# Air-filled cavern in the mantle?



## NerdyCavegirl (Jan 17, 2016)

Is there any way to have air-filled caverns or tunnels in the mantle of an earthlike planet? Perhaps inside a giant geode like in The Core? I know it's a stretch and that movie takes a lot of liberties, but most likely impossible is better than for sure impossible. So if there were any chance in hell of an air-filled cavern in such a hot dense enviroment, how could it possibly work? How deep could the caverns extend? Could a tunnel from that deep lead to the surface, or at least a cave deep in the crust? I don't need a whole hellish city, just a tunnel wide enough to crawl through and a few caves big enough to fight disembodied reality-warping Paleolithic pyrokinetics. The air doesn't even have to be breathable, just as long as the cavern isn't filled with liquid or solid.


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## K.S. Crooks (Jan 17, 2016)

The surface of the earth isn't completely uniform. we have oceans, lakes, deserts, mountains, forests, glaciers, etc. there are coal or oil deposits in some places, nickel or iron in others and so on. Inside the earth is the same. Yes certain regions are mostly one or two types of stone and minerals but again not everywhere is the same. there are places with more volcanoes and even locations where the mantle rises above the crust. A air-filled bubble in the mantle could be made by a large amount of water or lava creating a space and then receding; A collapse of material could or shift in tectonic plates could create the space; It could be the lower chamber or tunnels of a now extinct volcano. I found this on a quick search: Magma in Earth's Mantle Forms Deeper Than Once Thought | NSF - National Science Foundation

Create the location for your story. If you want a plausible reason for its existence there are plenty of ways this can be done. Whether you include this reason in your story is another choice to make. Either way don't let what you think is possible in the real world derail your writing...it's fiction after all.


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## scribbler (Jan 19, 2016)

You may want to check out a book by Jeff Long called, The Descent.  It deals with this same concept and may serve to answer some of your questions.


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## skip.knox (Jan 19, 2016)

If the work is science fiction, then I understand the need for some sort of explanation that is at least pseudo-scientific. But if it's fantasy, then why bother to explain. Our world has holes in it. Done and done. Or, you could even take advantage of it and invent myths as to why the big caverns. The reader recognizes them as myths, so doesn't expect them to be real, and the characters in your story won't be expected to believe anything more than the myths.

Is it the huge caverns that are crucial to the story, or is it the explanation that is crucial?


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## NerdyCavegirl (Jan 19, 2016)

skip.knox said:


> If the work is science fiction, then I understand the need for some sort of explanation that is at least pseudo-scientific. But if it's fantasy, then why bother to explain. Our world has holes in it. Done and done.



Because as I told you on my chimp thread, I have a certain way I process information when writing, and I preferto adhere as closely as possible to real-world physics even when planning out even the most outlandish concepts. I don't like restricting myself to the norms of specific genres. While I may be writing the narrative as fantasy, that's simply just because the characters lack an understanding of the underlying processes around them. There's no need to completely make up how something works when at least some fraction of it can possibly be explained by real-world physics. It's easier to keep things consistent that way, and analyzing how strangely the universe actually works can open the door into some pretty unsettling story conflict.


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## skip.knox (Jan 20, 2016)

That's cool. If it works for you, then it works for you.


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## Epaminondas (Jan 20, 2016)

If my memory on geodes is correct they form when hot water gets trapped inside certain types of rock. The water dissolves minerals into ions trapped in the water making the cavity bigger. I suppose as long as the surrounding rock was the right type and more water is always trying to get in you could conceivably get a large cavity. 
As the water cools it cant keep all of the ions dissolved in the solution and they begin to crystallize out. Generally the slower the water cools the bigger the crystals form. If the water cools too quickly you only get tiny crystals. 

If I'm wrong someone feel free to correct but that's what I remember from geology.


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## arbiter117 (Jan 23, 2016)

K.S. Crooks said:


> Either way don't let what you think is possible in the real world derail your writing...it's fiction after all.



Reality never stopped "20,000 leagues under the sea" from becoming a classic!  (earth's diameter is like 3000 leagues)

So do it to it and have the bubble in the the mantle! If scientists haven't found pockets of air, they might yet find a few!

Sent from my Nexus 5 using Tapatalk


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## Drakevarg (Jan 23, 2016)

I don't think "20,000 Leagues" was ever a reference to depth. It was just basically saying "a frankly unreasonable quantity of undersea travel."


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## arbiter117 (Jan 23, 2016)

Yeah, but people still didn't brush off the book as being (insert worst possible comment about a book and its author here)

Sent from my Nexus 5 using Tapatalk


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## Drakevarg (Jan 23, 2016)

Right, but point is, pretty sure Jules Verne knew the diameter of Earth. But yeah, that is a pretty common confusion from what I can tell.

As for the original question... yeah, I don't thing some sort of geode-like structure in the mantle sounds _that_ implausible, even if it would certainly be uninhabitable between atmospheric conditions, heat, and the fact that it could likely be crushed at any moment by millions of tons of molten metal in every direction.


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## skip.knox (Jan 23, 2016)

arbiter117 said:


> Reality never stopped "20,000 leagues under the sea" from becoming a classic!  (earth's diameter is like 3000 leagues)



I've always understood that the 20k was a measure of distance, not depth.


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## Ireth (Jan 23, 2016)

skip.knox said:


> I've always understood that the 20k was a measure of distance, not depth.



Isn't that the same thing? Depth is distance pointing downward.


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## TheKillerBs (Jan 23, 2016)

Ireth said:


> Isn't that the same thing? Depth is distance pointing downward.



It refers to the total distance that they traveled underwater, not at the depth to which they descended, which was a lot less than 20k.


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## Drakevarg (Jan 23, 2016)

Ireth said:


> Isn't that the same thing? Depth is distance pointing downward.



It might if "20,000 Leagues" implied "20,000 Leagues in a straight line" as opposed to "20,000 Leagues on our submarine's odometer."


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## NerdyCavegirl (Jan 23, 2016)

Drakevarg said:


> As for the original question... yeah, I don't thing some sort of geode-like structure in the mantle sounds _that_ implausible, even if it would certainly be uninhabitable between atmospheric conditions, heat, and the fact that it could likely be crushed at any moment by millions of tons of molten metal in every direction.



Ah that's the kind of unsettling conflict I refer to! For me, "uninhabitable" translates to "how can I help my poor characters help themselves not die?" What could be more harrowing than descending deep underground into a sun within your own world, skin blistering and body slowly crumpling despite all your fantastical gear and skills, hoping you have the strength to make it to the surface alive, with the knowledge that the  inferno could cave in and overwhelm you at any second? Even if you make it out alive, you'd live out your days knowing with all certainty that hell is just beneath the thin crust of your world.


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## Drakevarg (Jan 23, 2016)

Well, getting back out would also be difficult too, I imagine. I have no idea if the mantle has "currents" in it, though I imagine it does. If so, then your little geode-bubble is basically a piece of driftwood in a sea of lava. Whatever tunnel you used to get here won't be around when you decide to leave.


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## NerdyCavegirl (Jan 24, 2016)

Drakevarg said:


> Well, getting back out would also be difficult too, I imagine. I have no idea if the mantle has "currents" in it, though I imagine it does. If so, then your little geode-bubble is basically a piece of driftwood in a sea of lava. Whatever tunnel you used to get here won't be around when you decide to leave.



Well the mantle does have the convection that moves the tectonic plates, but if I recall correctly, this is quite slow. Either way, I can't imagine any tunnels would be particularly stable, which is why half the party that journeys to the center of the earth (not really, only about halfway there) end up disintegrated in front of their friends. Not to mention one of the few survivors already has PTSD going in from falling in lava a few years back, and his woman that also survives and saves his ass is just plain claustrophobic as hell. That's what I mean by science being my foundation, not my roof.


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