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Old 07-06-2022, 02:52 AM   #1
Johnny1A.2
 
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Default How long would the air on a dead world stay breathable?

Here's a bit of a geeky question: assume an Earth-like world with an Earth-like overall biosphere and atmosphere, one that would be well-suited to human habitation 'as is'.

Now assume that Something (a nearby supernova, a curse, whatever) kills all the biological life, including the unicellular forms, in a short time (a few hours, days, or less than a year, anyway).

What I was wondering was how long after the Event that the air would remain breathable to later visiting humans, since the free oxygen is no longer being biologically replenished (and probably a lot of dead biomatter is gonna burn, there's still lightning, after all, to start fires, volcanoes, etc, and no microorganisms to break down dead biomatter, so it'll sit there until something destroys it). Plus of course there's ongoing inorganic reactions with minerals and so forth taking O2 out of the air as well.

If a ship comes by a century or two later, would the air still have enough O2 to be breathable?

(Recognizing that the answer is necessarily a guesstimate.)
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Old 07-06-2022, 03:54 AM   #2
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Default Re: How long would the air on a dead world stay breathable?

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Originally Posted by Johnny1A.2 View Post
Here's a bit of a geeky question: assume an Earth-like world with an Earth-like overall biosphere and atmosphere, one that would be well-suited to human habitation 'as is'.

Now assume that Something (a nearby supernova, a curse, whatever) kills all the biological life, including the unicellular forms, in a short time (a few hours, days, or less than a year, anyway).

What I was wondering was how long after the Event that the air would remain breathable to later visiting humans, since the free oxygen is no longer being biologically replenished (and probably a lot of dead biomatter is gonna burn, there's still lightning, after all, to start fires, volcanoes, etc, and no microorganisms to break down dead biomatter, so it'll sit there until something destroys it). Plus of course there's ongoing inorganic reactions with minerals and so forth taking O2 out of the air as well.

If a ship comes by a century or two later, would the air still have enough O2 to be breathable?

(Recognizing that the answer is necessarily a guesstimate.)
A starting point for this inquiry might be https://en.wikipedia.org/wiki/Future...olar_evolution . The estimate there is that when photosynthesis stops working and plant life becomes extinct, animal life will follow it in a few million years, with large mammals dying off first. But that suggests that it's a matter of geological time. If large mammals can persist for even 1% of that few million years, that's tens of millennia. Checking into the work this estimate is based on might take you further.
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Old 07-08-2022, 03:54 AM   #3
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Default Re: How long would the air on a dead world stay breathable?

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The estimate there is that when photosynthesis stops working and plant life becomes extinct, animal life will follow it in a few million years, with large mammals dying off first. But that suggests that it's a matter of geological time. If large mammals can persist for even 1% of that few million years, that's tens of millennia.
That scenario seems implausible. What are the animals going to eat?
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Old 07-08-2022, 04:07 AM   #4
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Default Re: How long would the air on a dead world stay breathable?

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That scenario seems implausible. What are the animals going to eat?
Well, that's a good question. I'm not sure what the invertebrates that are likely to persist for millions of years will be eating, either. Decaying plants? Each other?
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Old 07-08-2022, 04:16 AM   #5
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Default Re: How long would the air on a dead world stay breathable?

If you read it you'll see that C4 photosynthesis remains viable for most of that period, and that some phytoplankton can survive all the way to the end, only eventually succumbing to temperature.
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Old 07-08-2022, 04:09 PM   #6
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Default Re: How long would the air on a dead world stay breathable?

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Originally Posted by johndallman View Post
That scenario seems implausible. What are the animals going to eat?
The movie 'Pitch Black' attempts to address this question, but some people think a biosphere dependent on marooned interstellar travellers is implausible.

:D
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Old 07-10-2022, 02:39 PM   #7
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Default Re: How long would the air on a dead world stay breathable?

ISTR a science program that dealt with the effects of a nearby gamma Ray burst hitting earth. Now if you're talking about an event that wiped out ALL life on earth, even down to microbes miles under the earth or living at the bottom of the deepest ocean it might take a massive close range GRB to do it.

From what I recall of the show, the radiation level would change earth's atmosphere almost instantly.


It's believed a powerful one hit earth 450 million years ago, causing a mass extinction event.

https://astrobiology.nasa.gov/news/h...-ray-burst-be/

A far weaker one from a greater distance may have grazed earth in the 8th century.

https://www.bbc.com/news/science-env...0caused%20this.

HTH.

Last edited by agentdenton; 07-10-2022 at 02:44 PM.
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Old 07-10-2022, 03:06 PM   #8
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Default Re: How long would the air on a dead world stay breathable?

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Originally Posted by agentdenton View Post
ISTR a science program that dealt with the effects of a nearby gamma Ray burst hitting earth. Now if you're talking about an event that wiped out ALL life on earth, even down to microbes miles under the earth or living at the bottom of the deepest ocean it might take a massive close range GRB to do it.

From what I recall of the show, the radiation level would change earth's atmosphere almost instantly.


It's believed a powerful one hit earth 450 million years ago, causing a mass extinction event.

https://astrobiology.nasa.gov/news/h...-ray-burst-be/

A far weaker one from a greater distance may have grazed earth in the 8th century.

https://www.bbc.com/news/science-env...0caused%20this.

HTH.
When I was researching GURPS Future History, I got the impression that GRBs ordinarily wouldn't inflict radiation poisoning on most living organisms:

Little direct radiation reaches the surface, but the atmosphere is chemically altered, being flooded with nitrogen compounds for several years (roll daily vs. HT to avoid 1 point of toxic damage).

That doesn't seem as if it would have a lot of effect on deep oceanic life, especially anaerobic life.
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Old 07-08-2022, 06:45 AM   #9
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Default Re: How long would the air on a dead world stay breathable?

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Originally Posted by Johnny1A.2 View Post
If a ship comes by a century or two later, would the air still have enough O2 to be breathable?
Yes. I did the math on this for the thread on timeline Lucifer-3. Based on Earth:

Total atmospheric oxygen: 1.4x10^15 tons. Total carbon in biomass (living and dead): 2.0x10^12 tons. Even if all of the carbon in biomass were fully oxidized, it would result in a 0.3% drop in atmospheric oxygen. Rusting and other inorganic surface oxidation processes remove about 6x10^8 tons of oxygen per year: significant on a geological time scale (~23,000 years for a 1% drop), but not in the couple of centuries you're asking about.
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Old 07-08-2022, 03:33 PM   #10
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Default Re: How long would the air on a dead world stay breathable?

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Originally Posted by thrash View Post
Yes. I did the math on this for the thread on timeline Lucifer-3. Based on Earth:

Total atmospheric oxygen: 1.4x10^15 tons. Total carbon in biomass (living and dead): 2.0x10^12 tons. Even if all of the carbon in biomass were fully oxidized, it would result in a 0.3% drop in atmospheric oxygen. Rusting and other inorganic surface oxidation processes remove about 6x10^8 tons of oxygen per year: significant on a geological time scale (~23,000 years for a 1% drop), but not in the couple of centuries you're asking about.
Now That's the kind of useful info I need. Thank you!
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