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I've read a few answers here about how Earth's atmosphere is impossible to ignite with an atomic bomb. Is there some atmospheric mixture which could be both life-sustaining and able to ignite into a "slow burn" by such a blast?

Ideally I'm trying to come up with an apocalypse scenario for a world, and am open to other ideas. I'd like to keep things as plausible as possible:

  1. The primary survivors are the crews of a massive nuclear submarine fleet in the oceans. The deeper, human-reachable oceans need to stick around and be inhabitable for hopefully a few tens of thousands of years.
  2. The surface is rendered uninhabitable.
  3. The apocalypse doesn't need to be instantaneous, but should happen within a decade or so.

The run-away nuclear firestorm was only a first idea. I also considered:

  1. Planet becomes tidally-locked, one side fries and the other freezes. Issues: ocean might not remain, twilight zone habitable, no way to make the planet tidally-locked fast enough.
  2. The atmosphere is catastrophically ripped away by some massive cosmic event. Issues: would this wipe out the oceans too?

Thank you!

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  • $\begingroup$ In en.wikipedia.org/wiki/Battlefield_Earth_(novel) the Psychlos 'air' reacts with radioactive materials, they end up destroying the homeworld by teleporting some uranium there. $\endgroup$ – Robin Apr 24 '17 at 7:18
  • $\begingroup$ @Robin Unfortunately, that isn't science, that's bad fantasy. In fact, extremely bad fantasy. Also, 'borrowing' from other fiction, even if the 'ideas' are stinkers, isn't a good idea. Not to say, highly unoriginal. $\endgroup$ – a4android Apr 24 '17 at 7:44
  • $\begingroup$ Yet it might be worth taking a look at it no? Even if it is for the sake of learning what to not do. $\endgroup$ – Robin Apr 24 '17 at 7:51
  • $\begingroup$ Given that you present two non-nuclear options, what's the core goal here? Just making the surface uninhabitable, but (at least the deeper parts of) the oceans remain liquid and life-containing? $\endgroup$ – cometaryorbit Apr 24 '17 at 10:25
  • $\begingroup$ @cometaryorbit Yes, you are correct. My goal is to make the surface permanently uninhabitable but let anyone in one of these subs survive in a liquid ocean. I don't mind if humanity has a bit of time and sees the disaster coming, so long as the disaster arrives on non-geologic timescales. $\endgroup$ – user9657 Apr 24 '17 at 16:34
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I was thinking just the other day about how our world contains loads of reduced carbon existing in equilibrium with oxygen ready to burn it. Sometimes it burns! Mostly not. It seems like a delicate balance.

When things get hot and dry the balance tips and that is when you see things like wildfires. I read that the asteroid that killed the dinosaurs did so by superheating the atmosphere (pieces of asteroid / crust thrown up above the atmosphere fell back down, heating on re-entry and heating the atmosphere to the point where everything burns).

In the atmosphere itself, oxidizible stuff tends to oxidize. Methane being an example. Not loads floating around.

But suppose a big load of hydrocarbons arrived from space. There are plenty of entities in the solar system made of that stuff. It enters, hits etc but in addition to typical asteroid chaos, all that hot hydrocarbon reacts with our oxygen. Each chunk of superheated hydrocarbon asteroid produces a runaway Dresdenlike firestorm with giant winds pulling in the air, where it combusts and shoots chimney like upwards. Before long the oxygen is gone.

I can imagine a scenario where Titan is pulverized by some gravitic mishap. On earth we can see a cloud of debris coming our way. Pieces are big but none are dinosaur killer size meterorites and so the thought it we will able to ride it out. The oxygen-eating ability of these chunks of hydrocarbon is not considered.

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  • $\begingroup$ On geological timescale, exposed iron, coal etc indeed burns. That's what postponed oxygen crysis for so long. $\endgroup$ – Mołot Apr 24 '17 at 15:08
  • $\begingroup$ This sounds a lot like the "Hard Rain" from Neal Stephenson's Seveneves. I actually considered something like that for this purpose. Would such a huge impact do something too catastrophic like liquify the whole crust which might ruin the oceans? $\endgroup$ – user9657 Apr 24 '17 at 16:41
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    $\begingroup$ /huge impact/ You could spread out the impact with a bunch of medium sized meteorites. That would also avoid the problem of one giant one consuming all local oxygen then going out. $\endgroup$ – Willk Apr 24 '17 at 20:41
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The concept of creating a nuclear firestorm is an old one. Unfortunately, it's also a thoroughly debunked one.

Your attention is directed to this excellent article "(The Impossibility of) Lighting Atmospheric Fire", prepared as coursework by Doowong Chung at Stanford University.

To put it bluntly Chung's article details how this fear of nuclear atmospheric ignition has not only kept on recurring, but how has been constantly been debunked.

Bethe's rebuttal simply refers to and provides an overview of the Los Alamos Laboratory report LA-602 by E. J. Konopinski, C. Marvin, and—oddly enough—Edward Teller (pictured in Fig. 2), the original proponent of the thermonuclear weapon. According to Bethe, although the report was circulated in 1946 and declassified in 1973, "[t]his work was done before the first nuclear test at Alamogordo in July 1945," and its exclusion of atmospheric ignition unaffected by the subsequent development of fusion weapons. [8] This report, titled "Ignition of the Atmosphere with Nuclear Bombs", gives a detailed accounting of possible energy gain and loss mechanisms that would contribute to—or rule out—a global fusion catastrophe.

This rebuttal was made in 1975 over concerns about thermonuclear weapons. It was not the first and, probably not the last. This was first raised in the 1940s during the Manhattan Project and immediately prior to the Trinity test. Amusingly it was even raised during the development of nuclear weapons by Nazi Germany.

In his memoirs, Albert Speer recounts Heisenberg's evasiveness as to the question of whether fission was guaranteed to be controlled:

Actually, Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction. Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star. Occasionally, however, he joked that the scientists in their unworldly urge to lay bare all the secrets under heaven might some day set the globe on fire.

The report LA-602 looked into the atmospheric ignition in detail. This was in the 1940s.

The report first establishes a few key facts: that detonation of a nuclear bomb "produces a high temperature which will stimulate the reaction of atomic nuclei of the air with each other" and that this will propagate to the entire atmosphere "[i]f an ignition point exists and is surpassed". [9] This, perhaps trivially, would require "that the energy production in each newly entered region exceed the losses from that region." [9]

For energy gains, the report chiefly considers runaway nitrogen-nitrogen reactions, with additional consideration given to reactions involving protons, as nitrogen nuclei were perhaps the least stable element present in the atmosphere in significant quantities. In particular, the reaction that Konopinski et al. saw as "adopting the most dangerous assumptions" was [9]

N14 + N14 → Mg24 + α + 17.7 MeV

The energy that results from this reaction is enough to surmount the Coulomb barriers of the product particles, which is given as approximately 7 MeV, which, as Bethe explains, means that "the product nuclei can emerge from the reaction without any difficulty." [8,9]

Due to lack of empirical knowledge of nitrogen-nitrogen cross sections, the report makes certain simplified assumptions about the reaction cross section, allowing for an expression for the energy production rate per nitrogen nucleus, dependent on the temperature. Konopinski et al. also consider the nitrogen-proton reaction given by

N14 + p → C11 + α + 3.0 MeV

and here too, the produced energy surmounts the Coulomb barriers of the product particles (given as approximately 2.3 MeV). However, due to the much lower reaction cross-section and energy yield compared to the N-N reaction, the report argues that the energy contribution of this reaction would not be significant.

Essentially the detonation of nuclear weapons is unlikely to ignite the atmosphere to create a nuclear firestorm. If it did, despite the fact this is highly improbable, the nuclear firestorm won't be a slow burn. It will be over very quickly. However, it would require an exceptionally powerful nuclear explosion to ignite the atmosphere. Sufficiently powerful to be considered highly improbable. Perhaps a hypertechnological alien civilization might be able to do it. But that starts getting silly.

This means a nuclear firestorm is off the menu for creating an apocalypse. You may have to consider other possibilities.

EDIT:

For clarification this answer is based on the concept that if a nuclear firestorm cannot be triggered in the atmosphere of planet Earth it cannot happen in the atmosphere of any other life-sustaining planet. Planets with atmospheres dominated by hydrogen such as gas giant planets may be more susceptible to nuclear firestorms, but that will be left as an exercise for the reader. Also, their atmospheres are not life supporting, at least, not in the sense that human life is, and the OP wants human being involved in the apocalypse.

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    $\begingroup$ It is true for our atmosphere, all right. But it seems OP asks us to create atmosphere that could both ignite and support some kind of life. No requirement it's our atmosphere, our kind of life, or even to occur naturally. Your answer does not prove such atmosphere cannot exist. Or if it does, please make it stand out more. $\endgroup$ – Mołot Apr 24 '17 at 8:52
  • $\begingroup$ @Mołot The OP appears to be asking for a variation of our atmosphere that is nuclear ignitable and still support life. The question refers to "human-reachable oceans". If this is meant to be another planet that's not clear in the question. I was taking our atmosphere as a type example on the basis that if it can't work here it won't work elsewhere. i will edit my answer accordingly. $\endgroup$ – a4android Apr 24 '17 at 10:46
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    $\begingroup$ @Mołot I should have included this in my comment above. But thanks for raising the points that you did as it helped me clarify the main idea behind my answer. $\endgroup$ – a4android Apr 24 '17 at 10:51
  • $\begingroup$ My pleasure. I only pointed it out so you could clarify. Hence this "Or if it does, please make it stand out" part. $\endgroup$ – Mołot Apr 24 '17 at 10:55
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    $\begingroup$ "Actually, Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction." You mean Heisenberg was... uncertain? $\endgroup$ – F1Krazy Apr 24 '17 at 13:01
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One non-nuclear possibility is making the atmosphere unbreathable by biological means.

This could be a specifically designed bio-weapon that got out of hand. Maybe something like a fungus that becomes a fatal lung infection when inhaled (like super-histoplasmosis), but can also grow on and consume plastic, rubber, and other artificial polymers (somewhat like oil-eating bacteria, only on much higher molecular-weight petrochemicals?), thus making sealed above-water environments a lot more difficult to maintain.

However, it can't survive in salt water due to osmoregulation issues (too much salt pulls the water out of its cells).

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