How low can you go-- altitude, that is

Bren McDonnall

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Assuming an open air valley/canyon/depression, how far below sea level would it be plausible to live more or less normally? It looks like the lowest open air land on earth is in the Dead Sea region at about 413 meters. Is this about rock bottom (you should pardon the pun) or could people feasibly live lower down given open land?

I know there are mines that beggar that depth. The deepest seems to be around 3500 meters, but lies at an altitude of around 1440 meters, giving it's floor an altitude of around 2050 meters below sea level. There are significant issues with pressure down there, but I haven't been able to really ascertain how many of them are due to the fact that there's 3500 meters of rock pressing down on it.

Would it be feasible, for instance, for people to live and thrive at around 600 meters or so below sea level?

Thanks.
 

Curlz

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Open air or mine? You mention both. Mines are enclosed and that's a different problem than just living in a low, open air valley or canyon. The low altitude on surface is not a problem, unless you go way too low and have rivers of molten rock flowing through ;) The air doesn't go rare the way it does with higher altitudes. I'm not sure what problem you are thinking of.
...*scratches head*...*pulls beard*...
 

Bren McDonnall

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Open air. I mentioned the mines because they're so much deeper, and one of the concerns I had was with air pressure.
 

cbenoi1

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The problem with open mines is the rain. There needs to be heavy pumps to extract the water that constantly seeps in. If we're talking about deep tunnels and bores, you will have humidity-related problems like mildew, molds, etc. Some spores are poisonous and can cause severe breathing problems.

No worry about air pressure vs human physiology: humans can sustain up to 4x atmospheres just by diving a hundred feet in water. In open air, the effect would be minimal on the human body (~one inch of mercury - about 0.03 atmosphere - per 1000 feet down).

-cb
 

King Neptune

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I agree with Cbenoi1. Pressure would not be a problem, even at the center of the hollow Earth. In addition to air pressure increasing with depth, there is a similar effect with temperature, with the increase being about three degrees F per thousand feet, so the eight thousand feet, or so, to the center of the Earth would mean in increase of about 24 degrees F, which might be a problem.
This article says 2C per thousand feet, but it provides more explanation.
https://en.wikipedia.org/wiki/Lapse_rate
 

neandermagnon

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There's also the problem of cave gas/breathable air (or lack thereof). That is way more of an issue than air pressure or temperature. People who go mining/caving very deep have various breathing apparatus. Also, the canary test, i.e. lower a canary or other small bird in the mine shaft and see it it comes up alive, was used in the past to test if air is breathable. When on an adventure/activity holiday in Wales which included caving, we were warned that going even 100m underground poses a significant risk of being gassed/suffocated. How much this varies geographically I have no idea but I wouldn't be surprised if it's very variable depending on the types of rock, soil and organisms living in them. Even if the air is breathable at the start, ventilation would be limited so a large human population would quickly use up oxygen and breathe out CO2 - it wouldn't take long for CO2 to reach toxic levels in an enclosed system.

If the population has a high level of technology they'd be able to build machines that purify the air and maintain a steady supply of oxygen and also keep on removing CO2 but you'd need a sustainable way of doing this that works underground without producing too much heat. The high temperatures under the ground would be an issue, plus there's no way for heat to escape. Keeping the area cool would be challenging as air con systems rely on dumping the heat outside the building, i.e. part of the machine/system is outside the building and its purpose is to dissipate the heat. You don't have that option down a mine. If there's water flowing nearby that might be a way of dumping heat and other waste, but underground water also poses a risk - see cbenoi's post above. Plus there's the issue of disposal of sewage.
 

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There is no problem living in an open-air atmosphere having an atmosphere of higher elevation. It's just like the fish at the bottom of the sea. Organisms can accommodate pressure, either liquid or gaseous. However, go too deep, and you'll have problems returning quickly to sea level due to the behavior of nitrogen in the blood.

Cbenoi1 is right about the water. It's always going down, even in solid rock (which isn't as solid as we think), In fact, it was water in the British coal mines that led to the invention of the steam engine to pump it out. Until the steam engine came along, it was too expensive to transport coal very far before it became unprofitable. That's what kicked off the industrial revolution, and the right to own ideas, but that's another story...

regards,

DrDoc
 
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blacbird

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Humans could certainly survive at much lower altitude than that of the Dead Sea, as long as their was open atmosphere with free oxygen. Divers unprotected by pressure suits can get to around 500 feet (150+m) in water, where the pressures are much greater than those anywhere on the surface of Earth. Somebody more mathematical than me would need to do the conversion of an oceanic -150m pressure to the equivalent of that in free atmosphere.

caw
 

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Air circulation in a deep mine would be an issue (you need a ventilation system), and they get too hot to survive without AC (the deepest mines on Earth, in South Africa, are nearly 4km down), but I don't think increased air pressure is an issue. The rocks the mine is carved into won't affect the air pressure. It's not like being at the bottom of the ocean, where every 10 meters of water depth increases pressure by one atmosphere.

The pressure the rocks themselves are under do make the risk of cave ins or collapses a real concern, however. This article about proposed mines that could be as deep as 5k says that the barometric pressure at this depth would be 66% greater (about 1 2/3 atmospheres) than at the surface level (so it's maybe the equivalent of going down 7m into the water), which doesn't seem like much of an issue, if the person has healthy sinuses and eustacean tubes, since this depth is not enough to cause nitrogen narcosis or decompression sickness in recreational divers (unless they shoot to the surface at the end of their dive instead of swimming up gradually). But since miners are down there for long periods and are exposed to toxins that could be more hazardous under increased pressure, it is a concern.

https://www.saimm.co.za/Journal/v105n06p387.pdf

I don't know that toxins would be an issue for someone in a 4-5 km deep valley or dry sea on the surface of a planet with Earthlike atmospheric pressures. I'd be more inclined to wonder why such a depression wouldn't fill with water, unless said planet is very dry. And then it wouldn't likely have a very breathable atmosphere by human standards (little water=little photosynthesis=little free O2).

Air circulation wouldn't be an issue for such a deep canyon, obviously, since it would be open. It would still be hotter than an equivalent locale at sea level overall (think of the ideal gas laws), just as it is cooler up in the mountains (as atmospheric pressure decreases). Of course, other factors besides air pressure affect local temperatures as well.
 
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blacbird

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Air circulation wouldn't be an issue for such a deep canyon, obviously, since it would be open.

I wouldn't bet entirely on this concept. "Open" construction trenches have suffocated workers (very quickly) owing to settling of CO2, which is about 30% heavier than normal N2/O2 air. So the relative movement v. stagnancy of the atmosphere could be an issue. If the atmosphere was very calm and became stratified, that could be a problem.

caw
 
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Kevin Nelson

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Humans could certainly survive at much lower altitude than that of the Dead Sea, as long as their was open atmosphere with free oxygen. Divers unprotected by pressure suits can get to around 500 feet (150+m) in water, where the pressures are much greater than those anywhere on the surface of Earth. Somebody more mathematical than me would need to do the conversion of an oceanic -150m pressure to the equivalent of that in free atmosphere.

One atmosphere is equivalent to the pressure of 32 feet of water. So the pressure at that depth is about 16 times ordinary atmospheric pressure.

But scuba divers who go that low have to be very careful about what sort of breathing gas they use. Both oxygen and nitrogen can have bad effects under those pressures, so they typically use gas mixtures that contain a lot of helium. If you're going to be breathing ordinary air, it really shouldn't go above about 3 times ordinary atmospheric pressure.

To get that level of pressure in an open-air trench, you'd need to go about 10 kilometers below sea level.
 

blacbird

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One atmosphere is equivalent to the pressure of 32 feet of water. So the pressure at that depth is about 16 times ordinary atmospheric pressure.

But scuba divers who go that low have to be very careful about what sort of breathing gas they use. Both oxygen and nitrogen can have bad effects under those pressures, so they typically use gas mixtures that contain a lot of helium. If you're going to be breathing ordinary air, it really shouldn't go above about 3 times ordinary atmospheric pressure.

To get that level of pressure in an open-air trench, you'd need to go about 10 kilometers below sea level.

Thanks. Very useful. I'm a geologist. I hit rocks with a hammer. A geologist's concept of math is 2+2 =~4.

caw
 

Roxxsmom

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Would radon be an issue?

Depends on whether there are any uranium-bearing rocks in the nearby soil. Granite is a big culprit, as I understand it.

I wouldn't bet entirely on this concept. "Open" construction trenches have suffocated workers (very quickly) owing to settling of CO2, which is about 30% heavier than normal N2/O2 air. So the relative movement v. stagnancy of the atmosphere could be an issue. If the atmosphere was very calm and became stratified, that could be a problem.

caw

From the OP's question, I was envisioning something more open than a narrow trench or canyon, though.
 

Bren McDonnall

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Thank you all very much. This is exactly the sort of information I'm needing.

I'm working on a sort of alternate worlds through the portal thing. Certain items float at varying, but matching heights on both worlds. For instance, one common building material floats at around 5k feet above (Terran) sea level on both worlds. I was considering whether the altitude corresponding to that on the other world (through the portal) needed necessarily to be the same, or if their 'sea level' might be different.

I recognize that 'sea level' is a fixture of the equilibrium between atmosphere and water, but there are other factors in play on this other world that could mitigate this somewhat.

Still playing with the ancient super science and fine-tuning things.

For the record, the primary area where this would affect the story (the location of the initially discovered portal) is the caldera of a long dead supervolcano just larger than the Yellowstone Caldera.

Once again, thanks.
 

cbenoi1

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Just to summarize: air recycling and water pumping are absolute necessities to make the place livable. You need to take out the seeping water, CO2, radon, humidity, and bring in fresh air. If you are using a deep bore as a resting place for some ancient machine that has just been discovered, then you need to think about how it was discovered. Abandoned mines filled with fresh water are the resting place of many diving amateurs. Mining shafts are dark, and their layouts not well documented. It's a death labyrinth for those who venture in them.

http://geology.com/articles/abandoned-mines.shtml

-cb
 

WeaselFire

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Technically, you can go as low in altitude as the water table. Below that it's called drowning. If you look at the Earth, you'll find very few areas where the water table is far lower than sea level and those areas, such as Death Valley and the Dead Sea area have unique geography to enable it, as well as being in extremely dry regions.

The ancient Black Sea level was far lower than it's current level, allowing for civilizations on it's shore that are now far below the water level. The area around the Bosphorous opened to the Mediterranean and the Black Sea rose to that level, drowning those civilizations out. One theory supporting the story of Noah's flood. Over eons, water levels have risen and fallen across the globe, with a few areas seeing catastrophic changes.

I'm not sure why you're really worried about all this though. It's an alternate universe with what appears to be a separate set of physics to Earth, so writing it logically and plausibly takes care of all your concerns, even if it doesn't match Earth.

Jeff
 

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Assuming an open air valley/canyon/depression, how far below sea level would it be plausible to live more or less normally? It looks like the lowest open air land on earth is in the Dead Sea region at about 413 meters. Is this about rock bottom (you should pardon the pun) or could people feasibly live lower down given open land?

I know there are mines that beggar that depth. The deepest seems to be around 3500 meters, but lies at an altitude of around 1440 meters, giving it's floor an altitude of around 2050 meters below sea level. There are significant issues with pressure down there, but I haven't been able to really ascertain how many of them are due to the fact that there's 3500 meters of rock pressing down on it.

Would it be feasible, for instance, for people to live and thrive at around 600 meters or so below sea level?

Thanks.

My husband is a minerals surveyor who started off as an apprentice to British Coal. He's been down into lots of coal mines. I just asked him, and he said the deepest mine he's been into was about 2,500 metres below sea level, and that he thinks the deepest mines are some of South Africa's diamond mines, which are significantly deeper than that. Yes, those mines have very high death-rates but that's because of poor health and safety care, not because the mines are so deep.

He says he notices no difference in how he feels underground, apart from the smell of being there.

The air pressure isn't affected by the "3500 meters of rock pressing down on it". Being underground is not the same as being under water, where you have the weight of all the water above you pressing on you. If, however, there's a rockfall when you're underground then yep, it does suddenly become a problem.

Remember when you're underground water seeps in, radon too, as has already been mentioned. And what people often don't realise is that the further underground you go, the warmer it gets. I think the temperature increases by one degree Celcius for every 100m you go down, but please check that.

If you had a large dip below sea level which wasn't enclosed as most coal mines are, it would have to be in some very odd geography and geology for that dip to remain empty of water and radon, and CO2 would collect. You'd need something to deal with that.

Technically, you can go as low in altitude as the water table. Below that it's called drowning.

That made me snort my tea through my nose. You naughty Weasel, you.