condition after almost a century under the ice. Perhaps it would be possible under the right conditions to freeze your bunker solid and leave it in a state of well enough preservation that your future archaeologists could reconstruct or repair parts of the bunker to re-produce functionality. It would be a very long stretch honestly, just finding a bunker well enough preserved after a thousand years to walk around inside and maybe find some intact skeletons would itself be an incredible occurrence. I do not see any way a bunker could be preserved in an operational state across such time-spans, but that is not necessary to make a site an incredible archaeological site. Even just finding a single intact body frozen in the ice like Otzi the iceman would be an astounding find. Since I am tossing so many pictures at you, here is Otzi the Iceman, incredibly preserved in ice along with all his personal effects and tools scattered around him when he died after 5300 years. The body was so well preserved that initially the police thought he was a murder victim or lost hiker from only a few years prior until they started finding copper age tools.

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