6mo ago

A time traveler's survival guide. The vertical green bars are the only times in Earth's history with enough oxygen to breathe (hypoxia) and low enough to avoid oxygen toxicity (hyperoxia).

https://en.wikipedia.org/wiki/Hyperoxia

This was a screenshot I took months ago while watching a Geology Hub upload on YT. It was a lightbulb moment for my understanding of mass extinction events, (the largest was 250ma). I've referenced this multiple times, so thought I might share. Perhaps you find it as interesting as I do.

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42 comments

You can absolutely breathe higher partial oxygen pressure unaided for a long time. Hyperoxia isn't all that lethal and definitely not quickly, if you're only visiting, there's no problem.
And if you want to live there, you should be much more worried about all the brand new diseases you don't have immunity to, or the bugs that are bigger than you.
The low oxygen is definitely a problem, especially if you need to run away from the stuff mentioned above.
- Also someone like a proper Sherpa sherpa from the Himalayas can function with oxygen that's comparable to 7% sea level oxygen.
  And there are towns with elevation so high the oxygen is equivalent to 15% sea level oxygen.
  So this chart has pretty narrow limits. Sure, the legend does specify "breathe forever unaided", but someone like a well accustomed sherpa who regularly climbs Mt Everest would have a much wider range than 20-25%
  
  There are 850k people living in La Paz, Bolivia with the equivalent of 13.2% sea level oxygen and they seem to be doing just fine.
  
  No, no. I’ve seen the chart. They’re definitely dead by now.
  
  kagis
  https://www.reddit.com/r/askscience/comments/thj9zj/could_a_human_survive_on_a_planet_with_a_thinner/
  So, the answer is yes. The term "partial pressure" is often heard in this topic: as long as at least 0.2 bar of pressure are produced by oxygen alone, then you can add as much (or as little) as you want of a diluent gas on top of it. Of course this diluent gas has to be inert enough to avoid interfering with respiration, e.g. helium or nitrogen.
  I don't think that that's authoritative as a lower limit -- the guy is just saying that what matters is the partial pressure of oxygen. Assuming that that is right...
  There is an upper limit on the partial pressure of oxygen. Above 1.6 bars oxygen toxicity becomes a problem.
  Yup an a scuba diver, 1.6 at rest is the most we use while decompressing. 1.4 is the recommendation while exercising and 1.2 if you're doing a long dive.
  The military, as I understand it can push up to 2.0, but they have people that are super fit & they test people for oxygen tolerance too.
  These aren't gonna be hard limits, though, just maximums on what you'd subject a person to intentionally.
  https://www.checkyourmath.com/convert/pressure/atmospheres_bars.php
  There are 1.01325 bars in an atmosphere.
  https://en.wikipedia.org/wiki/Death_zone
  The concentration of oxygen (O2) in air is 20.9% so the partial pressure of O2 (PO2) at sea level is about 21.2 kPa (6.3 inHg; 3.07 psi).
  Humans have survived for 2 years at 5,950 m (19,520 ft) [475 millibars (14.0 inHg; 6.89 psi) of atmospheric pressure], which appears to be near the limit of the permanently tolerable highest altitude.[13]
  So "normal" at sea level is 1 atmosphere, with 20.9% of that being oxygen.
  If WP is correct, we can get down to 46% of that partial pressure of oxygen at normal atmospheric mix at sea level (though we couldn't be climbing mountains then, would cut into our survivable altitude range). So we could get down to 9.614% atmospheric oxygen and be okay at sea level.
  https://en.wikipedia.org/wiki/Oxygen_toxicity
  Lambertsen concluded in 1987 that 0.5 bar (50 kPa) could be tolerated indefinitely.
  So that'd be 50.7% oxygen, or about 2.42 times the partial pressure of oxygen at sea level.
  Going off that range -- 9.614% to 50.7% oxygen at sea level -- we could handle all of the oxygen levels on the chart. But two important caveats:
  That's only at sea level. The "dead zone" altitude on mountains and such would drop when the oxygen level is lower than it is in the current atmosphere.
  We probably wouldn't perform as well as we do today towards the extremes. It might be survivable, but "survivable" can be a long way from "biologically optimal".
  
  We probably wouldn't perform as well as we do today towards the extremes. It might be survivable, but "survivable" can be a long way from "biologically optimal".
  I often wonder about this. Is the increase in CO2 making us dumber?
  I'm certain the micro plastics and forever chemicals are messing with us majorly. It's causing more than just higher cancer rates, but all these things are hard to tease out, especially since global we're all being exposed to so many new poisons over the same time periods. It's in the rain, the soil, the oceans, and everywhere else
  It all just makes me think - how much potential are we each losing to subtle effects of pollution?
  
  I'd think that the aerosolized lead from leaded gasoline did far worse than any plastic or change in CO₂. There's still lots of volatile pollutants, like CO and hexavalent-anything out there.
- or the bugs that are bigger than you.
  Yea this was my takeaway. I think I'll only travel to times after insect megafauna go extinct.
- you should be much more worried about all the brand new diseases you don't have immunity to
  The diseases of amphibians, who are likely similiar to something you inherited from your mother already?
  
  If my immunity works on diseases from the early Devonian period, I’m just gonna skip my next covid booster
- We are merely the space ships of the microbes. Being caught between their war of the worlds would likely be unpleasant. However, I have a feeling we would be the true harbinger of death in that world of far more simple food webs than our present reality.
  Our deaths would be miserable upon return, due to the evolutionary life of our passengers having many millions of years to plot our deaths when we return to find a completely different world and the little ones waiting to say hello.
  I do not believe the table is intended for individual timescales, like how I tried to make the title more relatable. It is intended on geological timescales of species survival.
  IIRC the person on YT also mentioned there were times when there was not enough oxygen to sustain fire, which is another fascinating thought and helps make sense of things like hydrocarbon deposits like oil and coal in some instances.

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